text: Laidler was a Fellow of the Royal Society of Canada, who described him "as one of the twentieth-century pioneers in the remarkable progress made in chemical kinetics leading to the development of transition state theory which provides the modern kinetic theory. Laidler's work includes seminal contributions in several areas of the field: gas phase reactions; kinetic aspects of reactivity of electronically excited molecules and construction of potential energy surfaces for such processes; development of treatments for kinetics and mechanisms for surface reactions and solution reactions, introducing modern concepts of solvation through dielectric polarization effects in the treatment of ionic redox reactions and of reactions producing or consuming ions; gas phase free-radical reactions involving pyrolysis and other thermal decomposition processes; and … the kinetics of enzyme-catalyzed reactions."

text: Laidler was a Fellow of the

entity_name: Royal Society of Canada

text: Royal Society of Canada

text: , who described him "as one of the twentieth-century pioneers in the remarkable progress made in

entity_name: Chemical kinetics

text: chemical kinetics

text: leading to the development of

entity_name: Transition state theory

text: transition state theory

text: which provides the modern kinetic theory. Laidler's work includes seminal contributions in several areas of the field: gas phase reactions; kinetic aspects of

entity_name: Reactivity (chemistry)

text: reactivity

text: of electronically

entity_name: Excited state

text: excited

text: molecules and construction of

entity_name: Potential energy surface

text: potential energy surface

text: s for such processes; development of treatments for kinetics and

entity_name: Reaction mechanism

text: mechanisms

text: for

entity_name: Reactions on surfaces

text: surface reactions

text: and

entity_name: Solution

text: solution

text: reactions, introducing modern concepts of

entity_name: Solvation

text: solvation

text: through

entity_name: Dielectric

entity_section: Dielectric polarization

text: dielectric polarization

text: effects in the treatment of ionic

entity_name: Redox

text: redox

text: reactions and of reactions producing or consuming ions; gas phase

entity_name: Radical (chemistry)

text: free-radical

text: reactions involving

entity_name: Pyrolysis

text: pyrolysis

text: and other

entity_name: Thermal decomposition

text: thermal decomposition

text: processes; and … the kinetics of

entity_name: Enzyme catalysis

text: enzyme-catalyzed

text: reactions."

method: UNH-ecn

text: The caramelization reactions are also sensitive to the chemical environment. By controlling the level of acidity (pH), the reaction rate (or the temperature at which the reaction occurs readily) can be altered. The rate of caramelization is generally lowest at near-neutral acidity (pH around 7), and accelerated under both acidic (especially pH below 3) and basic (especially pH above 9) conditions.

text: The caramelization reactions are also sensitive to the chemical environment. By controlling the level of acidity (

entity_name: PH

text: pH

text: ), the reaction rate (or the temperature at which the reaction occurs readily) can be altered. The rate of caramelization is generally lowest at near-neutral acidity (pH around 7), and accelerated under both acidic (especially pH below 3) and basic (especially pH above 9) conditions.

text: In quantum information theory, a quantum catalyst is a special ancillary quantum state whose presence enables certain local transformations that would otherwise by impossible.

text: In

entity_name: Quantum information

text: quantum information theory

text: , a quantum catalyst is a special

entity_name: Ancilla bit

text: ancillary

text: quantum state whose presence enables certain local transformations that would otherwise by impossible.

text: When a powder reacts chemically with a liquid or gas at the surface of its particles, the specific surface is directly related to its rate of reaction.  The measurement is therefore important in the manufacture of many processed materials.  It is universally used in the cement industry as a gauge of product fineness which is directly related to such properties as speed of setting and rate of strength development.

text: When a powder reacts chemically with a liquid or gas at the surface of its particles, the specific surface is directly related to its rate of reaction.  The measurement is therefore important in the manufacture of many processed materials.  It is universally used in the

entity_name: Cement

text: cement

text: industry as a gauge of product fineness which is directly related to such properties as speed of setting and rate of strength development.

text: The study of how substituents affect the reactivity of a molecule or the rate of reactions is of significant interest to chemists. Substituents can exert an effect through both steric and electronic interactions, the latter of which include resonance and inductive effects. The polarizability of molecule can also be affected. Most substituent effects are analyzed through linear free energy relationships (LFERs). The most common of these is the Hammett Plot Analysis. This analysis compares the effect of various substituents on the ionization of benzoic acid with their impact on diverse chemical systems. The parameters of the Hammett plots are sigma (σ) and rho (ρ). The value of σ indicates the acidity of substituted benzoic acid relative to the unsubstituted form. A positive σ value indicates the compound is more acidic, while a negative value indicates that the substituted version is less acidic. The ρ value is a measure of the sensitivity of the reaction to the change in substituent, but only measures inductive effects. Therefore, two new scales were produced that evaluate the stabilization of localized charge through resonance. One is σ, which concerns substituents that stabilize positive charges via resonance, and the other is σ which is for groups that stabilize negative charges via resonance. Hammett analysis can be used to help elucidate the possible mechanisms of a reaction. For example, if it is predicted that the transition state structure has a build-up of negative charge relative to the ground state structure, then electron-donating groups would be expected to increase the rate of the reaction.

text: The study of how substituents affect the reactivity of a molecule or the rate of reactions is of significant interest to chemists. Substituents can exert an effect through both

entity_name: Steric effects

text: steric

text: and electronic interactions, the latter of which include

entity_name: Resonance

text: resonance

text: and

entity_name: Inductive effect

text: inductive effects

text: . The

entity_name: Polarizability

text: polarizability

text: of molecule can also be affected. Most substituent effects are analyzed through

entity_name: Free-energy relationship

text: linear free energy relationships

text: (LFERs). The most common of these is the

entity_name: Hammett equation

text: Hammett Plot Analysis

text: . This analysis compares the effect of various substituents on the ionization of

entity_name: Benzoic acid

text: benzoic acid

text: with their impact on diverse chemical systems. The parameters of the Hammett plots are sigma (σ) and rho (ρ). The value of σ indicates the acidity of substituted benzoic acid relative to the unsubstituted form. A positive σ value indicates the compound is more acidic, while a negative value indicates that the substituted version is less acidic. The ρ value is a measure of the sensitivity of the reaction to the change in substituent, but only measures inductive effects. Therefore, two new scales were produced that evaluate the stabilization of localized charge through resonance. One is σ, which concerns substituents that stabilize positive charges via resonance, and the other is σ which is for groups that stabilize negative charges via resonance.

text: Hammett analysis

text: can be used to help elucidate the possible mechanisms of a reaction. For example, if it is predicted that the

entity_name: Transition state

text: transition state

text: structure has a build-up of negative charge relative to the ground state structure, then

entity_name: Polar effect

text: electron-donating groups

text: would be expected to increase the rate of the reaction.

method: Bert-ConvKNRM

text: Because of the higher Coulomb barrier, the temperatures required for H + He fusion are much higher than those of conventional D-T fusion. Moreover, since both reactants need to be mixed together to fuse, reactions between nuclei of the same reactant will occur, and the D-D reaction (H + H) does produce a neutron. Reaction rates vary with temperature, but the D-He reaction rate is never greater than 3.56 times the D-D reaction rate (see graph). Therefore, fusion using D-3He fuel at the right temperature and a D-lean fuel mixture, can produce a much lower neutron flux than D-T fusion, but is not clean, negating some of its main attraction.

text: Because of the higher

entity_name: Coulomb barrier

text: Coulomb barrier

text: , the temperatures required for H + He fusion are much higher than those of conventional

text: D-T fusion

text: . Moreover, since both reactants need to be mixed together to fuse, reactions between nuclei of the same reactant will occur, and the D-D reaction (H + H) does produce a

entity_name: Neutron

text: neutron

text: . Reaction rates vary with temperature, but the D-He reaction rate is never greater than 3.56 times the D-D reaction rate (see graph). Therefore, fusion using D-3He fuel at the right temperature and a D-lean fuel mixture, can produce a much lower neutron flux than D-T fusion, but is not clean, negating some of its main attraction.

text: In a chemical reaction, reactants collide to form a transition state, the enthalpic maximum in a reaction coordinate diagram, which proceeds to the product.  Normally, reactants form products of lesser chemical energy.  The difference in energy between reactants and products, represented as

text: In a chemical reaction, reactants collide to form a

text: transition state

text: , the

entity_name: Enthalpy

text: enthalpic

text: maximum in a reaction coordinate diagram, which proceeds to the product.  Normally, reactants form products of lesser chemical energy.  The difference in energy between reactants and products, represented as

text: The kinetics (relative rates of the reaction steps and the rate equation for the overall reaction) are explained in terms of the energy needed for the conversion of the reactants to the proposed transition states (molecular states that corresponds to  maxima on the reaction coordinates, and to saddle points on the  potential energy surface for the reaction).

text: The kinetics (relative rates of the reaction steps and the

entity_name: Rate equation

text: rate equation

text: for the overall reaction) are explained in terms of the energy needed for the conversion of the reactants to the proposed transition states (molecular states that corresponds to  maxima on the

entity_name: Reaction coordinate

text: reaction coordinates

text: , and to

entity_name: Saddle point

text: saddle point

text: s on the

text: potential energy surface

text: for the reaction).

text: The solid-state reaction route is the most widely used method for the preparation of polycrystalline solids from a mixture of solid starting materials. Solids do not react together at room temperature over normal time scales and it is necessary to heat them to much higher temperatures, often to 1000 to 1500 °C in order for the reaction to occur at an appreciable rate. The factors on which the feasibility and rate of a solid state reaction depend include, reaction conditions, structural properties of the reactants, surface area of the solids, their reactivity and the thermodynamic free energy change associated with the reaction.

text: The solid-state reaction route is the most widely used method for the preparation of

entity_name: Crystallite

text: polycrystalline

entity_name: Solid

text: solid

text: s from a mixture of solid starting materials. Solids do not

entity_name: Chemical reaction

text: react

text: together at room temperature over normal time scales and it is necessary to heat them to much higher temperatures, often to 1000 to 1500 °C in order for the reaction to occur at an appreciable rate. The factors on which the feasibility and rate of a solid state reaction depend include, reaction conditions, structural properties of the reactants,

entity_name: Surface area

text: surface area

text: of the solids, their

text: reactivity

text: and the

entity_name: Thermodynamic free energy

text: thermodynamic free energy

text: change associated with the reaction.

text: Deoxyribozymes, also called DNAzymes or catalytic DNA are first discovered in 1994. They are mostly single stranded DNA sequences isolated from a large pool of random DNA sequences through a combinatorial approach called in vitro selection or systematic evolution of ligands by exponential enrichment (SELEX). DNAzymes catalyze variety of chemical reactions including RNA-DNA cleavage, RNA-DNA ligation, amino acids phosphorylation-dephosphorylation, carbon-carbon bond formation, and etc.  DNAzymes can enhance catalytic rate of chemical reactions up to 100,000,000,000-fold over the uncatalyzed reaction. The most extensively studied class of DNAzymes are RNA-cleaving types which have been used to detect different metal ions and designing therapeutic agents. Several metal-specific DNAzymes have been reported including the GR-5 DNAzyme (lead-specific), the CA1-3 DNAzymes (copper-specific), the 39E DNAzyme (uranyl-specific) and the NaA43 DNAzyme (sodium-specific). The NaA43 DNAzyme, which is reported to be more than 10,000-fold selective for sodium over other metal ions, was used to make a real-time sodium sensor in living cells.

entity_name: Deoxyribozyme

text: Deoxyribozyme

text: s, also called DNAzymes or catalytic DNA are first discovered in 1994. They are mostly single stranded DNA sequences isolated from a large pool of random DNA sequences through a combinatorial approach called

entity_name: In vitro

text: in vitro

text: selection or

entity_name: Systematic evolution of ligands by exponential enrichment

text: systematic evolution of ligands by exponential enrichment

text: (SELEX). DNAzymes catalyze variety of chemical reactions including RNA-DNA cleavage, RNA-DNA ligation, amino acids phosphorylation-dephosphorylation, carbon-carbon bond formation, and etc.  DNAzymes can enhance catalytic rate of chemical reactions up to 100,000,000,000-fold over the uncatalyzed reaction. The most extensively studied class of DNAzymes are RNA-cleaving types which have been used to detect different metal ions and designing therapeutic agents. Several metal-specific DNAzymes have been reported including the GR-5 DNAzyme (lead-specific), the CA1-3 DNAzymes (copper-specific), the 39E DNAzyme (uranyl-specific) and the NaA43 DNAzyme (sodium-specific). The NaA43 DNAzyme, which is reported to be more than 10,000-fold selective for sodium over other metal ions, was used to make a real-time sodium sensor in living cells.

text: The graph for these equations is a sigmoid curve, which is typical for autocatalytic reactions: these chemical reactions proceed slowly at the start (the induction period) because there is little catalyst present, the rate of reaction increases progressively as the reaction proceeds as the amount of catalyst increases and then it again slows down as the reactant concentration decreases. If the concentration of a reactant or product in an experiment follows a sigmoid curve, the reaction may be autocatalytic.

text: The graph for these equations is a

entity_name: Sigmoid function

text: sigmoid curve

text: , which is typical for autocatalytic reactions: these chemical reactions proceed slowly at the start (the

entity_name: Induction period

text: induction period

text: ) because there is little catalyst present, the rate of reaction increases progressively as the reaction proceeds as the amount of catalyst increases and then it again slows down as the reactant concentration decreases. If the concentration of a reactant or product in an experiment follows a sigmoid curve, the reaction may be autocatalytic.

text: When a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction is said to have occurred. A chemical reaction is therefore a concept related to the "reaction" of a substance when it comes in close contact with another, whether as a mixture or a solution; exposure to some form of energy, or both. It results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels—often laboratory glassware.

text: When a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction is said to have occurred. A chemical reaction is therefore a concept related to the "reaction" of a substance when it comes in close contact with another, whether as a mixture or a

text: solution

text: ; exposure to some form of energy, or both. It results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels—often

entity_name: Laboratory glassware

text: laboratory glassware

text: In an industrial hydrodesulfurization unit, such as in a refinery, the hydrodesulfurization reaction takes place in a fixed-bed reactor at elevated temperatures ranging from 300 to 400 °C and elevated pressures ranging from 30 to 130 atmospheres of absolute pressure, typically in the presence of a catalyst consisting of an alumina base impregnated with cobalt and molybdenum (usually called a CoMo catalyst).  Occasionally, a combination of nickel and molybdenum (called NiMo) is used, in addition to the CoMo catalyst, for specific difficult-to-treat feed stocks, such as those containing a high level of chemically bound nitrogen.

text: In an industrial hydrodesulfurization unit, such as in a refinery, the hydrodesulfurization reaction takes place in a fixed-bed

entity_name: Chemical reactor

text: reactor

text: at elevated

entity_name: Temperature

text: temperatures

text: ranging from 300 to 400 °C and elevated

entity_name: Pressure

text: pressures

text: ranging from 30 to 130

entity_name: Atmosphere (unit)

text: atmosphere

text: s of absolute pressure, typically in the presence of a

entity_name: Catalysis

text: catalyst

text: consisting of an

entity_name: Aluminium oxide

text: alumina

text: base impregnated with

entity_name: Cobalt

text: cobalt

text: and

entity_name: Molybdenum

text: molybdenum

text: (usually called a CoMo catalyst).  Occasionally, a combination of

entity_name: Nickel

text: nickel

text: and

text: molybdenum

text: (called NiMo) is used, in addition to the CoMo catalyst, for specific difficult-to-treat feed stocks, such as those containing a high level of chemically bound nitrogen.

text: Diffusion-controlled (or diffusion-limited) reactions are reactions that occur so quickly that the reaction rate is the rate of transport of the reactants through the reaction medium (usually a solution).  As quickly as the reactants encounter each other, they react.  The process of chemical reaction can be considered as involving the diffusion of reactants until they encounter each other in the right stoichiometry and form an activated complex which can form the product species. The observed rate of chemical reactions is, generally speaking, the rate of the slowest or "rate determining" step. In diffusion controlled reactions the formation of products from the activated complex is much faster than the diffusion of reactants and thus the rate is governed by collision frequency.

text: Diffusion-controlled (or diffusion-limited)

text: reactions

text: are reactions that occur so quickly that the reaction rate is the rate of transport of the reactants through the reaction medium (usually a solution).  As quickly as the reactants encounter each other, they react.  The process of chemical reaction can be considered as involving the diffusion of reactants until they encounter each other in the right stoichiometry and form an activated complex which can form the product species. The observed rate of chemical reactions is, generally speaking, the rate of the slowest or "rate determining" step. In diffusion controlled reactions the formation of products from the

entity_name: Activated complex

text: activated complex

text: is much faster than the diffusion of reactants and thus the rate is governed by

entity_name: Collision frequency

text: collision frequency

method: UvABottomUpChangeOrder

text: In this sequence the carbons are numbered clockwise from 1–6 starting with the 1 carbon at 12 o'clock, which is bonded to the chloride. Since the nitro group is an activator toward nucleophilic substitution, and a meta director, it allows the benzene carbon to which it is bonded to have a negative charge. In the Meisenheimer complex, the nonbonded electrons of the carbanion become bonded to the aromatic pi system which allows the ipso carbon to temporarily bond with the hydroxyl group (-OH).  In order to return to a lower energy state, either the hydroxyl group leaves, or the chloride leaves.  In solution both processes happen.  A small percentage of the intermediate loses the chloride to become the product (2,4-dinitrophenol), while the rest return to the reactant.  Since 2,4-dinitrophenol is in a lower energy state it will not return to form the reactant, so after some time has passed, the reaction reaches chemical equilibrium that favors the 2,4-dinitrophenol.

text: In this sequence the carbons are numbered clockwise from 1–6 starting with the 1 carbon at 12 o'clock, which is bonded to the chloride. Since the

entity_name: Nitro compound

text: nitro

text: group is an activator toward nucleophilic substitution, and a meta director, it allows the benzene carbon to which it is bonded to have a negative charge. In the

entity_name: Meisenheimer complex

text: Meisenheimer complex

text: , the nonbonded electrons of the

entity_name: Carbanion

text: carbanion

text: become bonded to the aromatic pi system which allows the

entity_name: Arene substitution pattern

text: ipso

text: carbon to temporarily bond with the

entity_name: Hydroxy group

text: hydroxyl

text: group (-OH).  In order to return to a lower energy state, either the hydroxyl group leaves, or the chloride leaves.  In solution both processes happen.  A small percentage of the intermediate loses the chloride to become the product (2,4-dinitrophenol), while the rest return to the reactant.  Since 2,4-dinitrophenol is in a lower energy state it will not return to form the reactant, so after some time has passed, the reaction reaches

entity_name: Chemical equilibrium

text: chemical equilibrium

text: that favors the 2,4-dinitrophenol.

text: A compound can be converted to a different chemical composition by interaction with a second chemical compound via a chemical reaction. In this process, bonds between atoms are broken in both of the interacting compounds, and then bonds are reformed so that new associations are made between atoms. Schematically, this reaction could be described asAB + CD --> AC + BD, where A, B, C, and D are each unique atoms; and AB, CD, AC, and BD are each unique compounds.

text: A compound can be converted to a different chemical composition by interaction with a second chemical compound via a

text: chemical reaction

text: . In this process, bonds between atoms are broken in both of the interacting compounds, and then bonds are reformed so that new associations are made between atoms. Schematically, this reaction could be described asAB + CD --> AC + BD, where A, B, C, and D are each unique atoms; and AB, CD, AC, and BD are each unique compounds.

text: The resulting solution is called hydrochloric acid and is a strong acid. The acid dissociation or ionization constant, K, is large, which means HCl dissociates or ionizes practically completely in water. Even in the absence of water, hydrogen chloride can still act as an acid. For example, hydrogen chloride can dissolve in certain other solvents such as methanol, protonate molecules or ions, and serve as an acid-catalyst for chemical reactions where anhydrous (water-free) conditions are desired.

text: The resulting solution is called

text: hydrochloric acid

text: and is a

text: strong acid

text: . The

text: acid dissociation

text: or ionization constant, K, is large, which means HCl dissociates or ionizes practically completely in water. Even in the absence of water, hydrogen chloride can still act as an acid. For example, hydrogen chloride can dissolve in certain other solvents such as

text: methanol

text: protonate

text: molecules or ions, and serve as an acid-

text: catalyst

text: for chemical reactions where anhydrous (water-free) conditions are desired.

text: Like carbon, lithium is also a good energy conductor.  It's also already in use in commercial lithium-ion batteries.  Lithium makes a good energy conductor because it allows ions to transfer faster than other elements and is also able to hold on to that energy longer.  Research has shown that coating a phosphate particle with a layer of LiFePO4(Lithium iron Phosphate) allows for an even faster rate of ion transferral.  Lithium iron phosphate was made by solid-state reaction using Li2CO3(lithium carbonate), FeC2O4(Iron(II) Oxalate), and NH4H2PO4(ammonium dihydrogen phosphate).  The compounds were then placed in acetone and ball-milled(grinding materials together in a special cylindrical device) before being heated at 350 °C for 10 hours and then being allowed to cool to room temperature  The mixture was then pelletized under 10,000 pounds of pressure before being heated again at 600 °C for 10 hours under argon.  Each nanoball created measured around 50 nm(nanometers) in diameter.  Under normal circumstances, electrochemical systems (eg, batteries) can only achieve high power rates with supercapacitors.  Supercapacitors achieve a high power rate by storing energy through surface adsorption reactions of charged species on an electrode.  However, this results in low energy density. Instead of just storing charge on the surface of a material, Lithium iron phosphate can achieve a high power rate and high energy density by storing charge in the bulk of itself (the interior of the carbon nanoballs).  This is possible because lithium iron phosphate has high lithium bulk mobility. Creating a fast ion-conducting surface phase through controlled off-stoichiometry (controlling the mole to mole ratio of the reactants and products in the molecular equation) enabled an ultrafast discharge rate.

text: Calcium is reactive and relatively soft for a metal.  Although harder than lead, it can be cut with a knife with difficulty. It is a silvery metallic element that can be extracted by electrolysis from a fused salt like calcium chloride. When exposed to the air, it rapidly forms a gray-white coating of calcium oxide and calcium nitride. In bulk form (typically as chips or "turnings"), the metal is somewhat difficult to ignite, more difficult even than magnesium chips; but, when lit, the metal burns in air with a brilliant high-intensity orange-red light. Calcium metal reacts with water, producing hydrogen gas at a moderate rate without generating much heat, making it useful for generating hydrogen. In powdered form, however, the reaction with water is extremely rapid, as the increased surface area of the powder accelerates the reaction. Part of the reason for the slowness of the calcium–water reaction is a partial passivation (chemically protective coating) of insoluble white calcium hydroxide; in acidic solutions, where this compound is more soluble, calcium reacts vigorously.

text: Calcium is reactive and relatively soft for a metal.  Although harder than

text: lead

text: , it can be cut with a knife with difficulty. It is a silvery metallic element that can be extracted by

text: electrolysis

text: from a fused

text: salt

text: like

text: calcium chloride

text: . When exposed to the air, it rapidly forms a gray-white coating of

text: calcium oxide

text: and

text: calcium nitride

text: . In bulk form (typically as chips or "turnings"), the metal is somewhat difficult to ignite, more difficult even than magnesium chips; but, when lit, the metal burns in air with a brilliant high-intensity orange-red light. Calcium metal reacts with

text: water

text: , producing hydrogen gas at a moderate rate without generating much heat, making it useful for generating hydrogen. In powdered form, however, the reaction with water is extremely rapid, as the increased surface area of the powder accelerates the reaction. Part of the reason for the slowness of the calcium–water reaction is a partial

text: passivation

text: (chemically protective coating) of insoluble white

text: calcium hydroxide

text: ; in acidic solutions, where this compound is more soluble, calcium reacts vigorously.

text: Units and fluid systems in the plant including all vessels, piping, tubing, valves, pumps, compressors, and other equipment must be rated or designed to be able to withstand the entire range of pressures, temperatures, and other conditions which they could possibly encounter, including any appropriate safety factors.  All such units and equipment should also be checked for materials compatibility to ensure they can withstand long-term exposure to the chemicals they will come in contact with.  Any closed system in a plant which has a means of pressurizing possibly beyond the rating of its equipment, such as heating, exothermic reactions, or certain pumps or compressors, should have an appropriately sized pressure relief valve included to prevent overpressurization for safety.  Frequently all of these parameters (temperatures, pressures, flow, etc.) are exhaustively analyzed in combination through a Hazop or fault tree analysis, to ensure that the plant has no known risk of serious hazard.

text: Units and fluid systems in the plant including all vessels, piping, tubing, valves, pumps, compressors, and other equipment must be rated or designed to be able to withstand the entire range of pressures, temperatures, and other conditions which they could possibly encounter, including any appropriate

text: safety factor

text: s.  All such units and equipment should also be checked for

text: materials compatibility

text: to ensure they can withstand long-term exposure to the chemicals they will come in contact with.  Any closed system in a plant which has a means of pressurizing possibly beyond the rating of its equipment, such as heating, exothermic reactions, or certain pumps or compressors, should have an appropriately sized pressure

text: relief valve

text: included to prevent overpressurization for safety.  Frequently all of these parameters (temperatures, pressures, flow, etc.) are exhaustively analyzed in combination through a

text: Hazop

text: or

text: fault tree analysis

text: , to ensure that the plant has no known risk of serious hazard.

text: Capsule-based systems have in common that healing agents are encapsulated into suitable microstructures that rupture upon crack formation and lead to a follow up process in order to restore the materials´properties. If the walls of the capsule are created too thick, they may not fracture when the crack approaches, but if they are too thin, they may rupture prematurely. In order for this process to happen at room temperature, and for the reactants to remain in a monomeric state within the capsule, a catalyst is also imbedded into the thermoset. The catalyst lowers the energy barrier of the reaction and allows the monomer to polymerize without the addition of heat. The capsules (often made of wax) around the monomer and the catalyst are important to maintain separation until the crack facilitates the reaction.In the capsule-catalyst system, the  encapsulated healing agent is released into the polymer matrix and reacts with the catalyst, already present in the matrix. There are many challenges in designing this type of material. First, the reactivity of the catalyst must be maintained even after it is enclosed in wax. Additionally, the monomer must flow at a sufficient rate (have low enough viscosity) to cover the entire crack before it is polymerized, or full healing capacity will not be reached. Finally, the catalyst must quickly dissolve into the monomer in order to react efficiently and prevent the crack from spreading further.

text: Capsule-based systems have in common that healing agents are encapsulated into suitable microstructures that rupture upon crack formation and lead to a follow up process in order to restore the materials´properties. If the walls of the capsule are created too thick, they may not fracture when the crack approaches, but if they are too thin, they may rupture prematurely. In order for this process to happen at room

text: temperature

text: , and for the reactants to remain in a monomeric state within the capsule, a

text: catalyst

text: is also imbedded into the thermoset. The catalyst lowers the

text: energy barrier

text: of the

text: reaction

text: and allows the monomer to polymerize without the addition of heat. The capsules (often made of

text: wax

text: ) around the monomer and the catalyst are important to maintain separation until the crack facilitates the reaction.In the capsule-catalyst system, the  encapsulated healing agent is released into the polymer matrix and reacts with the catalyst, already present in the matrix. There are many challenges in designing this type of material. First, the reactivity of the

text: catalyst

text: must be maintained even after it is enclosed in wax. Additionally, the monomer must flow at a sufficient rate (have low enough

text: viscosity

text: ) to cover the entire crack before it is polymerized, or full healing capacity will not be reached. Finally, the catalyst must quickly dissolve into the monomer in order to react efficiently and prevent the crack from spreading further.

text: In chemical kinetics, the order of reaction with respect to a given substance (such as reactant, catalyst or product) is defined as the index, or exponent, to which its concentration term in the rate equation is raised. For the typical rate equation of form

text: In

text: chemical kinetics

text: , the order of reaction with respect to a given substance (such as

text: reactant

text: catalyst

text: or

text: product

text: ) is defined as the

text: index

text: , or exponent, to which its

text: concentration

text: term in the

text: rate equation

text: is raised. For the typical rate equation of form

text: TST is used primarily  to understand qualitatively how chemical reactions take place. TST has been less successful in its original goal of calculating absolute reaction rate constants because the calculation of absolute reaction rates requires precise knowledge of potential energy surfaces, but it has been successful in calculating the standard enthalpy of activation (ΔH), the standard entropy of activation (ΔS), and the standard Gibbs energy of activation (ΔG) for a particular reaction if its rate constant has been experimentally determined.  (The  notation refers to the value of interest at the transition state.)

text: TST is used primarily  to understand qualitatively how chemical reactions take place. TST has been less successful in its original goal of calculating absolute reaction rate constants because the calculation of absolute reaction rates requires precise knowledge of potential energy surfaces, but it has been successful in calculating the standard

text: enthalpy

text: of activation (ΔH), the standard

text: entropy of activation

text: (ΔS), and the standard

text: Gibbs energy

text: of activation (ΔG) for a particular reaction if its rate constant has been experimentally determined.  (The  notation refers to the value of interest at the transition state.)

text: If a chemical reaction causes the release of heat, and the reaction itself happens faster at higher temperatures, then there is a high likelihood of positive feedback. If the heat produced is not removed from the reactants fast enough, thermal runaway can occur and very quickly lead to a chemical explosion.

text: If a chemical reaction causes

text: the release of heat

text: , and the reaction itself

text: happens faster

text: at higher temperatures, then there is a high likelihood of positive feedback. If the heat produced is not removed from the reactants fast enough,

text: thermal runaway

text: can occur and very quickly lead to a chemical

text: explosion

text: Hydrodealkylation is a chemical reaction that often involves reacting an aromatic hydrocarbon, such as toluene, in the presence of hydrogen gas to form a simpler aromatic hydrocarbon devoid of functional groups. An example is the conversion of 1,2,4-trimethylbenzene to xylene. This chemical process usually occurs at high temperature, at high pressure, or in the presence of a catalyst. These are predominantly transition metals, such as chromium or molybdenum.

text: Hydrodealkylation is a chemical reaction that often involves reacting an

text: aromatic hydrocarbon

text: , such as

text: toluene

text: , in the presence of

text: hydrogen

text: gas to form a simpler aromatic hydrocarbon devoid of

text: functional group

text: s. An example is the conversion of

text: to

text: xylene

text: . This chemical process usually occurs at high temperature, at high pressure, or in the presence of a

text: catalyst

text: . These are predominantly

text: transition metal

text: s, such as

text: chromium

text: or

text: molybdenum

text: A chemical reaction takes place only when the reacting particles collide. However, not all collisions are effective in causing the reaction. Products are formed only when the colliding particles possess a certain minimum energy called threshold energy. As a rule of thumb, reaction rates for many reactions double for every 10 degrees Celsius increase in temperature, For a given reaction, the ratio of its rate constant at a higher temperature to its rate constant at a lower temperature is known as its temperature coefficient (Q).  Q is commonly used as the ratio of rate constants that are 10 °C apart.

text: A chemical reaction takes place only when the reacting particles collide. However, not all collisions are effective in causing the reaction. Products are formed only when the colliding particles possess a certain minimum energy called threshold energy. As a

text: rule of thumb

text: , reaction rates for many reactions double for every 10 degrees

text: Celsius

text: increase in temperature, For a given reaction, the ratio of its rate constant at a higher temperature to its rate constant at a lower temperature is known as its temperature coefficient (Q).

text: Q

text: is commonly used as the ratio of rate constants that are 10 °C apart.

text: In a long partnership, Harcourt and William Esson studied the rates of chemical reactions.  Among the processes they investigated was the acid-catalyzed iodine clock reaction (iodide and hydrogen peroxide).  Their work showed that the reaction's changing rate was proportional to the concentration of reactants present. This result was later formalized by Guldberg and Waage as the law of mass action.  Harcourt and Esson also studied the reaction between oxalic acid and potassium permanganate.

text: In a long partnership, Harcourt and William Esson studied the rates of chemical reactions.  Among the processes they investigated was the acid-catalyzed

text: iodine clock reaction

text: (iodide and hydrogen peroxide).  Their work showed that the reaction's changing rate was proportional to the concentration of reactants present. This result was later formalized by Guldberg and Waage as the

text: law of mass action

text: .  Harcourt and Esson also studied the reaction between oxalic acid and potassium permanganate.

text: Reactions can increase or decrease their rates with pressure, depending on the value of ΔV. As an example of the possible magnitude of the pressure effect, some organic reactions were shown to double the reaction rate when the pressure was increased from atmospheric (0.1 MPa) to 50 MPa (which gives ΔV = −0.025 L/mol).

text: Heterogeneous catalysts are usually solids, powdered in order to maximize their surface area. Of particular importance in heterogeneous catalysis are the platinum group metals and other transition metals, which are used in hydrogenations, catalytic reforming and in the synthesis of commodity chemicals such as nitric acid and ammonia. Acids are an example of a homogeneous catalyst, they increase the nucleophilicity of carbonyls, allowing a reaction that would not otherwise proceed with electrophiles. The advantage of homogeneous catalysts is the ease of mixing them with the reactants, but they may also be difficult to separate from the products. Therefore, heterogeneous catalysts are preferred in many industrial processes.

text: Heterogeneous catalysts are usually solids, powdered in order to maximize their surface area. Of particular importance in heterogeneous catalysis are the

text: platinum group

text: metals and other transition metals, which are used in

text: hydrogenation

text: s,

text: catalytic reforming

text: and in the synthesis of commodity chemicals such as

text: nitric acid

text: and

text: ammonia

text: . Acids are an example of a homogeneous catalyst, they increase the nucleophilicity of

text: carbonyl

text: s, allowing a reaction that would not otherwise proceed with electrophiles. The advantage of homogeneous catalysts is the ease of mixing them with the reactants, but they may also be difficult to separate from the products. Therefore, heterogeneous catalysts are preferred in many industrial processes.

text: The Q temperature coefficient is a measure of the rate of change of a biological or chemical system as a consequence of increasing the temperature by 10 °C. There are many examples where the Q is used, one being the calculation of the nerve conduction velocity and another being calculating the contraction velocity of muscle fibres. It can also be applied to chemical reactions and many other systems.

text: The Q temperature coefficient is a measure of the rate of change of a biological or chemical system as a consequence of increasing the

text: temperature

text: by 10 °C. There are many examples where the Q is used, one being the calculation of the

text: nerve conduction velocity

text: and another being calculating the contraction velocity of

text: muscle fibre

text: s. It can also be applied to

text: chemical reaction

text: s and many other systems.

text: Kinetically, catalytic reactions are typical chemical reactions; i.e. the reaction rate depends on the frequency of contact of the reactants in the rate-determining step.  Usually, the catalyst participates in this slowest step, and rates are limited by amount of catalyst and its "activity".  In heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. A nanomaterial-based catalyst is an example of a heterogeneous catalyst. Analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts.

text: Kinetically

text: , catalytic reactions are typical

text: chemical reactions

text: ; i.e. the reaction rate depends on the frequency of contact of the reactants in the rate-determining step.  Usually, the catalyst participates in this slowest step, and rates are limited by amount of catalyst and its "activity".  In

text: heterogeneous catalysis

text: , the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. A

text: nanomaterial-based catalyst

text: is an example of a heterogeneous catalyst. Analogous events associated with

text: substrate

text: binding and product dissociation apply to homogeneous catalysts.

text: Enzymes  are macromolecular biological catalysts. Enzymes accelerate, or catalyze, chemical reactions. The molecules at the beginning of the process upon which enzymes may act are called substrates and the enzyme converts these into different molecules, called products. Almost all metabolic processes in the cell need enzymes in order to occur at rates fast enough to sustain life. The set of enzymes made in a cell determines which metabolic pathways occur in that cell. The study of enzymes is called enzymology.

text: Enzymes  are

text: macromolecular

text: biological

text: catalyst

text: s. Enzymes accelerate, or

text: catalyze

text: chemical reactions

text: . The molecules at the beginning of the process upon which enzymes may act are called

text: substrates

text: and the enzyme converts these into different molecules, called

text: products

text: . Almost all

text: metabolic processes

text: in the

text: cell

text: need enzymes in order to occur at rates fast enough to sustain life. The set of enzymes made in a cell determines which

text: metabolic pathway

text: s occur in that cell. The study of enzymes is called enzymology.

text: Like all catalysts, enzymes increase the rate of a reaction by lowering its activation energy. Some enzymes can make their conversion of substrate to product occur many millions of times faster. An extreme example is orotidine 5'-phosphate decarboxylase, which allows a reaction that would otherwise take millions of years to occur in milliseconds. Chemically, enzymes are like any catalyst and are not consumed in chemical reactions, nor do they alter the equilibrium of a reaction. Enzymes differ from most other catalysts by being much more specific. Enzyme activity can be affected by other molecules: inhibitors are molecules that decrease enzyme activity, and activators are molecules that increase activity. Many drugs and poisons are enzyme inhibitors. An enzyme's activity decreases markedly outside its optimal temperature and pH.

text: Like all catalysts, enzymes increase the

text: rate of a reaction

text: by lowering its

text: activation energy

text: . Some enzymes can make their conversion of substrate to product occur many millions of times faster. An extreme example is

text: orotidine 5'-phosphate decarboxylase

text: , which allows a reaction that would otherwise take millions of years to occur in milliseconds. Chemically, enzymes are like any catalyst and are not consumed in chemical reactions, nor do they alter the

text: equilibrium

text: of a reaction. Enzymes differ from most other catalysts by being much more specific. Enzyme activity can be affected by other molecules:

text: inhibitors

text: are molecules that decrease enzyme activity, and

text: activators

text: are molecules that increase activity. Many

text: drug

text: s and

text: poison

text: s are enzyme inhibitors. An enzyme's activity decreases markedly outside its optimal

text: temperature

text: and

text: pH

text: Finally, aconitase is thought to be associated with diabetes. Although the exact connection is still being determined, multiple theories exist. In a study of organs from mice with alloxan diabetes (experimentally induced diabetes) and genetic diabetes, lower aconitase activity was found to decrease the rates of metabolic reactions involving citrate, pyruvate, and malate. In addition, citrate concentration was observed to be unusually high. Since these abnormal data were found in diabetic mice, the study concluded that low aconitase activity is likely correlated with genetic and alloxan diabetes. Another theory is that, in diabetic hearts, accelerated phosphorylation of heart aconitase by protein kinase C causes aconitase to speed up the final step of its reverse reaction relative to its forward reaction.  That is, it converts isocitrate back to cis-aconitate more rapidly than usual, but the forward reaction proceeds at the usual rate. This imbalance may contribute to disrupted metabolism in diabetics.

text: Finally, aconitase is thought to be associated with

text: diabetes

text: . Although the exact connection is still being determined, multiple theories exist. In a study of organs from mice with alloxan diabetes (experimentally induced diabetes) and genetic diabetes, lower aconitase activity was found to decrease the rates of metabolic reactions involving citrate, pyruvate, and malate. In addition, citrate concentration was observed to be unusually high. Since these abnormal data were found in diabetic mice, the study concluded that low aconitase activity is likely correlated with genetic and alloxan diabetes. Another theory is that, in diabetic hearts, accelerated phosphorylation of heart aconitase by protein kinase C causes aconitase to speed up the final step of its reverse reaction relative to its forward reaction.  That is, it converts isocitrate back to cis-aconitate more rapidly than usual, but the forward reaction proceeds at the usual rate. This imbalance may contribute to disrupted metabolism in diabetics.

text: In 1989 it was demonstrated how light-sensitive chemical reactions could perform image processing. This led to an upsurge in the field of chemical computing.Andrew Adamatzky at the University of the West of England has demonstrated simple logic gates using reaction-diffusion processes. Furthermore, he has theoretically shown how a hypothetical "2 medium" modelled as a cellular automaton can perform computation.  Adamatzky was inspired by a theoretical article on computation by using balls on a billiard table to transfer this principle to the BZ-chemicals and replace the billiard balls with waves: if two waves meet in the solution, they create a third wave which is registered as a 1. He has tested the theory in practice and is working to produce some thousand chemical versions of logic gates to create a chemical pocket calculator.One of the problems with the present version of this technology is the speed of the waves; they only spread at a rate of a few millimeters per minute. According to Adamatzky, this problem can be eliminated by placing the gates very close to each other, to make sure the signals are transferred quickly. Another possibility could be new chemical reactions where waves propagate much faster.

text: In 1989 it was demonstrated how light-sensitive chemical reactions could perform

text: image processing

text: . This led to an upsurge in the field of chemical computing.

text: Andrew Adamatzky

text: at the

text: University of the West of England

text: has demonstrated simple logic gates using

text: reaction-diffusion

text: processes. Furthermore, he has theoretically shown how a hypothetical "2 medium" modelled as a

text: cellular automaton

text: can perform computation.  Adamatzky was inspired by a theoretical article on

text: computation by using balls on a billiard table

text: to transfer this principle to the BZ-chemicals and replace the billiard balls with waves: if two waves meet in the solution, they create a third wave which is registered as a 1. He has tested the theory in practice and is working to produce some thousand chemical versions of logic gates to create a chemical pocket calculator.One of the problems with the present version of this technology is the speed of the waves; they only spread at a rate of a few millimeters per minute. According to

text: Adamatzky

text: , this problem can be eliminated by placing the gates very close to each other, to make sure the signals are transferred quickly. Another possibility could be new chemical reactions where waves propagate much faster.

text: The electron transport chain consists of a spatially separated series of redox reactions in which electrons are transferred from a donor molecule to an acceptor molecule. The underlying force driving these reactions is the Gibbs free energy of the reactants and products. The Gibbs free energy is the energy available ("free") to do work.  Any reaction that decreases the overall Gibbs free energy of a system is thermodynamically spontaneous.

text: The electron transport chain consists of a spatially separated series of

text: redox reaction

text: s in which electrons are transferred from a donor molecule to an acceptor molecule. The underlying force driving these reactions is the

text: Gibbs free energy

text: of the reactants and products. The Gibbs free energy is the energy available ("free") to do work.  Any reaction that decreases the overall Gibbs free energy of a system is thermodynamically spontaneous.

text: These calculations are based on the assumption that all chemical reactions are in equilibrium. When a current flows in the circuit, equilibrium conditions are not achieved and the cell potential will usually be reduced by various mechanisms, such as the development of overpotentials. Also, since chemical reactions occur when the cell is producing power, the electrolyte concentrations change and the cell voltage is reduced. A consequence of the temperature dependency of standard potentials is that the voltage produced by a galvanic cell is also temperature dependent.

text: These calculations are based on the assumption that all chemical reactions are in equilibrium. When a current flows in the circuit, equilibrium conditions are not achieved and the cell potential will usually be reduced by various mechanisms, such as the development of

text: overpotential

text: s. Also, since chemical reactions occur when the cell is producing power, the electrolyte concentrations change and the cell voltage is reduced. A consequence of the temperature dependency of standard potentials is that the voltage produced by a galvanic cell is also temperature dependent.

text: Those generated from primary amines are unstable to the extent that they have never been isolated and very rarely been observed directly. In a 2007 study a hemiaminal substructure trapped in the cavity of a host-guest complex was studied with a chemical half-life of 30 minutes. Because both amine and carbonyl group are isolated in a cavity, hemiaminal formation is favored due to a high forward reaction rate comparable to an intramolecular reaction and also due to restricted access of external base (another amine) to the same cavity which would favor elimination of water to the imine.

text: Those generated from primary amines are unstable to the extent that they have never been isolated and very rarely been observed directly. In a 2007 study a hemiaminal substructure trapped in the cavity of a

text: host-guest complex

text: was studied with a

text: chemical half-life

text: of 30 minutes. Because both amine and carbonyl group are isolated in a cavity, hemiaminal formation is favored due to a high forward

text: reaction rate

text: comparable to an

text: intramolecular

text: reaction and also due to restricted access of external base (another amine) to the same cavity which would favor

text: elimination

text: of water to the imine.

text: Acid staining is not a dyeing or pigment-base coloring systems, but a chemical reaction. A mixture of water, mineral salts and a slight amount of muriatic acid is applied to the concrete surface. This chemical reaction with the existing minerals (primarily lime) in the concrete over a period of one to four hours creates new earth tone colors on the concrete surface. The concrete surface is later scrubbed to remove excess stain and neutralized by a basic solution of ammonia and water or baking soda (less likely to cause whiting later) to help raise the ph level back to normal level. Due to inconsistencies in the surface level of concrete floor, acid staining creates a variegated or mottled appearance that is unique to each slab. The color penetration ranges from 1/16 to 1/32 of an inch. Older exterior concrete surfaces may not color as well as interior surfaces because the environment has leached or percolated out the mineral content.  As well, any exposed aggregate (rocks) in worn concrete will not accept staining.

text: Acid

text: staining is not a dyeing or pigment-base coloring systems, but a

text: chemical reaction

text: . A mixture of

text: water

text: mineral salt

text: s and a slight amount of muriatic acid is applied to the concrete surface. This chemical reaction with the existing

text: mineral

text: s (primarily lime) in the concrete over a period of one to four hours creates new earth tone colors on the concrete surface. The concrete surface is later scrubbed to remove excess stain and neutralized by a basic solution of

text: ammonia

text: and water or baking soda (less likely to cause whiting later) to help raise the ph level back to normal level. Due to inconsistencies in the surface level of concrete floor, acid staining creates a variegated or mottled appearance that is unique to each slab. The color penetration ranges from 1/16 to 1/32 of an inch. Older exterior concrete surfaces may not color as well as interior surfaces because the environment has

text: leached

text: or

text: percolated

text: out the mineral content.  As well, any exposed aggregate (rocks) in worn concrete will not accept staining.

text: Epoxy resins typically require a precise mix of two components which form a third chemical. Depending on the properties required, the ratio may be anything from 1:1 or over 10:1, but in every case they must be mixed exactly. The final product is then a precise thermo-setting plastic. Until they are mixed the two elements are relatively inert, although the 'hardeners' tend to be more chemically active and should be protected from the atmosphere and moisture. The rate of the reaction can be changed by using different hardeners, which may change the nature of the final product, or by controlling the temperature.

text: Chemical oxidative polymerization is a traditional and commonly used method for the polymerization of aniline in large quantities. When aniline is mixed with an oxidant in an acidic solution, polymerization will occur. The most important parameter to be controlled in this method for the synthesis of polyaniline nanofibers is the domination of homogeneous nucleation over heterogeneous nucleation. Homogeneous nucleation describes when the nuclei are formed spontaneously in solution while heterogeneous nucleation describes when the nuclei are grown on other species. In the early stages of this polymerization, only nanofibers are formed since there are no heteronuclei available for heterogeneous nucleation. However, if the reaction is left uncontrolled, heterogeneous nucleation will begin to dominate as the polyaniline will preferentially grow on existing particles, leading to irreversible agglomeration. The reaction can be made to favor homogeneous nucleation throughout by increasing reaction speed, temperature of the reaction, and allowing the reaction to proceed without stirring.

text: Chemical oxidative polymerization is a traditional and commonly used method for the polymerization of aniline in large quantities. When aniline is mixed with an oxidant in an acidic solution, polymerization will occur. The most important parameter to be controlled in this method for the synthesis of polyaniline nanofibers is the domination of

text: homogeneous

text: nucleation over heterogeneous

text: nucleation

text: . Homogeneous nucleation describes when the nuclei are formed spontaneously in solution while heterogeneous nucleation describes when the nuclei are grown on other species. In the early stages of this polymerization, only nanofibers are formed since there are no heteronuclei available for heterogeneous nucleation. However, if the reaction is left uncontrolled, heterogeneous nucleation will begin to dominate as the polyaniline will preferentially grow on existing particles, leading to irreversible agglomeration. The reaction can be made to favor homogeneous nucleation throughout by increasing reaction speed, temperature of the reaction, and allowing the reaction to proceed without stirring.

text: Thomas would spend the rest of his career with Monsanto, becoming a member of its board of directors in 1942, vice president in 1943, executive vice president in 1947, president in 1950, and ultimately chairman of the board from 1960 to 1965. He subsequently  served as chairman of Monsanto's Finance Committee frm 1965 to 1968. He retired in 1970. In this time, Monsanto's annual sales grew from $34 million to $1.9 billion, and its expenditure on research from $6.2 million to 101.4 million. He researched the chemistry of hydrocarbons and polymers. In studying the chemical reactions between alkenes and dienes, particularly in the presence of an aluminium chloride catalyst, he developed the proton theory of aluminium chloride, which helped explain a variety of chemical reactions, including cracking, polymerization and dehydrogenation. This research culminated in the publication of his book Anhydrous Aluminum Chloride in Organic Chemistry in 1941.

text: Thomas would spend the rest of his career with Monsanto, becoming a member of its board of directors in 1942, vice president in 1943, executive vice president in 1947, president in 1950, and ultimately chairman of the board from 1960 to 1965. He subsequently  served as chairman of Monsanto's Finance Committee frm 1965 to 1968. He retired in 1970. In this time, Monsanto's annual sales grew from $34 million to $1.9 billion, and its expenditure on research from $6.2 million to 101.4 million. He researched the chemistry of

text: hydrocarbon

text: s and

text: polymer

text: s. In studying the chemical reactions between

text: alkene

text: s and

text: diene

text: s, particularly in the presence of an

text: aluminium chloride

text: catalyst

text: , he developed the proton theory of aluminium chloride, which helped explain a variety of chemical reactions, including

text: cracking

text: polymerization

text: and

text: dehydrogenation

text: . This research culminated in the publication of his book Anhydrous Aluminum Chloride in Organic Chemistry in 1941.

text: In S2 reactions, there are a few conditions that affect the rate of the reaction.  First of all, the 2 in S2 implies that there are two concentrations of substances that affect the rate of reaction: substrate and nucleophile.  The rate equation for this reaction would be Rate=k[Sub][Nuc].  For a S2 reaction, an aprotic solvent is best, such as acetone, DMF, or DMSO.  Aprotic solvents do not add protons (H+) ions into solution; if protons were present in S2 reactions, they would react with the nucleophile and severely limit the reaction rate.  Since this reaction occurs in one step, steric effects drive the reaction speed. In the intermediate step, the nucleophile is 180 degrees from the leaving group and the stereochemistry is inverted as the nucleophile bonds to make the product.  Also, because the intermediate is partially bonded to the nucleophile and leaving group, there is no time for the substrate to rearrange itself: the nucleophile will bond to the same carbon that the leaving group was attached to.  A final factor that affects reaction rate is nucleophilicity; the nucleophile must attack an atom other than a hydrogen.

text: In S2 reactions, there are a few conditions that affect the rate of the reaction.  First of all, the 2 in S2 implies that there are two concentrations of substances that affect the rate of reaction: substrate and nucleophile.  The rate equation for this reaction would be Rate=k[Sub][Nuc].  For a S2 reaction, an

text: aprotic solvent

text: is best, such as acetone, DMF, or DMSO.  Aprotic solvents do not add protons (H+) ions into solution; if protons were present in S2 reactions, they would react with the nucleophile and severely limit the reaction rate.  Since this reaction occurs in one step,

text: steric effects

text: drive the reaction speed. In the intermediate step, the nucleophile is 180 degrees from the leaving group and the stereochemistry is inverted as the nucleophile bonds to make the product.  Also, because the intermediate is partially bonded to the nucleophile and leaving group, there is no time for the substrate to rearrange itself: the nucleophile will bond to the same carbon that the leaving group was attached to.  A final factor that affects reaction rate is nucleophilicity; the nucleophile must attack an atom other than a hydrogen.

text: The concentration of reactants and products in autocatalytic reactions follow the logistic function.

text: The concentration of reactants and products in

text: autocatalytic reactions

text: follow the logistic function.

text: Unoptimized reactions typically use 10-15 mol% of palladium.  In optimized reactions, catalyst loadings can be on the order of 0.1 mol % or below. Palladium nano clusters have been found to catalyze coupling reactions with catalyst loadings as low as parts per billion, however such systems typically do not maintain catalytic activity as long as well defined ligated catalysts. Many exotic ligands and chiral catalysts have been reported, but they are largely not available commercially, and do not find widespread use. Much work is being done on replacing the phosphine ligands with other classes, such as Arduengo-type carbene complexes, as the phosphine ligands are typically oxygen sensitive (easily oxidized) and must be handled under an inert atmosphere. Phosphines are labile, sometimes requiring additional ligand. For example, Pd(PPh) would be supplemented with PPh to keep the palladium coordinated despite loss of the labile phosphine ligands.

text: Unoptimized reactions typically use 10-15 mol% of palladium.  In optimized reactions, catalyst loadings can be on the order of 0.1 mol % or below. Palladium nano clusters have been found to catalyze coupling reactions with catalyst loadings as low as parts per billion, however such systems typically do not maintain catalytic activity as long as well defined ligated catalysts. Many exotic ligands and chiral catalysts have been reported, but they are largely not available commercially, and do not find widespread use. Much work is being done on replacing the phosphine ligands with other classes, such as Arduengo-type

text: carbene

text: complexes, as the phosphine ligands are typically oxygen sensitive (easily oxidized) and must be handled under an inert atmosphere. Phosphines are

text: labile

text: , sometimes requiring additional ligand. For example, Pd(PPh) would be supplemented with PPh to keep the palladium coordinated despite loss of the labile phosphine ligands.

text: In the related condensation reaction water is released from two different reactants.

text: In the related

text: condensation reaction

text: water is released from two different reactants.

text: Glass and metal can bond together by purely mechanical means, which usually gives weaker joints, or by chemical interaction, where the oxide layer on the metal surface forms a strong bond with the glass. The acid-base reactions are main causes of interaction between glass-metal in the presence of metal oxides on the surface of metal. After complete dissolution of the surface oxides into the glass, further progress of interaction depends on the oxygen activity at the interface. The oxygen activity can be increased by diffusion of molecular oxygen through some defects like cracks. Also, reduction of the thermodynamically less stable components in the glass (and releasing the oxygen ions) can increase the oxygen activity at the interface. In other words, the redox reactions are main causes of interaction between glass-metal in the absence of metal oxides on the surface of metal.

text: Glass and metal can bond together by purely mechanical means, which usually gives weaker joints, or by chemical interaction, where the oxide layer on the metal surface forms a strong bond with the glass. The

text: acid-base reaction

text: s are main causes of interaction between glass-metal in the presence of metal oxides on the surface of metal. After complete dissolution of the surface oxides into the glass, further progress of interaction depends on the oxygen

text: activity

text: at the interface. The oxygen

text: activity

text: can be increased by diffusion of

text: molecular oxygen

text: through some defects like cracks. Also, reduction of the thermodynamically less stable components in the glass (and releasing the oxygen ions) can increase the oxygen

text: activity

text: at the interface. In other words, the

text: redox

text: reactions are main causes of interaction between glass-metal in the absence of metal oxides on the surface of metal.

text: The catalyst is most commonly phosphoric acid, adsorbed onto a porous support such as silica gel or diatomaceous earth. This catalyst was first used for large-scale ethanol production by the Shell Oil Company in 1947. The reaction is carried out in the presence of high pressure steam at  where a 1.0:0.6 ethylene to steam ratio is maintained. In the U.S., this process was used on an industrial scale by Union Carbide Corporation and others, but now only LyondellBasell uses it commercially.

text: The catalyst is most commonly

text: phosphoric acid

text: adsorbed

text: onto a porous support such as

text: silica gel

text: or

text: diatomaceous earth

text: . This catalyst was first used for large-scale ethanol production by the

text: Shell Oil Company

text: in 1947. The reaction is carried out in the presence of high pressure steam at  where a 1.0:0.6 ethylene to steam ratio is maintained. In the U.S., this process was used on an industrial scale by

text: Union Carbide Corporation

text: and others, but now only

text: LyondellBasell

text: uses it commercially.

text: Beside high mechanical energy, higher cleaning temperatures are one of the most effective methods of improving the cleaning results in a parts washer. In general, a 10 to 15 °F (5 to 8 °C) rise doubles the chemical reaction of the detergent.  The increased chemical reaction between the greases and oils and the detergent delivers faster cleaning cycles and cleaner parts.  Additionally, all greases and oils exhibit a lower viscosity at higher temperatures. Cleaning solution temperatures of  and above softens or melts most oils and greases causing them to flow like water so they are easily removed resulting in faster cleaning, better results and cleaner parts. Many parts washers are not capable of maintaining this operating temperature due to the lack of amply heating systems.  Additionally, careful design is required of the pumping system so it can pull in and deliver cleaning solution at temperatures that approach boiling in the parts washer. All centrifugal pumps require a net positive suction head (NPSHr) in order to be able to pump solution.  As the temperature of the solution approaches the NPSHr, the pump stops pumping because the cleaning solution flashes to steam in the pump intake.  Careful design of the pump is required to minimize NPSHr and allow pumping of high temperature cleaning solution.

text: Beside high mechanical energy, higher cleaning temperatures are one of the most effective methods of improving the cleaning results in a parts washer. In general, a 10 to 15 °F (5 to 8 °C) rise doubles the

text: chemical reaction

text: of the detergent.  The increased chemical reaction between the greases and oils and the detergent delivers faster cleaning cycles and cleaner parts.  Additionally, all greases and oils exhibit a lower

text: viscosity

text: at higher temperatures. Cleaning solution temperatures of  and above softens or melts most oils and greases causing them to flow like water so they are easily removed resulting in faster cleaning, better results and cleaner parts. Many parts washers are not capable of maintaining this

text: operating temperature

text: due to the lack of amply heating systems.  Additionally, careful design is required of the pumping system so it can pull in and deliver cleaning solution at temperatures that approach boiling in the parts washer. All

text: centrifugal pump

text: s require a

text: net positive suction head

text: (NPSHr) in order to be able to pump solution.  As the temperature of the solution approaches the NPSHr, the pump stops pumping because the cleaning solution flashes to steam in the pump intake.  Careful design of the pump is required to minimize NPSHr and allow pumping of high temperature cleaning solution.

text: Polysilicon layers can be deposited using 100% silane at a pressure of  or with 20–30% silane (diluted in nitrogen) at the same total pressure. Both of these processes can deposit polysilicon on 10–200 wafers per run, at a rate of 10–20 nm/min and with thickness uniformities of ±5%. Critical process variables for polysilicon deposition include temperature, pressure, silane concentration, and dopant concentration. Wafer spacing and load size have been shown to have only minor effects on the deposition process. The rate of polysilicon deposition increases rapidly with temperature, since it follows Arrhenius behavior, that is deposition rate = A·exp(–qE/kT) where q is electron charge and k is the Boltzmann constant. The activation energy (E) for polysilicon deposition is about 1.7 eV. Based on this equation, the rate of polysilicon deposition increases as the deposition temperature increases. There will be a minimum temperature, however, wherein the rate of deposition becomes faster than the rate at which unreacted silane arrives at the surface. Beyond this temperature, the deposition rate can no longer increase with temperature, since it is now being hampered by lack of silane from which the polysilicon will be generated. Such a reaction is then said to be 'mass-transport-limited.' When a polysilicon deposition process becomes mass-transport-limited, the reaction rate becomes dependent primarily on reactant concentration, reactor geometry, and gas flow.

text: Polysilicon layers can be deposited using 100% silane at a pressure of  or with 20–30% silane (diluted in nitrogen) at the same total pressure. Both of these processes can deposit polysilicon on 10–200 wafers per run, at a rate of 10–20 nm/min and with thickness uniformities of ±5%. Critical process variables for polysilicon deposition include temperature, pressure, silane concentration, and dopant concentration. Wafer spacing and load size have been shown to have only minor effects on the deposition process. The rate of polysilicon deposition increases rapidly with temperature, since it follows

text: Arrhenius

text: behavior, that is deposition rate = A·exp(–qE/kT) where q is electron charge and k is the

text: Boltzmann constant

text: . The activation energy (E) for polysilicon deposition is about 1.7 eV. Based on this equation, the rate of polysilicon deposition increases as the deposition temperature increases. There will be a minimum temperature, however, wherein the rate of deposition becomes faster than the rate at which unreacted silane arrives at the surface. Beyond this temperature, the deposition rate can no longer increase with temperature, since it is now being hampered by lack of silane from which the polysilicon will be generated. Such a reaction is then said to be 'mass-transport-limited.' When a polysilicon deposition process becomes mass-transport-limited, the reaction rate becomes dependent primarily on reactant concentration, reactor geometry, and gas flow.

text: Marcus theory is a theory originally developed by Rudolph A. Marcus, starting in 1956, to explain the rates of electron transfer reactions – the rate at which an electron can move or jump from one chemical species (called the electron donor) to another (called the electron acceptor). It was originally formulated to address outer sphere electron transfer reactions, in which the two chemical species only change in their charge with an electron jumping (e.g. the oxidation of an ion like Fe/Fe), but do not undergo large structural changes. It was extended to include inner sphere electron transfer contributions, in which a change of distances or geometry in the solvation or coordination shells of the two chemical species is taken into account (the Fe-O distances in Fe(HO) and Fe(HO) are different).

text: Marcus theory is a theory originally developed by

text: Rudolph A. Marcus

text: , starting in 1956, to explain the

text: rates

text: of

text: electron transfer

text: reactions – the rate at which an

text: electron

text: can move or jump from one

text: chemical species

text: (called the

text: electron donor

text: ) to another (called the

text: electron acceptor

text: ). It was originally formulated to address

text: outer sphere electron transfer

text: reactions, in which the two chemical species only change in their

text: charge

text: with an electron jumping (e.g. the oxidation of an ion like Fe/Fe), but do not undergo large structural changes. It was extended to include

text: inner sphere electron transfer

text: contributions, in which a change of distances or geometry in the

text: solvation

text: or

text: coordination shells

text: of the two chemical species is taken into account (the Fe-O distances in Fe(HO) and Fe(HO) are different).

text: is the probability that any given collision will result in a reaction. It can be seen that either increasing the temperature or decreasing the activation energy (for example through the use of catalysts) will result in an increase in rate of reaction.

text: is the probability that any given collision will result in a reaction. It can be seen that either increasing the temperature or decreasing the activation energy (for example through the use of

text: catalyst

text: s) will result in an increase in rate of reaction.

text: is the density of primary ions in absence of reactant molecules in the buffer gas,  is the reaction rate constant and  is the average time the ions need to pass the reaction region. With a PTR-MS instrument the number of product and of primary ions can be measured, the reaction rate constant can be found in literature for most substances and the reaction time can be derived from the set instrument parameters. Therefore the absolute concentration of trace constituents

text: is the density of primary ions in absence of reactant molecules in the buffer gas,  is the

text: reaction rate constant

text: and  is the average time the ions need to pass the reaction region. With a PTR-MS instrument the number of product and of primary ions can be measured, the reaction rate constant can be found in literature for most substances and the reaction time can be derived from the set instrument parameters. Therefore the absolute

text: concentration

text: of trace constituents

text: As described above, same-excess experiments are conducted with two or more experiments holding the excess, (e) constant while changing the absolute concentrations of the substrates (in this case, the catalyst is also treated as a substrate.) Note that this construction causes the number of equivalents and therefore the mole percentage of each reagent/catalyst to differ between reactions. These experiments enable one to artificially "enter" the reaction at any point, as the initial concentrations of one experiment (the intercepting reaction) are chosen to map directly onto the anticipated concentrations at some intermediate time, t, in another (the parent reaction). One would expect the reaction progress, described by the rate vs. substrate concentration plots detailed above, to map directly onto each other from that interception point onward. This will hold true, however, only if the rate of the reaction is not altered by changes to the active substrate/catalyst concentration (such as by catalyst activation, catalyst deactivation, or product inhibition) before that interception.

text: Products are the species formed from chemical reactions. During a chemical reaction reactants are transformed into products after passing through a high energy transition state. This process results in the consumption of the reactants.  It can be a spontaneous reaction or mediated by catalysts which lower the energy of the transition state, and by solvents which provide the chemical environment necessary for the reaction to take place. When represented in chemical equations products are by convention drawn on the right-hand side, even in the case of reversible reactions. The properties of products such as their energies help determine several characteristics of a chemical reaction such as whether the reaction is exergonic or endergonic. Additionally the properties of a product can make it easier to extract and purify following a chemical reaction, especially if the product has a different state of matter than the reactants. Reactants are molecular materials used to create chemical reactions. The atoms aren't created or destroyed. The materials are reactive and reactants are rearranging during a chemical reaction. Here is an example of reactants: CH4 + O2. A non-example is CO2 + H2O or "energy".

text: Products are the species formed from

text: chemical reaction

text: s. During a chemical reaction

text: reactants

text: are transformed into products after passing through a high energy

text: transition state

text: . This process results in the consumption of the reactants.  It can be a

text: spontaneous reaction

text: or mediated by

text: catalyst

text: s which lower the energy of the transition state, and by

text: solvent

text: s which provide the chemical environment necessary for the reaction to take place. When represented in

text: chemical equation

text: s products are by convention drawn on the right-hand side, even in the case of

text: reversible reaction

text: s. The properties of products such as their energies help determine several characteristics of a chemical reaction such as whether the reaction is

text: exergonic

text: or

text: endergonic

text: . Additionally the properties of a product can make it easier to extract and purify following a chemical reaction, especially if the product has a different

text: state of matter

text: than the reactants. Reactants are molecular materials used to create chemical reactions. The atoms aren't created or destroyed. The materials are reactive and reactants are rearranging during a chemical reaction. Here is an example of reactants: CH4 + O2. A non-example is CO2 + H2O or "energy".

text: Reactions generally accelerate when heat is applied. Where a reaction is exothermic, the rate of the reaction may initially be low. As the reaction proceeds, heat is generated, and the rate of reaction increases. This type of reaction often exhibits an induction period as well.

text: Reactions generally accelerate when heat is applied. Where a reaction is

text: exothermic

text: , the rate of the reaction may initially be low. As the reaction proceeds, heat is generated, and the rate of reaction increases. This type of reaction often exhibits an induction period as well.

text: A large fraction of the rocket engines in use today are chemical rockets; that is, they obtain the energy needed to generate thrust by chemical reactions to create a hot gas that is expanded to produce thrust. A significant limitation of chemical propulsion is that it has a relatively low specific impulse (Isp), which is the ratio of the thrust produced to the mass of propellant needed at a certain rate of flow.

text: A large fraction of the

text: rocket engine

text: s in use today are

text: chemical rockets

text: ; that is, they obtain the energy needed to generate thrust by

text: chemical reactions

text: to create a hot gas that is expanded to produce

text: thrust

text: . A significant limitation of

text: chemical propulsion

text: is that it has a relatively low

text: specific impulse

text: (Isp), which is the

text: ratio

text: of the thrust produced to the

text: mass of propellant

text: needed at a certain

text: rate of flow

text: The initial amounts of reactants determine the distance from chemical equilibrium of the system. The greater the initial concentrations the further the system is from equilibrium. As the initial concentration increases, an abrupt change in order occurs. This abrupt change is known as phase transition. At the phase transition, fluctuations in macroscopic quantities, such as chemical concentrations, increase as the system oscillates between the more ordered state (lower entropy, such as ice) and the more disordered state (higher entropy, such as liquid water). Also, at the phase transition, macroscopic equations, such as the rate equations, fail. Rate equations can be derived from microscopic considerations. The derivations typically rely on a mean field theory approximation to microscopic dynamical equations. Mean field theory breaks down in the presence of large fluctuations (see Mean field theory article for a discussion).  Therefore, since large fluctuations occur in the neighborhood of a phase transition, macroscopic equations, such as rate equations, fail. As the initial concentration increases further, the system settles into an ordered state in which fluctuations are again small. (see Prigogine reference)

text: The initial amounts of reactants determine the distance from chemical equilibrium of the system. The greater the initial concentrations the further the system is from equilibrium. As the initial concentration increases, an abrupt change in

text: order

text: occurs. This abrupt change is known as

text: phase transition

text: . At the phase transition, fluctuations in macroscopic quantities, such as chemical concentrations, increase as the system oscillates between the more ordered state (lower entropy, such as ice) and the more disordered state (higher entropy, such as liquid water). Also, at the phase transition, macroscopic equations, such as the rate equations, fail. Rate equations can be derived from microscopic considerations. The derivations typically rely on a

text: mean field theory

text: approximation to microscopic dynamical equations. Mean field theory breaks down in the presence of large fluctuations (see

text: Mean field theory

text: article for a discussion).  Therefore, since large fluctuations occur in the neighborhood of a phase transition, macroscopic equations, such as rate equations, fail. As the initial concentration increases further, the system settles into an ordered state in which fluctuations are again small. (see Prigogine reference)

text: Carbohydrates are reactants in many organic reactions. For example:

text: Carbohydrates are reactants in many

text: organic reaction

text: s. For example:

text: A mixture of fuel and air ignites when the concentration and temperature of reactants is sufficiently high. The concentration and/or temperature can be increased in several different ways:

text: Although Chapman took a keen interest in his students, research was his main priority. Chapman had a particular interest in the photochemical reaction of hydrogen and chlorine, establishing that minute traces of impurities caused unexpected consequences.  He suggested the steady state hypothesis in 1913.  He discovered that the interruption of light by a rotating sector caused the rate of the reaction to vary with the frequency of the sector and, in 1926, he was the first to apply this theory to measure the 'mean life' of a reaction intermediate.  Other areas of interest were the theory of detonation in gases (the subject of an important paper that Chapman published in 1899, with reliable calculations of detonation speeds; the theory is still known as the Chapman-Jouget treatment) and the distribution of ions at a charged surface (with the name of the Gouy-Chapman layer being given to the surface layer that he envisaged).

text: Although Chapman took a keen interest in his students, research was his main priority. Chapman had a particular interest in the

text: photochemical

text: reaction of

text: hydrogen

text: and

text: chlorine

text: , establishing that minute traces of impurities caused unexpected consequences.  He suggested the

text: steady state

text: hypothesis in 1913.  He discovered that the interruption of light by a rotating sector caused the rate of the reaction to vary with the frequency of the sector and, in 1926, he was the first to apply this theory to measure the 'mean life' of a reaction intermediate.  Other areas of interest were the theory of detonation in gases (the subject of an important paper that Chapman published in 1899, with reliable calculations of detonation speeds; the theory is still known as the Chapman-Jouget treatment) and the distribution of ions at a charged surface (with the name of the Gouy-Chapman layer being given to the surface layer that he envisaged).

text: The liquid feed (at the bottom left in the diagram) is pumped up to the reaction pressure (5–45 atm) and is joined by a stream of hydrogen-rich recycle gas. The resulting liquid–gas mixture is preheated by flowing through a heat exchanger. The preheated feed mixture is then totally vaporized and heated to the reaction temperature (495–520 °C) before the vaporized reactants enter the first reactor. As the vaporized reactants flow through the fixed bed of catalyst in the reactor, the major reaction is the dehydrogenation of naphthenes to aromatics (as described earlier herein) which is highly endothermic and results in a large temperature decrease between the inlet and outlet of the reactor. To maintain the required reaction temperature and the rate of reaction, the vaporized stream is reheated in the second fired heater before it flows through the second reactor. The temperature again decreases across the second reactor and the vaporized stream must again be reheated in the third fired heater before it flows through the third reactor. As the vaporized stream proceeds through the three reactors, the reaction rates decrease and the reactors therefore become larger.  At the same time, the amount of reheat required between the reactors becomes smaller. Usually, three reactors are all that is required to provide the desired performance of the catalytic reforming unit.

text: The liquid feed (at the bottom left in the diagram) is pumped up to the reaction pressure (5–45 atm) and is joined by a stream of hydrogen-rich recycle gas. The resulting liquid–gas mixture is preheated by flowing through a

text: heat exchanger

text: . The preheated feed mixture is then totally

text: vaporized

text: and heated to the reaction temperature (495–520 °C) before the vaporized reactants enter the first reactor. As the vaporized reactants flow through the fixed bed of catalyst in the reactor, the major reaction is the dehydrogenation of naphthenes to aromatics (as described earlier herein) which is highly

text: endothermic

text: and results in a large temperature decrease between the inlet and outlet of the reactor. To maintain the required reaction temperature and the rate of reaction, the vaporized stream is reheated in the second fired heater before it flows through the second reactor. The temperature again decreases across the second reactor and the vaporized stream must again be reheated in the third fired heater before it flows through the third reactor. As the vaporized stream proceeds through the three reactors, the reaction rates decrease and the reactors therefore become larger.  At the same time, the amount of reheat required between the reactors becomes smaller. Usually, three reactors are all that is required to provide the desired performance of the catalytic reforming unit.

text: The velocities of cricket bowlers vary between . In professional cricket, a bowler in the 40–60 mph range would be said to be a slow bowler, in the 60–80 mph range a medium pace bowler, and a bowler 80 mph+ a fast bowler. In the amateur game, these distinctions would be approximately 10 mph slower. Many professional fast bowlers are able to reach speeds of over 85 mph, with a handful of bowlers in the world able to bowl at 95 mph+. The ability to react to a cricket ball travelling at 85 mph is a skill that only professional and high level amateur cricketers possess. The pace of a bowler not only challenges the reaction speed of the batsman, but also his physical courage. Fast bowlers are able to exploit this by bowling bouncers, either regularly or as an occasional surprise delivery.

text: The experimental determination of reaction rates involves measuring how the concentrations of reactants or products change over time. For example, the concentration of a reactant can be measured by spectrophotometry at a wavelength where no other reactant or product in the system absorbs light.

text: The experimental determination of reaction rates involves measuring how the concentrations of reactants or products change over time. For example, the concentration of a reactant can be measured by

text: spectrophotometry

text: at a wavelength where no other reactant or product in the system absorbs light.

text: Gillespie's original derivation of the SSA began by considering how chemical reactions actually occur in a well-stirred dilute gas.  Reasoning from physics (and not by heuristically extrapolating deterministic reaction rates to a stochastic context), he showed that the probability that a specific reaction will occur in the next very small time dt could be written as an explicit function of the current species populations multiplied by dt.  From that result he deduced, using only the laws of probability, an exact formula for the joint probability density function p(τ,j) of the {time τ to the next reaction event} and the {index j of that reaction}.  The SSA consists of first generating random values for τ and j according to p(τ,j), and then actualizing the next reaction accordingly.  The generating step of the SSA can be accomplished using any of several different methods, and Gillespie's original paper presented two:  the "direct method", which follows from a straightforward application of the well known Monte Carlo inversion method for generating random numbers; and the "first-reaction method", which is less straightforward but mathematically equivalent.  Later workers derived additional methods for generating random numbers according to Gillespie's function p(τ,j) which offer computational advantages in various specific situations. Gillespie's original derivation of the SSA applied only to a well-stirred dilute gas.  It was widely assumed/hoped that the SSA would also apply when the reactant molecules are solute molecules in a well-stirred dilute solution, a case more appropriate to cellular chemistry.  In fact it does, but that was not definitively established until 2009.  The SSA is one component of stochastic chemical kinetics, a field that Gillespie played a major role in developing and clarifying through his later publications.

text: The rate expressions given in the 1864 paper could not be integrated, so they were simplified as follows. The chemical force was assumed to be directly proportional to the product of the active masses of the reactants.

text: 1. Single step reaction between the reactants excluding the intermediate steps.

text: Rhenium in the form of rhenium-platinum alloy is used as catalyst for catalytic reforming, which is a chemical process to convert petroleum refinery naphthas with low octane ratings into high-octane liquid products. Worldwide, 30% of catalysts used for this process contain rhenium. The olefin metathesis is the other reaction for which rhenium is used as catalyst. Normally ReO on alumina is used for this process. Rhenium catalysts are very resistant to chemical poisoning from nitrogen, sulfur and phosphorus, and so are used in certain kinds of hydrogenation reactions.

text: Rhenium in the form of rhenium-platinum alloy is used as catalyst for

text: catalytic reforming

text: , which is a chemical process to convert petroleum refinery

text: naphthas

text: with low

text: octane rating

text: s into high-octane liquid products. Worldwide, 30% of catalysts used for this process contain rhenium. The

text: olefin metathesis

text: is the other reaction for which rhenium is used as catalyst. Normally ReO on

text: alumina

text: is used for this process. Rhenium catalysts are very resistant to

text: chemical poisoning

text: from nitrogen, sulfur and phosphorus, and so are used in certain kinds of hydrogenation reactions.

text: The uncatalyzed reaction is rather slow, and a high X is not readily attained.  In the presence of a catalyst, there is an acceleration of the rate, and the kinetic expression is altered to

text: The equilibrium expression above is a function of the concentrations [A], [B] etc. of the chemical species in equilibrium. The equilibrium constant value can be determined if any one of these concentrations can be measured. The general procedure is that the concentration in question is measured for a series of solutions with known analytical concentrations of the reactants. Typically, a titration is performed with one or more reactants in the titration vessel and one or more reactants in the burette. Knowing the analytical concentrations of reactants initially in the reaction vessel and in the burette, all analytical concentrations can be derived as a function of the volume (or mass) of titrant added.

text: The equilibrium expression above is a function of the

text: concentration

text: s [A], [B] etc. of the chemical species in equilibrium. The equilibrium constant value can be determined if any one of these concentrations can be measured. The general procedure is that the concentration in question is measured for a series of solutions with known

text: analytical concentration

text: s of the reactants. Typically, a

text: titration

text: is performed with one or more reactants in the titration vessel and one or more reactants in the burette. Knowing the analytical concentrations of reactants initially in the reaction vessel and in the burette, all analytical concentrations can be derived as a function of the volume (or mass) of titrant added.

text: Depending on the concentration of the reactant the rate changes:

text: Packed bed reactors can be used in chemical reaction. These reactors are tubular and are filled with solid catalyst particles, most often used to catalyze gas reactions. The chemical reaction takes place on the surface of the catalyst. The advantage of using a packed bed reactor is the higher conversion per weight of catalyst than other catalytic reactors. The conversion is based on the amount of the solid catalyst rather than the volume of the reactor.

text: Packed bed reactors can be used in chemical reaction. These reactors are tubular and are filled with solid catalyst particles, most often used to catalyze gas reactions. The chemical reaction takes place on the surface of the

text: catalyst

text: . The advantage of using a packed bed reactor is the higher conversion per weight of catalyst than other catalytic reactors. The conversion is based on the amount of the solid catalyst rather than the volume of the reactor.

text: Compared to basic chemical vapour deposition, in ALE (ALD), chemical reactants are pulsed alternatively in a reaction chamber and then chemisorb in a saturating manner on the surface of the substrate, forming a chemisorbed monolayer. This is clever because the reaction is easy to set up and it does not require many restrictions over the reactants, allowing the use of a wide range of materials.

text: Compared to basic

text: chemical vapour deposition

text: , in ALE (ALD), chemical reactants are pulsed alternatively in a reaction chamber and then chemisorb in a saturating manner on the surface of the substrate, forming a chemisorbed monolayer. This is clever because the reaction is easy to set up and it does not require many restrictions over the reactants, allowing the use of a wide range of materials.

text: A modification of canonical variational transition state theory in which, for energies below the threshold energy, the position of the dividing surface is taken to be that of the microcanonical threshold energy. This forces the contributions to rate constants to be zero if they are below the threshold energy. A compromise dividing surface is then chosen so as to minimize the contributions to the rate constant made by reactants having higher energies.

text: The olefin feed to an alkylation unit generally originates from a FCCU and contains butene, isobutene, and possibly propene and/or amylenes. The olefin feed is also likely to contain diluents (such as propane, n-butane, and n-pentane), noncondensables (such as ethane and hydrogen) and contaminants. Diluants in principle have no effect on the reaction of alkylation but occupy a portion of the reactor and can influence the yield of secondary reactions of polymerisation and of undesired organofluorine side products. Incondensable are from a chemical perspective similar to diluents but they do not condense at the pressure and temperature of the process, and therefore they concentrate to a point that must be vented. Contaminants are compounds that react with and/or dilute the sulfuric acid catalyst. They increase acid consumption and contribute to produce undesirable reaction products and increase polymer formation. Common contaminants are water, methanol and ethanol.

text: The olefin feed to an alkylation unit generally originates from a FCCU and contains

text: butene

text: isobutene

text: , and possibly

text: propene

text: and/or

text: amylene

text: s. The olefin feed is also likely to contain diluents (such as

text: propane

text: n-butane

text: , and

text: n-pentane

text: ), noncondensables (such as ethane and hydrogen) and contaminants. Diluants in principle have no effect on the reaction of alkylation but occupy a portion of the reactor and can influence the yield of secondary reactions of polymerisation and of undesired organofluorine side products. Incondensable are from a chemical perspective similar to diluents but they do not condense at the pressure and temperature of the process, and therefore they concentrate to a point that must be vented. Contaminants are compounds that react with and/or dilute the sulfuric acid catalyst. They increase acid consumption and contribute to produce undesirable reaction products and increase polymer formation. Common contaminants are

text: water

text: methanol

text: and

text: ethanol

text: In addition to simply slowing the reaction, a change in catalyst resting state over the course of the reaction may result in competing paths or processes. Multiple mechanisms may be present to access the product, in which case the order in catalyst or substrate may change depending on the conditions or point in the reaction. A particularly useful probe for changes in reaction mechanism involves examination of the normalized reaction rate vs. catalyst loading at multiple, fixed conversion points. Note that the normalized reaction rate:

text: An electrocatalyst is a catalyst that participates in electrochemical reactions.  Catalyst materials modify and increase the rate of chemical reactions without being consumed in the process.  Electrocatalysts are a specific form of catalysts that function at electrode surfaces or may be the electrode surface itself.  An electrocatalyst can be heterogeneous such as a platinum surface or nanoparticles,  or homogeneous like a coordination complex or enzyme.  The electrocatalyst assists in transferring electrons between the electrode and reactants, and/or facilitates an intermediate chemical transformation described by an overall half-reaction.

text: An electrocatalyst is a

text: catalyst

text: that participates in

text: electrochemical reactions

text: .  Catalyst materials modify and increase the rate of chemical reactions without being consumed in the process.  Electrocatalysts are a specific form of catalysts that function at

text: electrode

text: surfaces or may be the electrode surface itself.  An electrocatalyst can be

text: heterogeneous

text: such as a platinum surface or

text: nanoparticles

text: ,  or

text: homogeneous

text: like a

text: coordination complex

text: or

text: enzyme

text: .  The electrocatalyst assists in transferring electrons between the electrode and reactants, and/or facilitates an intermediate chemical transformation described by an overall

text: half-reaction

text: Part of the reason for the importance of this particular piece in Eliot's body of work is the position it holds as successor to an earlier (and probably better known) effort at defining the critical endeavour, Tradition and the Individual Talent. In that earlier piece (first published in 1919), Eliot made famous use of a metaphor drawn from chemistry to describe the process of "depersonalization" that Eliot claimed to be a necessary condition of poetic creation. In this analogy, Eliot compares the poet him- or herself to a catalyst, whose presence causes "feelings" and "emotions" to react with one another and combine in ways not possible without the poet's mind.

text: Part of the reason for the importance of this particular piece in Eliot's body of work is the position it holds as successor to an earlier (and probably better known) effort at defining the critical endeavour,

text: Tradition and the Individual Talent

text: . In that earlier piece (first published in 1919), Eliot made famous use of a

text: metaphor

text: drawn from

text: chemistry

text: to describe the process of "depersonalization" that Eliot claimed to be a necessary condition of poetic creation. In this analogy, Eliot compares the poet him- or herself to a

text: catalyst

text: , whose presence causes "feelings" and "emotions" to react with one another and combine in ways not possible without the poet's

text: mind

text: When performing kinetic or thermodynamic studies, it is often useful to have one or more reactants in abundance, as it allows their concentrations to be treated as constants (or parameters) rather than as variables.

text: When performing

text: kinetic

text: or

text: thermodynamic

text: studies, it is often useful to have one or more reactants in abundance, as it allows their concentrations to be treated as

text: constant

text: s (or

text: parameter

text: s) rather than as

text: variables

text: In some cases, a highly active catalyst can lead to undesirable secondary reactions with desired product.  In some of these cases, the addition of a small amount of a catalyst poison increase the yield of the desired product by lower the catalyst activity. For example, in the classical "Rosenmund reduction" of an acyl chloride to the corresponding aldehyde, the palladium catalyst (over barium sulfate or calcium carbonate) is intentionally poisoned by the addition of sulfur or quinoline in order to lower the catalyst activity and thereby prevent further reduction of the aldehyde product to yield a primary alcohol.  In the case of Lindlar's catalyst, palladium is poisoned with a lead salt to allow reduction of an alkyne to the corresponding alkene while preventing reduction of the alkene product to the corresponding alkane.

text: In some cases, a highly active catalyst can lead to undesirable secondary reactions with desired product.  In some of these cases, the addition of a small amount of a catalyst poison increase the yield of the desired product by lower the catalyst activity. For example, in the classical "

text: Rosenmund reduction

text: " of an

text: acyl chloride

text: to the corresponding

text: aldehyde

text: , the

text: palladium

text: catalyst (over

text: barium sulfate

text: or

text: calcium carbonate

text: ) is intentionally poisoned by the addition of

text: sulfur

text: or

text: quinoline

text: in order to lower the catalyst activity and thereby prevent further reduction of the aldehyde product to yield a primary alcohol.  In the case of

text: Lindlar's catalyst

text: palladium

text: is poisoned with a

text: lead

text: salt to allow reduction of an alkyne to the corresponding alkene while preventing reduction of the alkene product to the corresponding alkane.

text: stoichiometric coefficient.  The reaction rate, r, is generally dependent on the reactant concentration and the rate constant (k). The rate constant can be determined by using a known empirical reaction rates that is adjusted for temperature using the Arrhenius temperature dependence.  Generally, as the temperature increases so does the rate at which the reaction occurs. Residence time,

text: stoichiometric coefficient

text: .  The reaction rate, r, is generally dependent on the reactant concentration and the rate constant (k). The rate constant can be determined by using a known empirical reaction rates that is adjusted for temperature using the

text: Arrhenius temperature dependence

text: .  Generally, as the temperature increases so does the rate at which the reaction occurs.

text: Residence time

text: is the net mass production rate in chemical reactions,

text: Typical catalysts are noble metals, Ni or Ni alloys. In addition, a group of researchers in China investigated the use of activated carbon as an alternative catalyst.

text: Many techniques have been developed to measure the rates of radical reactions. The two possible ways to measure the reaction rates are direct and indirect approaches. Direct approaches such as the rotating sector method have restrictions that hinder their expansion or application to the wide variety of types of radical reactions of chemical interest. In addition, direct methods such as flash photolysis and pulse radiolysis require a relatively large amount of time and expensive equipment. With an indirect approach, one can still obtain relative or absolute rate constants without the need for instruments or equipment beyond those normally needed for the reaction being studied.

text: Many techniques have been developed to measure the rates of radical reactions. The two possible ways to measure the reaction rates are direct and indirect approaches. Direct approaches such as the

text: rotating sector method

text: have restrictions that hinder their expansion or application to the wide variety of types of radical reactions of chemical interest. In addition, direct methods such as

text: flash photolysis

text: and

text: pulse radiolysis

text: require a relatively large amount of time and expensive equipment. With an indirect approach, one can still obtain relative or absolute rate constants without the need for instruments or equipment beyond those normally needed for the reaction being studied.

text: The Gattermann reaction, (also known as the Gattermann aldehyde synthesis)  is a chemical reaction in which aromatic compounds are formylated by hydrogen cyanide in the presence of a Friedel–Crafts catalyst (e.g. AlCl). It is named for the German chemist Ludwig Gattermann and is similar to the Friedel-Crafts reaction.

text: The Gattermann reaction, (also known as the Gattermann aldehyde synthesis)  is a chemical reaction in which aromatic compounds are

text: formylated

text: by

text: hydrogen cyanide

text: in the presence of a

text: Friedel–Crafts

text: catalyst (e.g.

text: AlCl

text: ). It is named for the German chemist

text: Ludwig Gattermann

text: and is similar to the

text: Friedel-Crafts reaction

text: Raphael D. Levine is known for his contributions in the modern theory of chemically reactive collisions and unimolecular reactions. He has played a major role in the application of the principles of quantum mechanics to the description of physical change in a reaction from a microscopic point of view, introducing many new concepts and terms which became standard to this area. His major works include the quantum theory of absolute rates, the first quantal treatment of molecular photodissociation, elucidation of the role of resonances in reactive molecular collisions, the theory of collision- induced dissociation, and the foundations of dynamical stereochemistry.

text: Van 't Hoff studied chemical dynamics and published in 1884 his famous "Etudes de dynamique chimique". In 1901 he was awarded by the first Nobel Prize in Chemistry "in recognition of the extraordinary services he has rendered by the discovery of the laws of chemical dynamics and osmotic pressure in solutions". After van 't Hoff, chemical kinetics deals with the experimental determination of reaction rates from which rate laws and rate constants are derived. Relatively simple rate laws exist for zero order reactions (for which reaction rates are independent of concentration), first order reactions, and second order reactions, and can be derived for others. Elementary reactions follow the law of mass action, but the rate law of stepwise reactions has to be derived by combining the rate laws of the various elementary steps, and can become rather complex. In consecutive reactions, the rate-determining step often determines the kinetics. In consecutive first order reactions, a steady state approximation can simplify the rate law. The activation energy for a reaction is experimentally determined through the Arrhenius equation and the Eyring equation. The main factors that influence the reaction rate include: the physical state of the reactants, the concentrations of the reactants, the temperature at which the reaction occurs, and whether or not any catalysts are present in the reaction.

text: Van 't Hoff

text: studied chemical dynamics and published in 1884 his famous "Etudes de dynamique chimique". In 1901 he was awarded by the first Nobel Prize in Chemistry "in recognition of the extraordinary services he has rendered by the discovery of the laws of chemical dynamics and osmotic pressure in solutions". After van 't Hoff, chemical kinetics deals with the experimental determination of

text: reaction rate

text: s from which

text: rate law

text: s and

text: rate constants

text: are derived. Relatively simple

text: rate law

text: s exist for

text: zero order reactions

text: (for which reaction rates are independent of concentration),

text: first order reaction

text: s, and

text: second order reaction

text: s, and can be derived for others.

text: Elementary reaction

text: s follow the

text: law of mass action

text: , but the rate law of

text: stepwise reaction

text: s has to be derived by combining the rate laws of the various elementary steps, and can become rather complex. In consecutive reactions, the

text: rate-determining step

text: often determines the kinetics. In consecutive first order reactions, a

text: steady state

text: approximation can simplify the

text: rate law

text: . The

text: activation energy

text: for a reaction is experimentally determined through the

text: Arrhenius equation

text: and the

text: Eyring equation

text: . The main factors that influence the

text: reaction rate

text: include: the

text: physical state

text: of the reactants, the

text: concentrations

text: of the reactants, the

text: temperature

text: at which the reaction occurs, and whether or not any

text: catalysts

text: are present in the reaction.

text: In its most commonly used form, the Damköhler number relates the reaction timescale to the convection time scale, flow rate, through the reactor for continuous (plug flow or stirred tank) or semibatch chemical processes:

text: In its most commonly used form, the Damköhler number relates the reaction timescale to the

text: convection

text: time scale,

text: flow rate

text: , through the reactor for continuous (

text: plug flow

text: or

text: stirred tank

text: ) or

text: semibatch

text: chemical processes:

text: The reactions are due to collisions of reactant species. The frequency with which the molecules or ions collide depends upon their concentrations. The more crowded the molecules are, the more likely they are to collide and react with one another. Thus, an increase in the concentrations of the reactants will usually result in the corresponding increase in the reaction rate, while a decrease in the concentrations will usually have a reverse effect. For example, combustion will occur more rapidly in pure oxygen than in air (21% oxygen).

text: The reactions are due to collisions of reactant species. The frequency with which the molecules or ions collide depends upon their

text: concentration

text: s. The more crowded the molecules are, the more likely they are to collide and react with one another. Thus, an increase in the concentrations of the reactants will usually result in the corresponding increase in the reaction rate, while a decrease in the concentrations will usually have a reverse effect. For example,

text: combustion

text: will occur more rapidly in pure oxygen than in air (21% oxygen).

text: Two aspects are involved in the initial formulation of the law: 1) the equilibrium aspect, concerning the composition of a reaction mixture at equilibrium and 2) the kinetic aspect concerning the rate equations for elementary reactions. Both aspects stem from the research performed by Cato M. Guldberg and Peter Waage between 1864 and 1879 in which equilibrium constants were derived by using kinetic data and the rate equation which they had proposed. Guldberg and Waage also recognized that chemical equilibrium is a dynamic process in which rates of reaction for the forward and backward reactions must be equal at chemical equilibrium. In order to derive the expression of the equilibrium constant appealing to kinetics, the expression of the rate equation must be used. The expression of the rate equations was rediscovered later independently by Jacobus Henricus van 't Hoff.

text: Two aspects are involved in the initial formulation of the law: 1) the equilibrium aspect, concerning the composition of a

text: reaction

text: mixture at

text: equilibrium

text: and 2) the

text: kinetic

text: aspect concerning the

text: rate equation

text: s for

text: elementary reaction

text: s. Both aspects stem from the research performed by

text: Cato M. Guldberg

text: and

text: Peter Waage

text: between 1864 and 1879 in which equilibrium constants were derived by using kinetic data and the rate equation which they had proposed. Guldberg and Waage also recognized that chemical equilibrium is a dynamic process in which

text: rates of reaction

text: for the forward and backward reactions must be equal at

text: chemical equilibrium

text: . In order to derive the expression of the equilibrium constant appealing to kinetics, the expression of the rate equation must be used. The expression of the rate equations was rediscovered later independently by

text: Jacobus Henricus van 't Hoff

text: In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structure, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light; thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor ethat is the probability of molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation.The activation energy necessary for a chemical reaction can be in the form of thermal energy.

text: In the context of

text: chemistry

text: , energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structure, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light; thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be

text: exergonic

text: if the final state is lower on the energy scale than the initial state; in the case of

text: endergonic

text: reactions the situation is the reverse.

text: Chemical reaction

text: s are invariably not possible unless the reactants surmount an energy barrier known as the

text: activation energy

text: . The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor ethat is the probability of molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the

text: Arrhenius equation

text: .The activation energy necessary for a chemical reaction can be in the form of thermal energy.

text: In 1956 Flanigen began working on molecular sieves. Molecular sieves are crystal compounds with molecular sized pores that can filter or separate very complex substances. Edith Flanigen is best known as the inventor of zeolite Y, a specific molecular sieve. Zeolite Y was a certain type of molecular sieve that could refine petroleum. Zeolite Y surpassed Zeolite X before it. When refining "crude oil", or petroleum, it must be separated into all of its different parts, or fractions. Gasoline is one of the many fractions that come from refining petroleum. Flanigen's zeolites are used as catalysts, or a substance that enhances chemical reactions. Zeolite Y is a catalyst that enhances the amount of gasoline fractioned from petroleum, making refining petroleum safer and more productive.

text: In 1956 Flanigen began working on

text: molecular sieves

text: Molecular sieves

text: are crystal compounds with molecular sized pores that can filter or separate very complex substances. Edith Flanigen is best known as the inventor of

text: zeolite Y

text: , a specific molecular sieve.

text: Zeolite Y

text: was a certain type of molecular sieve that could refine petroleum.

text: Zeolite Y

text: surpassed

text: Zeolite X

text: before it. When refining "

text: crude oil

text: ", or petroleum, it must be separated into all of its different parts, or

text: fractions

text: . Gasoline is one of the many fractions that come from

text: refining petroleum

text: . Flanigen's

text: zeolites

text: are used as

text: catalysts

text: , or a substance that enhances chemical reactions.

text: Zeolite Y

text: is a catalyst that enhances the amount of gasoline fractioned from petroleum, making refining petroleum safer and more productive.

text: A chemical reaction can be defined by two important parameters- the Gibbs free energy associated with a chemical transformation and the rate of such a transformation. These parameters are independent of each other. While free energy change describes the stability of products relative to reactants, the rate of any reaction is defined by the energy of the transition state relative to the starting material. Depending on these parameters, a reaction can be favorable or unfavorable, fast or slow and reversible or irreversible, as shown in figure 8.

text: A chemical reaction can be defined by two important parameters- the

text: Gibbs free energy

text: associated with a chemical transformation and the rate of such a transformation. These parameters are independent of each other. While free energy change describes the stability of products relative to reactants, the rate of any reaction is defined by the energy of the transition state relative to the starting material. Depending on these parameters, a reaction can be favorable or unfavorable, fast or slow and reversible or irreversible, as shown in figure 8.

text: Inner sphere or bonded electron transfer is a redox chemical reaction that proceeds via a covalent linkage—a strong electronic interaction—between the oxidant and the reductant reactants.  In Inner Sphere (IS) electron transfer (ET), a  ligand bridges the two metal redox centers during the electron transfer event.  Inner  sphere reactions are inhibited by large ligands, which prevent the formation of the crucial bridged intermediate. Thus, IS ET is rare in biological systems, where redox sites are often shielded by bulky proteins.  Inner sphere ET is usually used to describe reactions involving transition metal complexes and most of this article is written from this perspective.  However, redox centers can consist of organic groups rather than metal centers.

text: Inner sphere or bonded electron transfer is a

text: redox

text: chemical reaction that proceeds via a

text: covalent

text: linkage—a strong electronic interaction—between the oxidant and the reductant reactants.  In Inner Sphere (IS) electron transfer (ET), a

text: ligand

text: bridges the two metal redox centers during the electron transfer event.  Inner  sphere reactions are inhibited by large ligands, which prevent the formation of the crucial bridged intermediate. Thus, IS ET is rare in biological systems, where redox sites are often shielded by bulky proteins.  Inner sphere ET is usually used to describe reactions involving transition metal complexes and most of this article is written from this perspective.  However, redox centers can consist of organic groups rather than metal centers.

text: A first-order reaction is a reaction that proceeds at a rate that depends linearly on only one reactant concentration.

text: A first-order reaction is a

text: reaction

text: that proceeds at a rate that depends linearly on only one

text: reactant

text: concentration.

text: Reaction wheels are usually implemented as special electric motors, mounted along at least three directions: for example along the x, y and z axes provides no redundancy; while mounting four along tetrahedral axes provides redundancy. Changes in speed  (in either direction) are controlled electronically by computer. The strength of the materials used in a reaction wheel determine the speed at which the wheel would come apart, and therefore how much angular momentum it can store.

text: Reaction wheels are usually implemented as special

text: electric motor

text: s, mounted along at least three directions: for example along the x, y and z axes provides no redundancy; while mounting four along tetrahedral axes provides redundancy. Changes in speed  (in either direction) are controlled electronically by computer. The strength of the materials used in a reaction wheel determine the speed at which the wheel would come apart, and therefore how much

text: angular momentum

text: it can store.

text: Generally speaking,  anything that increases the rate of a process is a "catalyst", a term derived from Greek καταλύειν, meaning "to annul," or "to untie," or "to pick up."  The concept of catalysis was invented by chemist Elizabeth Fulhame and described in a 1794 book, based on her novel work in oxidation-reduction experiments. The term catalysis was later used by Jöns Jakob Berzelius in 1835 to describe reactions that are accelerated by substances that remain unchanged after the reaction. Fulhame, who predated Berzelius, did work with water as opposed to metals in her reduction experiments. Other 18th century chemists who worked in catalysis were Eilhard Mitscherlich who referred to it as contact processes, and Johann Wolfgang Döbereiner who spoke of contact action. He developed Döbereiner's lamp, a lighter based on hydrogen and a platinum sponge, which became a commercial success in the 1820s that lives on today. Humphry Davy discovered the use of platinum in catalysis. In the 1880s, Wilhelm Ostwald at Leipzig University started a systematic investigation into reactions that were catalyzed by the presence of acids and bases, and found that chemical reactions occur at finite rates and that these rates can be used to determine the strengths of acids and bases. For this work, Ostwald was awarded the 1909 Nobel Prize in Chemistry.

text: Generally speaking,  anything that increases the rate of a process is a "catalyst", a term derived from

text: Greek

text: καταλύειν

text: , meaning "to annul," or "to untie," or "to pick up."  The concept of catalysis was invented by chemist

text: Elizabeth Fulhame

text: and described in a 1794 book, based on her novel work in oxidation-reduction experiments. The term catalysis was later used by

text: Jöns Jakob Berzelius

text: in 1835 to describe reactions that are accelerated by substances that remain unchanged after the reaction.

text: Fulhame

text: , who predated Berzelius, did work with water as opposed to metals in her reduction experiments. Other 18th century chemists who worked in catalysis were

text: Eilhard Mitscherlich

text: who referred to it as contact processes, and

text: Johann Wolfgang Döbereiner

text: who spoke of contact action. He developed

text: Döbereiner's lamp

text: , a

text: lighter

text: based on

text: hydrogen

text: and a

text: platinum

text: sponge, which became a commercial success in the 1820s that lives on today.

text: Humphry Davy

text: discovered the use of platinum in catalysis. In the 1880s,

text: Wilhelm Ostwald

text: at

text: Leipzig University

text: started a systematic investigation into reactions that were catalyzed by the presence of

text: acid

text: s and bases, and found that chemical reactions occur at finite rates and that these rates can be used to determine the strengths of acids and bases. For this work, Ostwald was awarded the 1909

text: Nobel Prize in Chemistry

text: is the substrate concentration at which the reaction rate is half of

text: In heterogeneous catalysis, the reactants diffuse to the catalyst surface and adsorb onto it, via the formation of chemical bonds.  After reaction, the products desorb from the surface and diffuse away.  Understanding the transport phenomena and surface chemistry such as dispersion is important.  If diffusion rates are not taken into account, the reaction rates for various reactions on surfaces depend solely on the rate constants and reactant concentrations.For solid heterogeneous catalysts, the surface area of the catalyst is critical since it determines the availability of catalytic sites.  Surface areas can be large, for example some mesoporous silicates have areas of 1000 m/g. The most common approach to maximizing surface area is by the use of catalyst supports, which are the materials over which the catalysts are spread.

text: In heterogeneous catalysis, the reactants

text: diffuse

text: to the catalyst surface and

text: adsorb

text: onto it, via the formation of chemical bonds.  After reaction, the products desorb from the surface and diffuse away.  Understanding the transport phenomena and

text: surface chemistry

text: such as

text: dispersion

text: is important.  If diffusion rates are not taken into account, the reaction rates for various

text: reactions on surfaces

text: depend solely on the rate constants and reactant concentrations.For solid heterogeneous catalysts, the surface area of the catalyst is critical since it determines the availability of catalytic sites.  Surface areas can be large, for example some

text: mesoporous silicates

text: have areas of 1000 m/g. The most common approach to maximizing surface area is by the use of

text: catalyst support

text: s, which are the materials over which the catalysts are spread.

text: Since the reaction timescale is determined by the reaction rate, the exact formula for the Damköhler number varies according to the rate law equation. For a general chemical reaction A → B of nth order, the Damköhler number for a convective flow system is defined as:

text: Since the reaction timescale is determined by the reaction rate, the exact formula for the Damköhler number varies according to the rate law equation. For a general chemical reaction A → B of nth

text: order

text: , the Damköhler number for a convective flow system is defined as:

text: When more than one reactant participates in a reaction, the yield is usually calculated based on the amount of the limiting reactant, whose amount is less than stoichiometrically equivalent (or just equivalent) to the amounts of all other reactants present. Other reagents present in amounts greater than required to react with all the limiting reagent present are considered excess. As a result, the yield should not be automatically taken as a measure for reaction efficiency.

text: When more than one reactant participates in a reaction, the yield is usually calculated based on the amount of the

text: limiting reactant

text: , whose amount is less than

text: stoichiometrically

text: equivalent (or just equivalent) to the amounts of all other reactants present. Other reagents present in amounts greater than required to react with all the limiting reagent present are considered excess. As a result, the yield should not be automatically taken as a measure for reaction efficiency.

text: The most commonly encountered form of chemisorption in industry, occurs when a solid catalyst interacts with a gaseous feedstock, the reactant/s.  The adsorption of reactant/s to the catalyst surface creates a chemical bond, altering the electron density around the reactant molecule and allowing it to undergo reactions that would not normally be available to it.

text: The most commonly encountered form of chemisorption in industry, occurs when a solid

text: catalyst

text: interacts with a gaseous feedstock, the reactant/s.  The adsorption of reactant/s to the catalyst surface creates a chemical bond, altering the electron density around the reactant molecule and allowing it to undergo reactions that would not normally be available to it.

text: Lavoisier's researches included some of the first truly quantitative chemical experiments. He carefully weighed the reactants and products of a chemical reaction in a sealed glass vessel so that no gases could escape, which was a crucial step in the advancement of chemistry. In 1774, he showed that, although matter can change its state in a chemical reaction, the total mass of matter is the same at the end as at the beginning of every chemical change. Thus, for instance, if a piece of wood is burned to ashes, the total mass remains unchanged if gaseous reactants and products are included. Lavoisier's experiments supported the law of conservation of mass. In France it is taught as Lavoisier's Law and is paraphrased from a statement in his "Traité Élémentaire de Chimie" to "Rien ne se perd, rien ne se crée, tout se transforme." ("Nothing is lost, nothing is created, everything is transformed."). Mikhail Lomonosov (1711–1765) had previously expressed similar ideas in 1748 and proved them in experiments; others whose ideas pre-date the work of Lavoisier include Jean Rey (1583–1645), Joseph Black (1728–1799), and Henry Cavendish (1731–1810). (See An Historical Note on the Conservation of Mass)

text: Lavoisier's researches included some of the first truly

text: quantitative chemical experiments

text: . He carefully weighed the reactants and products of a chemical reaction in a sealed glass vessel so that no

text: gas

text: es could escape, which was a crucial step in the advancement of chemistry. In 1774, he showed that, although matter can change its state in a chemical reaction, the total mass of matter is the same at the end as at the beginning of every chemical change. Thus, for instance, if a piece of wood is burned to ashes, the total mass remains unchanged if gaseous reactants and products are included. Lavoisier's experiments supported the law of

text: conservation of mass

text: . In France it is taught as Lavoisier's Law and is paraphrased from a statement in his "

text: Traité Élémentaire de Chimie

text: " to "Rien ne se perd, rien ne se crée, tout se transforme." ("Nothing is lost, nothing is created, everything is transformed.").

text: Mikhail Lomonosov

text: (1711–1765) had previously expressed similar ideas in 1748 and proved them in experiments; others whose ideas pre-date the work of Lavoisier include

text: Jean Rey

text: Joseph Black

text: (1728–1799), and

text: Henry Cavendish

text: (1731–1810). (See An Historical Note on the Conservation of Mass)

text: Yup tutors are familiar with, and can thoroughly explain, every math concept covered by the Common Core up to AP Calculus Level AB including questions in Algebra, Basic Calculus, Geometry, Pre-algebra, and Trigonometry. Yup also offers support in Physics up to the AP Physics level 1 and 2 specifically: Kinematics, Force and Mechanics, Gravitation and Circular Motion, Work, Energy and Momentum, Torque and Rotational Mechanics, Fluid Mechanics, Thermodynamics and Kinetic Theory, Waves and Optics, and Electromagnetism. Additionally, Yup tutors can help students with Chemistry up to AP Chemistry. These topics include: Structure of Matter, Bonding and Intermolecular Forces, Chemical Reactions and Stoichiometry, Kinetics and Reaction Rates, and Chemical Equilibrium.  Additionally, Yup offers homework resources on its website. These resources offer definitions of important topics, sample problems and explanations and videos.

text: Yup tutors are familiar with, and can thoroughly explain, every math concept covered by the Common Core up to AP Calculus Level AB including questions in

text: Algebra

text: , Basic

text: Calculus

text: Geometry

text: Pre-algebra

text: , and

text: Trigonometry

text: . Yup also offers support in Physics up to the

text: AP Physics level 1

text: and

text: specifically:

text: Kinematics

text: , Force and Mechanics,

text: Gravitation

text: and

text: Circular Motion

text: , Work, Energy and Momentum, Torque and Rotational Mechanics,

text: Fluid Mechanics

text: Thermodynamics

text: and

text: Kinetic Theory

text: , Waves and Optics, and

text: Electromagnetism

text: . Additionally, Yup tutors can help students with Chemistry up to

text: AP Chemistry

text: . These topics include: Structure of Matter, Bonding and

text: Intermolecular Forces

text: Chemical Reactions

text: and

text: Stoichiometry

text: , Kinetics and Reaction Rates, and

text: Chemical Equilibrium.

text: Additionally, Yup offers homework resources on its website. These resources offer definitions of important topics, sample problems and explanations and videos.

text: The reaction of MDI and polyol takes place at higher temperatures compared with the reaction temperature for the manufacture of PUR. At these elevated temperatures and in the presence of specific catalysts, MDI will first react with itself, producing a stiff, ring molecule, which is a reactive intermediate (a tri-isocyanate isocyanurate compound). Remaining MDI and the tri-isocyanate react with polyol to form a complex poly(urethane-isocyanurate) polymer (hence the use of the abbreviation PUI as an alternative to PIR), which is foamed in the presence of a suitable blowing agent. This isocyanurate polymer has a relatively strong molecular structure, because of the combination of strong chemical bonds, the ring structure of isocyanurate and high cross link density, each contributing to the greater stiffness than found in comparable polyurethanes. The greater bond strength also means these are more difficult to break, and as a result a PIR foam is chemically and thermally more stable: breakdown of isocyanurate bonds is reported to start above 200°C, compared with urethane at 100 to 110°C.

text: The reaction of MDI and polyol takes place at higher temperatures compared with the reaction temperature for the manufacture of PUR. At these elevated temperatures and in the presence of specific catalysts, MDI will first react with itself, producing a stiff, ring molecule, which is a reactive intermediate (a tri-isocyanate isocyanurate compound). Remaining MDI and the tri-isocyanate react with polyol to form a complex poly(urethane-isocyanurate) polymer (hence the use of the abbreviation PUI as an alternative to PIR), which is foamed in the presence of a suitable blowing agent. This

text: isocyanurate

text: polymer has a relatively strong molecular structure, because of the combination of strong chemical bonds, the ring structure of isocyanurate and high cross link density, each contributing to the greater stiffness than found in comparable polyurethanes. The greater bond strength also means these are more difficult to break, and as a result a PIR foam is chemically and thermally more stable: breakdown of isocyanurate bonds is reported to start above 200°C, compared with urethane at 100 to 110°C.

text: If the same hydrolysis reaction is catalyzed by imidazole, the rate equation becomes r = k[imidazole][CHCOOCH]. The rate is first-order in one reactant (ethyl acetate), and also first-order in imidazole which as a catalyst does not appear in the overall chemical equation.

text: If the same hydrolysis reaction is

text: catalyzed

text: by

text: imidazole

text: , the rate equation becomes r = k[imidazole][CHCOOCH]. The rate is first-order in one reactant (ethyl acetate), and also first-order in imidazole which as a catalyst does not appear in the overall chemical equation.

text: For the subsequent reaction at high temperatures, it is necessary to choose a suitable container material which is chemically inert to the reactants under the heating conditions used. The noble metals, platinum and gold, are usually suitable. Containers may be crucibles or boats made from foil. For low temperature reactions, other metals like Nickel (below 600–700C) can be used.

text: For the subsequent reaction at high temperatures, it is necessary to choose a suitable container material which is

text: chemically inert

text: to the

text: reactant

text: s under the heating conditions used. The

text: noble metals

text: platinum

text: and

text: gold

text: , are usually suitable. Containers may be

text: crucible

text: s or boats made from foil. For low temperature reactions, other metals like

text: Nickel

text: (below 600–700C) can be used.

text: Chemical King is a mutant with the power to act as a human catalyst.  He can speed up or slow down any chemical reaction; for example, he can cause iron to rapidly rust, or even burst into flames from rapid oxidation.  His powers can affect the chemical reactions in the human body, rendering an opponent unconscious from shock, but take several seconds and can only focus on a single opponent at a time. Late in his career, Chemical King displayed the ability to change energy reaction rates as well, causing batteries to drain of power and force fields to decay. As the final act before his death, he used his powers to alter and absorb vast amounts of radiation capable of paralyzing Superboy.

text: Chemical King is a mutant with the power to act as a human catalyst.  He can speed up or slow down any chemical reaction; for example, he can cause iron to rapidly rust, or even burst into flames from rapid oxidation.  His powers can affect the chemical reactions in the human body, rendering an opponent unconscious from shock, but take several seconds and can only focus on a single opponent at a time. Late in his career, Chemical King displayed the ability to change energy reaction rates as well, causing batteries to drain of power and force fields to decay. As the final act before his death, he used his powers to alter and absorb vast amounts of radiation capable of paralyzing

text: Superboy

text: The surface area is typically determined via a BET measurement using a gas that will be preferentially adsorbed on metallic surfaces, such as hydrogen. Using this type of measurement, almost all the exposed area in a particle of the catalyst has been shown to have Ni on its surface. Since Ni is the active metal of the catalyst, a large Ni surface area implies a large surface is available for reactions to occur simultaneously, which is reflected in an increased catalyst activity. Commercially available Raney nickel has an average Ni surface area of 100 m per gram of catalyst.

text: The surface area is typically determined via a BET measurement using a gas that will be preferentially adsorbed on metallic surfaces, such as

text: hydrogen

text: . Using this type of measurement, almost all the exposed area in a particle of the catalyst has been shown to have Ni on its surface. Since Ni is the active metal of the catalyst, a large Ni surface area implies a large surface is available for reactions to occur simultaneously, which is reflected in an increased catalyst activity. Commercially available Raney nickel has an average Ni surface area of 100 m per gram of catalyst.

text: The speed at which reactions takes place is studied by reaction kinetics. The rate depends on various parameters, such as:

text: The speed at which reactions takes place is studied by

text: reaction kinetics

text: . The rate depends on various parameters, such as:

text: Temperature usually has a major effect on the rate of a chemical reaction. Molecules at a higher temperature have more thermal energy. Although collision frequency is greater at higher temperatures, this alone contributes only a very small proportion to the increase in rate of reaction. Much more important is the fact that the proportion of reactant molecules with sufficient energy to react (energy greater than activation energy: E > E) is significantly higher and is explained in detail by the Maxwell–Boltzmann distribution of molecular energies.

text: Temperature

text: usually has a major effect on the rate of a chemical reaction. Molecules at a higher temperature have more

text: thermal energy

text: . Although collision frequency is greater at higher temperatures, this alone contributes only a very small proportion to the increase in rate of reaction. Much more important is the fact that the proportion of reactant molecules with sufficient energy to react (energy greater than

text: activation energy

text: : E > E) is significantly higher and is explained in detail by the

text: Maxwell–Boltzmann distribution

text: of molecular energies.

text: Oliver Sava of The A.V. Club gave the season a B+ rating. He described Raj as the "weak link of the show" as he has not "[evolved] like the rest of the cast" and is "trapped in season one mode". Sava gave high ratings to episodes where Raj did not feature prominently, such as "The Pulled Groin Extrapolation" or "The Russian Rocket Reaction" and described "The Wiggly Finger Catalyst" (an episode focusing on Raj) as "one of the series' worst", giving it a D+ rating. Sava's favorite relationship on the series is between Amy and Penny.

text: Oliver Sava of

text: The A.V. Club

text: gave the season a B+ rating. He described Raj as the "weak link of the show" as he has not "[evolved] like the rest of the cast" and is "trapped in season one mode". Sava gave high ratings to episodes where Raj did not feature prominently, such as "

text: The Pulled Groin Extrapolation

text: " or "

text: The Russian Rocket Reaction

text: " and described "

text: The Wiggly Finger Catalyst

text: " (an episode focusing on Raj) as "one of the series' worst", giving it a D+ rating. Sava's favorite relationship on the series is between Amy and Penny.

text: Cycloadditions with reactants that are liquids at room temperature are best performed by simply mixing the two reactants without solvent. If one of the reactants is gaseous, it is more convenient to use a solvent. Although polar solvents and catalysts accelerate the cycloaddition, they are not of general utility since they also accelerate dimerization. The progress of the reaction can be estimated by disappearance of the characteristic yellow color of the ketene, by loss of the band at about 2100 cm in the infrared spectrum, or by H NMR spectroscopy. Ketene, monoalkylketenes, and dimethylketene are usually allowed to react at or below room temperature, whereas the higher molecular weight ketenes can be heated to temperatures above 100°. The ketene is usually used in excess when dimerization is a major side reaction. The success of the reaction is often determined by the relative rates of cycloaddition and dimerization of the ketene.

text: Chemical ionization was developed in the 1960s. Ionization of sample (analyte) is achieved by interaction of its molecules with reagent ions. The analyte is ionized by ion-molecule reactions during collisions in the source. The process may involve transfer of an electron, a proton or other charged species between the reactants. This is a less energetic procedure than electron ionization and the ions produced are, for example, protonated molecules:  [M + H]. These ions are often relatively stable, tending not to fragment as readily as ions produced by electron ionization.

text: Chemical ionization was developed in the 1960s. Ionization of sample (analyte) is achieved by interaction of its molecules with reagent ions. The analyte is ionized by ion-molecule reactions during collisions in the source. The process may involve transfer of an electron, a proton or other charged species between the reactants. This is a less energetic procedure than

text: electron ionization

text: and the ions produced are, for example, protonated molecules:  [M + H]. These ions are often relatively stable, tending not to fragment as readily as ions produced by

text: electron ionization

text: Chemical oxidation is one half of a redox reaction, which results in the loss of electrons. One of the reactants in the reaction becomes oxidized, or loses electrons, while the other reactant becomes reduced, or gains electrons. In ISCO, oxidizing compounds, compounds that give electrons away to other compounds in a reaction, are used to change the contaminants into harmless compounds. The in situ in ISCO is just Latin for "in place", signifying that ISCO is a chemical oxidation reaction that occurs at the site of the contamination.

text: Chemical oxidation is one half of a

text: redox

text: reaction, which results in the loss of electrons. One of the reactants in the reaction becomes oxidized, or loses electrons, while the other reactant becomes reduced, or gains electrons. In ISCO, oxidizing compounds, compounds that give electrons away to other compounds in a reaction, are used to change the contaminants into harmless compounds. The

text: in situ

text: in ISCO is just Latin for "in place", signifying that ISCO is a chemical oxidation reaction that occurs at the site of the contamination.

text: A lo-fi music video for the song, shot on VHS, was helmed by German feature director Wolfgang Becker and cinematographed by Jürgen Jürges. It was released onto YouTube on 20 March 2013. Nick Knight of Promo News wrote: "It’s a wonderfully absurd comedy exploring a dynamic of crumbling love and trust between the members of Travis, the catalyst being the presence of another guy who happens to be played with a certain level of menace by the director himself."

text: A lo-fi music video for the song, shot on

text: VHS

text: , was helmed by German feature director

text: Wolfgang Becker

text: and cinematographed by

text: Jürgen Jürges

text: . It was released onto

text: YouTube

text: on 20 March 2013. Nick Knight of Promo News wrote: "It’s a wonderfully absurd comedy exploring a dynamic of crumbling love and trust between the members of Travis, the catalyst being the presence of another guy who happens to be played with a certain level of menace by the director himself."

text: A number of common processes fractionate hydrogen isotopes to produce the isotope variations found in nature. Common physical processes include precipitation and evaporation.  Chemical reactions also have the potential to heavily influence the partitioning of heavy and light isotopes between pools. The rate of a chemical reaction depends in part on the energies of the chemical bonds being formed and broken in the reaction. Since different isotopes have different masses, the bond energies are different between different isotopologues of a chemical species. This will result in a difference in the rate of a reaction for the different isotopologues, resulting in a fractionation of the different isotopes between the reactant and product in a chemical reaction. This is known as the kinetic isotope effect. A classic example of such an isotope effect is the D/H ratio difference in the equilibrium between HO and H which can have an alpha value of as much as 3-4.

text: A number of common processes fractionate hydrogen isotopes to produce the isotope variations found in nature. Common physical processes include precipitation and evaporation.  Chemical reactions also have the potential to heavily influence the partitioning of heavy and light isotopes between pools. The rate of a chemical reaction depends in part on the energies of the chemical bonds being formed and broken in the reaction. Since different isotopes have different masses, the bond energies are different between different

text: isotopologues

text: of a chemical species. This will result in a difference in the rate of a reaction for the different isotopologues, resulting in a fractionation of the different isotopes between the reactant and product in a chemical reaction. This is known as the kinetic isotope effect. A classic example of such an isotope effect is the D/H ratio difference in the equilibrium between HO and H which can have an alpha value of as much as 3-4.

text: Decomposition of reagents isbimolecular (second-order reaction rate), so low amounts of oxone and catalyst are used.

text: Decomposition of reagents isbimolecular (

text: second-order reaction

text: rate), so low amounts of oxone and catalyst are used.

text: Silica aerogels are typically synthesized by using a sol-gel process. The first step is the creation of a colloidal suspension of solid particles known as a "sol". The precursors are a liquid alcohol such as ethanol which is mixed with a silicon alkoxide, such as tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), and polyethoxydisiloxane (PEDS) (earlier work used sodium silicates). The solution of silica is mixed with a catalyst and allowed to gel during a hydrolysis reaction which forms particles of silicon dioxide. The oxide suspension begins to undergo condensation reactions which result in the creation of metal oxide bridges (either M–O–M, "oxo" bridges or M–OH–M, "ol" bridges) linking the dispersed colloidal particles.  These reactions generally have moderately slow reaction rates, and as a result either acidic or basic catalysts are used to improve the processing speed. Basic catalysts tend to produce more transparent aerogels and minimize the shrinkage during the drying process and also strengthen it to prevent pore collapse during drying.

text: Silica aerogels are typically synthesized by using a sol-gel process. The first step is the creation of a

text: colloidal

text: suspension

text: of solid particles known as a "sol". The precursors are a liquid

text: alcohol

text: such as ethanol which is mixed with a silicon

text: alkoxide

text: , such as tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), and polyethoxydisiloxane (PEDS) (earlier work used sodium silicates). The solution of silica is mixed with a catalyst and allowed to gel during a

text: hydrolysis

text: reaction which forms particles of silicon dioxide. The oxide suspension begins to undergo

text: condensation reaction

text: s which result in the creation of metal oxide bridges (either

text: M–O–M, "oxo" bridges

text: or M–OH–M, "

text: ol

text: " bridges) linking the dispersed colloidal particles.  These reactions generally have moderately slow reaction rates, and as a result either acidic or basic

text: catalyst

text: s are used to improve the processing speed. Basic catalysts tend to produce more transparent aerogels and minimize the shrinkage during the drying process and also strengthen it to prevent pore collapse during drying.

text: Organic reactions are chemical reactions involving organic compounds.   The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions and redox reactions. In organic synthesis, organic reactions are used in the construction of new organic molecules. The production of many man-made chemicals such as drugs, plastics, food additives, fabrics depend on organic reactions.

text: Organic reactions are

text: chemical reaction

text: s involving

text: organic compound

text: s.   The basic

text: organic chemistry

text: reaction types are

text: addition reaction

text: s,

text: elimination reaction

text: s,

text: substitution reaction

text: s,

text: pericyclic reaction

text: s,

text: rearrangement reaction

text: s,

text: photochemical reactions

text: and

text: redox reactions

text: . In

text: organic synthesis

text: , organic reactions are used in the construction of new organic molecules. The production of many man-made chemicals such as drugs, plastics, food additives, fabrics depend on organic reactions.

text: Hoffmann first proposed a mechanism for the MBH reaction. The first reaction step involves 1,4-addition of the catalytic tertiary amine to the activated alkene to generate the zwitterionic aza-enolate. In the second step, this enolate adds to an aldehyde via an aldol addition. The third step involves intramolecular proton shift, which subsequently generates the final MBH adduct and releases the catalyst via E2 or E1cb elimination in the last step. Hill and Isaacs performed kinetic experiments to probe the mechanistic details. The rate of reaction between acrylonitrile and acetaldehyde was first order in concentrations of acrylonitrile, acetaldehyde, and DABCO. Hill and Isaacs proposed that the aldol addition step, which involves all three reactants, thus is the rate determining step. That they did not observe kinetic isotope effect using α-deutrated acrylonitrile also supported this statement.

text: Cyclisation carried out with a diyne and a separate alkyne affords greater control as well as high atom economy.  Using commercially available cyclopentadienylcobalt dicarbonyl, CpCo(CO), as catalyst, bis(trimethylsilyl)acetylene (BTMSA) will react with a diyne-1,2-disubstituted benzene to form an anthroquinone aromatic system as shown below:  Benzyne, generated in situ from a bezene ring bearing ortho-distributed triflate and trimethylsilyl substituents, can be used to generate an aryne in place of an acetylene and combined with a suitable diyne. Such a benzene derivative reacts with 1,7-octadiyne in the presence of a suitable catalyst to generate a naphthalene system.  This is an example of a hexadehydro Diels-Alder reaction.

text: Cyclisation carried out with a

text: diyne

text: and a separate alkyne affords greater control as well as high

text: atom economy

text: .  Using commercially available

text: cyclopentadienylcobalt dicarbonyl

text: , CpCo(CO), as catalyst,

text: bis(trimethylsilyl)acetylene

text: (BTMSA) will react with a diyne-1,2-disubstituted benzene to form an

text: anthroquinone

text: aromatic system as shown below:

text: Benzyne

text: , generated in situ from a bezene ring bearing

text: ortho

text: -distributed

text: triflate

text: and

text: trimethylsilyl

text: substituents, can be used to generate an

text: aryne

text: in place of an acetylene and combined with a suitable diyne. Such a benzene derivative reacts with 1,7-octadiyne in the presence of a suitable catalyst to generate a naphthalene system.  This is an example of a

text: hexadehydro Diels-Alder reaction

text: The transition metals and their compounds are known for their homogeneous and heterogeneous catalytic activity. This activity is ascribed to their ability to adopt multiple oxidation states and to form complexes. Vanadium(V) oxide (in the contact process), finely divided iron (in the Haber process), and nickel (in catalytic hydrogenation) are some of the examples. Catalysts at a solid surface (nanomaterial-based catalysts) involve the formation of bonds between reactant molecules and atoms of the surface of the catalyst (first row transition metals utilize 3d and 4s electrons for bonding). This has the effect of increasing the concentration of the reactants at the catalyst surface and also weakening of the bonds in the reacting molecules (the activation energy is lowered). Also because the transition metal ions can change their oxidation states, they become more effective as catalysts.

text: The transition metals and their compounds are known for their homogeneous and heterogeneous

text: catalytic

text: activity. This activity is ascribed to their ability to adopt multiple oxidation states and to form complexes.

text: Vanadium

text: (V) oxide (in the

text: contact process

text: ), finely divided

text: iron

text: (in the

text: Haber process

text: ), and

text: nickel

text: (in

text: catalytic hydrogenation

text: ) are some of the examples. Catalysts at a solid surface (

text: nanomaterial-based catalyst

text: s) involve the formation of bonds between reactant molecules and atoms of the surface of the catalyst (first row transition metals utilize 3d and 4s electrons for bonding). This has the effect of increasing the concentration of the reactants at the catalyst surface and also weakening of the bonds in the reacting molecules (the activation energy is lowered). Also because the transition metal ions can change their oxidation states, they become more effective as

text: catalysts

text: A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction. The detailed steps of a reaction are not observable in most cases. The conjectured mechanism is chosen because it is thermodynamically  feasible, and has experimental support in isolated intermediates (see next section) or other quantitative and qualitative characteristics of the reaction. It also describes each reactive intermediate, activated complex, and transition state, and which bonds are broken (and in what order), and which bonds are formed (and in what order). A complete mechanism must also explain the reason for the reactants and catalyst used, the stereochemistry observed in reactants and products, all products formed and the amount of each.

text: A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction. The detailed steps of a reaction are not observable in most cases. The conjectured mechanism is chosen because it is thermodynamically  feasible, and has experimental support in isolated intermediates (see next section) or other quantitative and qualitative characteristics of the reaction. It also describes each

text: reactive intermediate

text: activated complex

text: , and

text: transition state

text: , and which bonds are broken (and in what order), and which bonds are formed (and in what order). A complete mechanism must also explain the reason for the

text: reactant

text: s and

text: catalyst

text: used, the

text: stereochemistry

text: observed in reactants and products, all

text: product

text: s formed and the amount of each.

text: Initially, iodide is low and process B generates free iodine, which gradually accumulates. Meanwhile, process A slowly generates the intermediate iodide ion out of the free iodine at an increasing rate proportional to its (i.e. I) concentration. At a certain point, this overwhelms process B, stopping the production of more free iodine, which is still being consumed by process A. Thus, eventually the concentration of free iodine (and thus iodide) falls low enough for process B to start up again and the cycle repeats as long as the original reactants hold out.

text: This model is used when turbulent mixing of the constituents has to be taken into consideration. The k/Ɛ turbulent time scale is used to calculate the reaction rate. A comparison between the turbulent dissipation rates of the fuel, oxidant and products is done and the minimum amongst all is taken as the rate of the reaction. The transport equations for the mass fractions of the constituents are solved using this rate of reaction. Apart from this a mean enthalpy equation is also solved and temperature, density and viscosity are calculated accordingly. The model can also be implemented when finite rate kinetically controlled reaction is to be simulated. In such situation while deciding the rate of the reaction the Arrhenius kinetic rate expression is also taken into account and the rate of reaction is taken as minimum amongst the turbulent dissipation rates of all the constituents and the Arrhenius kinetic rate expression. Since turbulent mixing governs the characteristics of this model, there exists a limit to the quality of the combustion simulation depending upon the type of the turbulent model implemented to represent the flow. The model can also be modified to account for mixing of fine structures during the turbulent reaction. This modification of the model results in the eddy dissipation model which consider the mass fraction of fine structures in its calculations.

text: This model is used when

text: turbulent mixing

text: The SPMD can be deployed in areas with low rates of flow or even in deep water areas. To ensure the safety and correct deployment of the SPMD within deep areas, it is important to attach the device to an anchor as well as a flotation device. To retrieve SPMDs from the field, a boat or a diver may be required, depending on the depth of the canister. An SPMD can concentrate chemicals from the water as well as the sediments in the water column, therefore it is important to know the composition of the sediment and benthic surface before deployment. To reduce interference from chemicals of unwanted sources, anchoring the SPMD at certain depths (e.g. higher for muddy sediments in aquatic systems) can be very beneficial.

text: In specific acid catalysis, protonated solvent is the catalyst.  The reaction rate is proportional to the concentration of the protonated solvent molecules SH. The acid catalyst itself (AH) only contributes to the rate acceleration by shifting the chemical equilibrium between solvent S and AH in favor of the SH species.  This kind of catalysis is common for strong acids in polar solvents, such as water.

text: In specific acid catalysis, protonated solvent is the catalyst.  The

text: reaction rate

text: is proportional to the

text: concentration

text: of the protonated solvent molecules SH. The acid catalyst itself (AH) only contributes to the rate acceleration by shifting the

text: chemical equilibrium

text: between solvent S and AH in favor of the SH species.  This kind of catalysis is common for strong acids in polar solvents, such as water.

text: In aquatic sediments, a number of reactions can transform the chemicals released by the creosote preservatives into more dangerous chemicals. Most creosote preservative compounds have hazards associated with them before they are transformed. Cresol (m-,p-, and o-), phenol, guaiacol, and xylenol (1,3,4- and 1,3,5-) all are acute aquatic hazards prior to going through chemical reactions with the sediments. Alkylation reactions allows for the compounds to transition into more toxic compounds with the addition of R-groups to the major compounds found in creosote preservatives. Compounds formed through alkylation include: 3,4-dimethylphenol, 2,3-dimethylphenol, and 2,5-dimethylphenol, which are all listed as acute environmental hazards.  Biodegradation controls the rate at which the sediment holds the chemicals, and the amount of reactions that are able to take place. The biodegradation process can take place under many different conditions, and vary depending on the compounds that are released. Oxidation-reduction reactions allow for the compounds to be broken down into new forms of more toxic molecules. Studies have shown oxidation-reduction reactions of creosote preservative compounds included compounds that are listed as environmental hazards, such as p-benzoquinone in the oxidation of phenol. Not only are the initial compounds in creosote hazardous to the environment, but the byproducts of the chemical reactions are environmental hazardous as well.

text: In aquatic sediments, a number of reactions can transform the chemicals released by the creosote preservatives into more dangerous chemicals. Most creosote preservative compounds have hazards associated with them before they are transformed.

text: Cresol

text: (m-,p-, and o-),

text: phenol

text: guaiacol

text: , and

text: xylenol

text: Which reactions do occur and how fast is the subject of chemical kinetics, another branch of physical chemistry. A key idea in chemical kinetics is that for reactants to react and form products, most chemical species must go through transition states which are higher in energy than either the reactants or the products and serve as a barrier to reaction. In general, the higher the barrier, the slower the reaction. A second is that most chemical reactions occur as a sequence of elementary reactions, each with its own transition state. Key questions in kinetics include how the rate of reaction depends on temperature and on the concentrations of reactants and catalysts in the reaction mixture, as well as how catalysts and reaction conditions can be engineered to optimize the reaction rate.

text: Which reactions do occur and how fast is the subject of

text: chemical kinetics

text: , another branch of physical chemistry. A key idea in chemical kinetics is that for

text: reactants

text: to react and form

text: products

text: , most chemical species must go through

text: transition state

text: s which are higher in

text: energy

text: than either the reactants or the products and serve as a barrier to reaction. In general, the higher the barrier, the slower the reaction. A second is that most chemical reactions occur as a sequence of

text: elementary reaction

text: s, each with its own transition state. Key questions in kinetics include how the rate of reaction depends on temperature and on the concentrations of reactants and

text: catalysts

text: in the reaction mixture, as well as how catalysts and reaction conditions can be engineered to optimize the reaction rate.

text: Bis(trifluoromethyl)peroxide was first created in trace elements by an electrolysis reaction using aqueous solutions containing trifluoroacetate ion. This was one of the byproducts Frédéric Swarts got when performing trifluoromethylation reactions.[1] Later it was discovered that Bis(trifluoromethyl)peroxide had some unusual properties. This began a search for a more economical production of Bis(trifluoromethyl)peroxide. This was at first done by Porter and Cady. This reaction had a conversion rate of around  20-30% at normal pressure. They increased the conversion using an autoclave. This increased the yield to around 90% which helped procuring the chemical.

text: Energy that can be released (or absorbed) because of a reaction between a set of chemical substances is equal to the difference between the energy content of the products and the reactants, if the initial and final temperatures are the same. This change in energy can be estimated from the bond energies of the various chemical bonds in the reactants and products. It can also be calculated from

text: Energy that can be released (or absorbed) because of a reaction between a set of chemical substances is equal to the difference between the energy content of the products and the reactants, if the initial and final temperatures are the same. This change in energy can be estimated from the

text: bond energies

text: of the various chemical bonds in the reactants and products. It can also be calculated from

text: One of the earliest papers on the NH molecule was in 1976 by Richard M. Crutcher and William D. Watson. They were still trying to pinpoint the absorption line for NH. There was already an already theoretical upper limit of 0.3mÅ (30 fm), but they needed a more exact figure. They thought that NH should normally be produced on grains (directly or indirectly) at about the same rate per atom as OH (hydroxyl) and possibly CH (methine). However, its formation by gas phase reactions was extremely slow and could be neglected in comparison with the possible rate for surface reactions. The presence or absence of NH at a certain abundance level could then be interpreted as evidence concerning the importance of surface reactions. Their hope was to find the abundance ratio between NH and OH. They were unable to find the absorption line for NH. Therefore, the observations were inconclusive.

text: One of the earliest papers on the NH molecule was in 1976 by Richard M. Crutcher and William D. Watson. They were still trying to pinpoint the

text: absorption line

text: for NH. There was already an already theoretical upper limit of 0.3mÅ (30

text: fm

text: ), but they needed a more exact figure. They thought that NH should normally be produced on grains (directly or indirectly) at about the same rate per atom as OH (

text: hydroxyl

text: ) and possibly CH (

text: methine

text: ). However, its formation by gas phase reactions was extremely slow and could be neglected in comparison with the possible rate for surface reactions. The presence or absence of NH at a certain abundance level could then be interpreted as evidence concerning the importance of surface reactions. Their hope was to find the abundance ratio between NH and OH. They were unable to find the absorption line for NH. Therefore, the observations were inconclusive.

text: When the reactants are dissolved in a medium of high ionic strength the quotient of activity coefficients may be taken to be constant. In that case the concentration quotient, K,

text: When the reactants are

text: dissolved

text: in a medium of high

text: ionic strength

text: the quotient of

text: activity coefficient

text: s may be taken to be constant. In that case the concentration quotient, K,

text: Imiquimod is a topical immune-enhancing agent licensed for the treatment of genital warts. Imiquimod stimulates the immune system through the release and up-regulation of cytokines. Treatment with Imiquimod cream applied 2–3 times per week for 12 to 16 weeks was found to result in complete resolution of AKs in 50% of people, compared to 5% of controls. The Imiquimod 3.75% cream has been validated in a treatment regimen consisting of daily application to entire face and scalp for two 2-week treatment cycles, with a complete clearance rate of 36%. While the clearance rate observed with the Imiquimod 3.75% cream was lower than that observed with the 5% cream (36 and 50 percent, respectively), there are lower reported rates of adverse reactions with the 3.75% cream: 19% of individuals using Imiquimod 3.75% cream reported adverse reactions including local erythema, scabbing, and flaking at the application site, while nearly a third of individuals using the 5% cream reported the same types of reactions with Imiquimod treatment. However, it is ultimately difficult to compare the efficacy of the different strength creams directly, as current study data varies in methodology (e.g. duration and frequency of treatment, and amount of skin surface area covered).

text: Imiquimod

text: is a topical immune-enhancing agent licensed for the treatment of genital warts. Imiquimod stimulates the

text: immune system

text: through the release and up-regulation of

text: cytokines

text: . Treatment with Imiquimod cream applied 2–3 times per week for 12 to 16 weeks was found to result in complete resolution of AKs in 50% of people, compared to 5% of controls. The Imiquimod 3.75% cream has been validated in a treatment regimen consisting of daily application to entire face and scalp for two 2-week treatment cycles, with a complete clearance rate of 36%. While the clearance rate observed with the Imiquimod 3.75% cream was lower than that observed with the 5% cream (36 and 50 percent, respectively), there are lower reported rates of adverse reactions with the 3.75% cream: 19% of individuals using Imiquimod 3.75% cream reported adverse reactions including local erythema, scabbing, and flaking at the application site, while nearly a third of individuals using the 5% cream reported the same types of reactions with Imiquimod treatment. However, it is ultimately difficult to compare the efficacy of the different strength creams directly, as current study data varies in methodology (e.g. duration and frequency of treatment, and amount of skin surface area covered).

text: One key difference between the intercepting reaction and the parent reaction described above is the presence of some amount of product in the parent reaction at the interception point. Product inhibition has long been known to influence catalyst efficiency of many systems, and in the case of same-excess experiments, it prevents the intercepting and parent reactions from overlaying. While same-excess experiments as described above cannot attribute catalyst deactivation to any particular cause, product inhibition can be probed by further experiments in which some initial amount of product is added to the intercepting reaction (designed to mimic the amount of product expected to be present in the parent reaction at the same substrate concentration.) A perfect overlay of the rate vs. substrate concentration plots under same-excess-same product conditions indicates that product inhibition does occur under the reaction conditions used. While the failure of the rate vs. substrate concentration plots to overlay under same-excess-same product conditions does not preclude product inhibition, it does, at least, indicate that other catalyst deactivation paths must also be active.

text: At first sight this looks like an exponential multiplied by a factor that is linear in temperature. However, one must remember that free energy is itself a temperature dependent quantity. The free energy of activation is the difference of an enthalpy term and an entropy term multiplied by the absolute temperature. When all of the details are worked out one ends up with an expression that again takes the form of an Arrhenius exponential multiplied by a slowly varying function of T. The precise form of the temperature dependence depends upon the reaction, and can be calculated using formulas from statistical mechanics involving the partition functions of the reactants and of the activated complex.

text: At first sight this looks like an exponential multiplied by a factor that is linear in temperature. However, one must remember that free energy is itself a temperature dependent quantity. The free energy of activation is the difference of an enthalpy term and an entropy term multiplied by the absolute temperature. When all of the details are worked out one ends up with an expression that again takes the form of an Arrhenius exponential multiplied by a slowly varying function of T. The precise form of the temperature dependence depends upon the reaction, and can be calculated using formulas from

text: statistical mechanics

text: involving the partition functions of the reactants and of the activated complex.

text: Eliminating mining eliminates mine safety issues.  Compared to traditional coal mining and processing, the underground coal gasification eliminates surface damage and solid waste discharge, and reduces sulfur dioxide () and nitrogen oxide () emissions.  For comparison, the ash content of UCG syngas is estimated to be approximately 10 mg/m³ compared to smoke from traditional coal burning where ash content may be up to 70 mg/m³. However, UCG operations cannot be controlled as precisely as surface gasifiers. Variables include the rate of water influx, the distribution of reactants in the gasification zone, and the growth rate of the cavity. These can only be estimated from temperature measurements, and analyzing product gas quality and quantity.

text: Eliminating mining eliminates mine safety issues.  Compared to traditional coal mining and processing, the underground coal gasification eliminates surface damage and solid waste discharge, and reduces

text: sulfur dioxide

text: () and

text: nitrogen oxide

text: () emissions.  For comparison, the ash content of UCG syngas is estimated to be approximately 10 mg/m³ compared to smoke from traditional coal burning where ash content may be up to 70 mg/m³. However, UCG operations cannot be controlled as precisely as surface gasifiers. Variables include the rate of water influx, the distribution of reactants in the gasification zone, and the growth rate of the cavity. These can only be estimated from temperature measurements, and analyzing product gas quality and quantity.

text: Chemical reactions are central to chemical engineering where they are used for the synthesis of new compounds from natural raw materials such as petroleum and mineral ores. It is essential to make the reaction as efficient as possible, maximizing the yield and minimizing the amount of reagents, energy inputs and waste. Catalysts are especially helpful for reducing the energy required for the reaction and increasing its reaction rate.

text: Chemical reactions are central to

text: chemical engineering

text: where they are used for the synthesis of new compounds from natural raw materials such as

text: petroleum

text: and mineral

text: ore

text: s. It is essential to make the reaction as efficient as possible, maximizing the yield and minimizing the amount of reagents, energy inputs and waste.

text: Catalyst

text: s are especially helpful for reducing the energy required for the reaction and increasing its

text: reaction rate

text: Increase in temperature can speed up the desired reaction, but also speed up the decomposition of reagents and starting materials.  However, pressure can speed up the desired reaction and only impacts decomposition when it involves the release of a gas or a reaction with a gas in the vessel. When the desired reaction is accelerated, competing reactions are minimized.  Pressure generally enables faster reactions with cleaner reaction profiles.

text: Increase in temperature can speed up the desired reaction, but also speed up the

text: decomposition

text: of

text: reagent

text: s and

text: starting materials

text: .  However, pressure can speed up the desired reaction and only impacts decomposition when it involves the release of a gas or a reaction with a gas in the vessel. When the desired reaction is accelerated, competing reactions are minimized.  Pressure generally enables faster reactions with cleaner reaction profiles.

text: The initial aqueous solution contains hydrogen peroxide, an iodate, divalent manganese (Mn) as catalyst, a strong chemically unreactive acid (sulphuric acid (HSO) or perchloric acid (HClO) are good), and an organic compound with an active ("enolic") hydrogen atom attached to carbon which will slowly reduce free iodine (I) to iodide (I). (Malonic acid (CH(COOH)) is excellent for that purpose.) Starch is optionally added as an indicator to show the abrupt increase in iodide ion concentration as a sudden change from amber (free iodine) to dark blue (the "iodine-starch complex", which requires both iodine and iodide.)Recently it has been shown, however, that the starch is not only a simple indicator for iodine in the reaction. In the presence of starch the number of oscillations are higher and the period times are longer compared to the starch-free mixtures. It was also found that the iodine consumption segment within one period of oscillation is also significantly longer in the starch containing mixtures. This suggests that the starch probably acts as a reservoir for the iodine and iodide due to the starch-triiodide equilibrium, thereby modifying the kinetics of the steps in which iodine and iodide are involved. In the same study, a method was presented for minimizing the environmental impact of the reaction mixture before its disposal. The residual mixture contains iodinated malonic acid, inorganic acid, manganous catalysts, unreacted iodate and hydrogen peroxide. After the oscillations cease, the iodomalonic acid decomposes and iodine is produced. The rate of decomposition depends on the conditions. All of the components present in the residual mixture are of environmental concern: Iodate, iodine and hydrogen peroxide are strong oxidants, the acid is corrosive and manganese has been suggested to cause neurological disorders (citation needed). A simple method has been developed employing thiosulfate and carbonate – two inexpensive salts – to remove all oxidants, neutralize the acidity and recover the manganous ion in the form of manganese dioxide. The reaction is "poisoned" by chloride (Cl) ion, which must therefore be avoided, and will oscillate under a fairly wide range of initial concentrations. For recipes suitable for demonstration purposes, see Shakhashiri or Preparations in the external links.

text: The initial aqueous solution contains hydrogen peroxide, an iodate, divalent

text: manganese

text: (Mn) as

text: catalyst

text: , a strong chemically unreactive acid (

text: sulphuric acid

text: (HSO) or

text: perchloric acid

text: (HClO) are good), and an organic compound with an active

text: ("enolic")

text: hydrogen atom attached to carbon which will slowly

text: reduce

text: free iodine (I) to

text: iodide

text: (I). (

text: Malonic acid

text: (CH(COOH)) is excellent for that purpose.) Starch is optionally added as an indicator to show the abrupt increase in iodide ion concentration as a sudden change from amber (free iodine) to dark blue (the

text: "iodine-starch complex"

text: Preparations

text: in the external links.

text: There are several forms of biofuel, often manufactured using sedimentation, centrifugation, and filtration. The fats and oils are turned into esters while separating the glycerin. At the end of the process, the glycerin settles and the biofuel floats. The process through which the glycerin is separated from the biodiesel is known as transesterification. Glycerin is another by-product from Jatropha oil processing that can add value to the crop. Transesterification is a simple chemical reaction that neutralizes the free fatty acids present in any fatty substances in Jatropha. A chemical exchange takes place between the alkoxy groups of an ester compound by an alcohol. Usually, methanol and ethanol are used for the purpose. The reaction occurs by the presence of a catalyst, usually sodium hydroxide (NaOH) or caustic soda and potassium hydroxide (KOH), which forms fatty esters (e.g., methyl or ethyl esters), commonly known as biodiesel. It takes approximately 10% of methyl alcohol by weight of the fatty substance to start the transesterification process.

text: There are several forms of biofuel, often manufactured using

text: sedimentation

text: centrifugation

text: , and

text: filtration

text: . The fats and oils are turned into esters while separating the

text: glycerin

text: . At the end of the process, the glycerin settles and the biofuel floats. The process through which the glycerin is separated from the biodiesel is known as

text: transesterification

text: . Glycerin is another by-product from Jatropha oil processing that can add value to the crop. Transesterification is a simple chemical reaction that neutralizes the free fatty acids present in any fatty substances in Jatropha. A chemical exchange takes place between the

text: alkoxy

text: groups of an ester compound by an alcohol. Usually,

text: methanol

text: and

text: ethanol

text: are used for the purpose. The reaction occurs by the presence of a

text: catalyst

text: , usually sodium hydroxide (NaOH) or caustic soda and potassium hydroxide (KOH), which forms fatty esters (e.g., methyl or ethyl esters), commonly known as

text: biodiesel

text: . It takes approximately 10% of methyl alcohol by weight of the fatty substance to start the transesterification process.

text: The poisoning reaction should be viewed like any other chemical reaction between a gas phase reactant and the solid surface, where the poisoned sites are distributed throughout the catalyst pore structure as a function of poison diffusion into the catalyst and the rate of the poisoning reaction. At the two extremes, this gives rise to two scenarios. First, when the poisoning reaction rate is slow relative to the rate of diffusion, the poison will be evenly distributed throughout the catalyst and will result in homogeneous poisoning of the catalyst. Conversely, if the reaction rate is fast compared to the rate of diffusion, a poisoned shell will form on the exterior layers of the catalyst, a situation known as "pore-mouth" poisoning, and the rate of catalytic reaction may become limited by the rate of diffusion through the inactive shell.

text: The poisoning reaction should be viewed like any other chemical reaction between a gas phase reactant and the solid surface, where the poisoned sites are distributed throughout the catalyst pore structure as a function of poison diffusion into the catalyst and the rate of the poisoning reaction. At the two extremes, this gives rise to two scenarios. First, when the poisoning reaction rate is slow relative to the rate of diffusion, the poison will be evenly distributed throughout the catalyst and will result in

text: homogeneous

text: poisoning of the catalyst. Conversely, if the reaction rate is fast compared to the rate of diffusion, a poisoned shell will form on the exterior layers of the catalyst, a situation known as "pore-mouth" poisoning, and the rate of catalytic reaction may become limited by the rate of diffusion through the inactive shell.

text: The rule is very easy to apply in one's head while driving: simply divide your speed (MPH) by 10 and again by 2, then add 1. That's it! If one is going sixty mph, divide by ten to get 6, then divide by two to get 3; adding a one-second reaction time, we get that you can generally stop beyond 4 seconds of distance ahead. Drivers that require additional perception-reaction time, such as novices, elderly, or those in complex or adverse environments can benefit by adding additional seconds.

text: These high concentrations of macromolecules occupy a large proportion of the volume of the cell, which reduces the volume of solvent that is available for other macromolecules. This excluded volume effect increases the effective concentration of macromolecules (increasing their chemical activity), which in turn alters the rates and equilibrium constants of their reactions. In particular this effect alters dissociation constants by favoring the association of macromolecules, such as when multiple proteins come together to form protein complexes, or when DNA-binding proteins bind to their targets in the genome. Crowding may also affect enzyme reactions involving small molecules if the reaction involves a large change in the shape of the enzyme.

text: These high concentrations of macromolecules occupy a large proportion of the volume of the cell, which reduces the volume of solvent that is available for other macromolecules. This

text: excluded volume

text: effect increases the effective concentration of macromolecules (increasing their

text: chemical activity

text: ), which in turn alters the

text: rates

text: and

text: equilibrium constant

text: s of their reactions. In particular this effect alters

text: dissociation constant

text: s by favoring the association of macromolecules, such as when multiple proteins come together to form

text: protein complex

text: es, or when

text: DNA-binding protein

text: s bind to their targets in the

text: genome

text: . Crowding may also affect enzyme reactions involving small molecules if the reaction involves a large change in the shape of the enzyme.

text: In the Shiina esterification performed under basic conditions, asymmetric synthesis is realized using chiral nucleophilic catalysts. First, in the presence of a chiral nucleophilic catalyst, by the action of an appropriate carboxylic acid anhydride on a racemic aliphatic carboxylic acid, the corresponding MA is produced, resulting in the kinetic resolution of the racemic aliphatic carboxylic acid after having been subjected to reaction with achiral alcohol. Using this method, optically active carboxylic acids and optically active carboxylic acid esters can be obtained. It is also possible to realize the kinetic resolution of racemic alcohols by modifying the compositions of the reactants, i.e., by forming MA through reactions between achiral carboxylic acid and the appropriate carboxylic acid anhydride; then, by activating the racemic alcohols using the MA, optically active alcohols and optically active carboxylic acid esters can be obtained.

text: , the concentration of the reactant should be kept at a low level in order to maximize selectivity. This can be accomplished using a semibatch reactor.

text: The GEBIK and GEBIF equations are the most generalized approach to describe isotopic effects in any chemical, catalytic reaction and biochemical reactions because they can describe isotopic effects in equilibrium reactions, kinetic chemical reactions and kinetic biochemical reactions. In the latter two cases, they can describe both stationary and non-stationary fractionation (i.e., variable and inverse fractionation). In general, isotopic effects depend on the number of reactants and on the number of combinations resulting from the number of substitutions in all reactants and products. Describing with accuracy isotopic effects, however, depends also on the specific rate law used to describe the chemical or biochemical reaction that produces isotopic effects. Normally, regardless of whether a reaction is purely chemical or whether it involves some enzyme of biological nature, the equations used to describe isotopic effects base on first-order kinetics. This approach systematically leads to isotopic effects that can be described by means of the Rayleigh equation. In this case, isotopic effects will always be expressed as a constant, hence will not be able to describe isotopic effects in reactions where fractionation and enrichment are variable or inverse during the course of a reaction. Most chemical reactions do not follow first-order kinetics; neither biochemical reactions can normally be described with first-order kinetics. To properly describe isotopic effects in chemical or biochemical reactions, different approaches must be employed such as the use of Michaelis–Menten reaction order (for chemical reactions) or coupled Michaelis–Menten and Monod reaction orders (for biochemical reactions). However, conversely to Michaelis–Menten kinetics, GEBIK and GEBIF equations are solved under the hypothesis of non-steady state. This characteristic allows GEBIK and GEBIF to capture transient isotopic effects.

text: The GEBIK and GEBIF equations are the most generalized approach to describe isotopic effects in any

text: chemical

text: catalytic reaction

text: and

text: biochemical

text: reactions because they can describe isotopic effects in equilibrium reactions, kinetic chemical reactions and kinetic biochemical reactions. In the latter two cases, they can describe both stationary and non-stationary fractionation (i.e., variable and inverse fractionation). In general, isotopic effects depend on the number of reactants and on the number of combinations resulting from the number of substitutions in all reactants and products. Describing with accuracy isotopic effects, however, depends also on the specific

text: rate law

text: used to describe the chemical or biochemical reaction that produces isotopic effects. Normally, regardless of whether a reaction is purely chemical or whether it involves some

text: enzyme

text: of biological nature, the equations used to describe isotopic effects base on first-order kinetics. This approach systematically leads to isotopic effects that can be described by means of the Rayleigh equation. In this case, isotopic effects will always be expressed as a constant, hence will not be able to describe isotopic effects in reactions where fractionation and enrichment are variable or inverse during the course of a reaction. Most chemical reactions do not follow first-order kinetics; neither biochemical reactions can normally be described with first-order kinetics. To properly describe isotopic effects in chemical or biochemical reactions, different approaches must be employed such as the use of

text: Michaelis–Menten

text: reaction order (for chemical reactions) or coupled Michaelis–Menten and Monod reaction orders (for biochemical reactions). However, conversely to Michaelis–Menten kinetics, GEBIK and GEBIF equations are solved under the hypothesis of non-steady state. This characteristic allows GEBIK and GEBIF to capture transient isotopic effects.

text: PCET is thought to be pervasive in redox reactions that appear to be net hydrogenations and dehydrogenations. Relevant examples include water oxidation in photosynthesis, nitrogen fixation and oxygen reduction in many pathways for respiration. Inorganic chemists often study simple reactions to test this mechanism, one example being the comproportionation of a Ru(II) aquo and a Ru(IV) oxo reactants: cis-[(bipy)(py)Ru(O)] + cis-[(bipy)(py)Ru(OH)] → 2cis-[(bipy)(py)Ru(OH)]PCET is also often invoked in electrochemical reactions where reduction is coupled to protonation or where oxidation is coupled to deprotonation.

text: PCET is thought to be pervasive in redox reactions that appear to be net hydrogenations and dehydrogenations. Relevant examples include water oxidation in

text: photosynthesis

text: nitrogen fixation

text: and oxygen reduction in many pathways for

text: respiration

text: . Inorganic chemists often study simple reactions to test this mechanism, one example being the

text: comproportionation

text: of a Ru(II) aquo and a Ru(IV) oxo reactants: cis-[(

text: bipy

text: )(py)Ru(O)] + cis-[(bipy)(py)Ru(OH)] → 2cis-[(bipy)(py)Ru(OH)]PCET is also often invoked in electrochemical reactions where reduction is coupled to protonation or where oxidation is coupled to deprotonation.

text: In addition to the active metal the catalysts typically contain a number of "promoters," including potassium and copper. Group 1 alkali metals, including potassium, are a poison for cobalt catalysts but are promoters for iron catalysts. Catalysts are supported on high-surface-area binders/supports such as silica, alumina, or zeolites. Promotors also have an important influence on activity. Alkali metal oxides and copper are common promotors, but the formulation depends on the primary metal, iron vs cobalt. Alkali oxides on cobalt catalysts generally cause activity to drop severely even with very low alkali loadings. C and CO selectivity increase while methane and C–C selectivity decrease. In addition, the alkene to alkane ratio increases.

text: In addition to the active metal the catalysts typically contain a number of "promoters," including potassium and copper. Group 1 alkali metals, including potassium, are a poison for cobalt catalysts but are promoters for iron catalysts. Catalysts are supported on high-surface-area binders/supports such as

text: silica

text: alumina

text: , or

text: zeolites

text: . Promotors also have an important influence on activity. Alkali metal oxides and copper are common promotors, but the formulation depends on the primary metal, iron vs cobalt. Alkali oxides on cobalt catalysts generally cause activity to drop severely even with very low alkali loadings. C and CO selectivity increase while methane and C–C selectivity decrease. In addition, the alkene to alkane ratio increases.

text: For endothermic reactions, the type of surface determines the type of energy which is most effective in bringing about reaction. Translational energy of the reactants is most effective at inducing reactions with an attractive surface, while vibrational excitation is more effective for reactions with a repulsive surface. As an example of the latter case, the reaction F + HCl(v=1) → Cl + HF is about five times faster than F + HCl(v=0) → Cl + HF for the same total energy of HCl.

text: For

text: endothermic reactions

text: , the type of surface determines the type of energy which is most effective in bringing about reaction. Translational energy of the reactants is most effective at inducing reactions with an attractive surface, while vibrational excitation is more effective for reactions with a repulsive surface. As an example of the latter case, the reaction F + HCl(v=1) → Cl + HF is about five times faster than F + HCl(v=0) → Cl + HF for the same total energy of HCl.

text: In enzymology, a cyclomaltodextrinase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , a cyclomaltodextrinase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: Examples of reactions that are first order with respect to the reactant:

text: This definition is a special case of the concept of chain length in chemical kinetics. For any chemical chain reaction, the chain length is defined as the average number of times that the closed cycle of chain propagation steps is repeated. It is equal to the rate of the overall reaction divided by the rate of the initiation step in which the chain carriers are formed.<ref>"Chain Length." IUPAC Compendium of Chemical Terminology. 2005-2014.

text: This definition is a special case of the concept of chain length in

text: chemical kinetics

text: . For any

text: chemical chain reaction

text: , the chain length is defined as the average number of times that the closed cycle of

text: chain propagation

text: steps is repeated. It is equal to the

text: rate

text: of the overall reaction divided by the rate of the

text: initiation

text: step in which the chain carriers are formed.<ref>"Chain Length." IUPAC Compendium of Chemical Terminology. 2005-2014.

text: The effect of changing the temperature in the equilibrium can be made clear by 1) incorporating heat as either a reactant or a product, and 2) assuming that an increase in temperature increases the heat content of a system. When the reaction is exothermic (ΔH is negative, puts energy out), heat is included as a product, and, when the reaction is endothermic (ΔH is positive, takes energy in), heat is included as a reactant. Hence, whether increasing or decreasing the temperature would favor the forward or the reverse reaction can be determined by applying the same principle as with concentration changes.

text: The effect of changing the temperature in the equilibrium can be made clear by 1) incorporating heat as either a reactant or a product, and 2) assuming that an increase in temperature increases the heat content of a system. When the reaction is

text: exothermic

text: (ΔH is negative, puts energy out), heat is included as a product, and, when the reaction is

text: endothermic

text: (ΔH is positive, takes energy in), heat is included as a reactant. Hence, whether increasing or decreasing the temperature would favor the forward or the reverse reaction can be determined by applying the same principle as with concentration changes.

text: The order of a reaction for each reactant can be estimated from the variation in initial rate with the concentration of that reactant, using the natural logarithm of the typical rate equation

text: The order of a reaction for each reactant can be estimated from the variation in initial rate with the concentration of that reactant, using the

text: natural logarithm

text: of the typical rate equation

text: are the internal energy of the reactants and products respectively. In the constant volume adiabatic flame temperature case, the volume of the system is held constant hence there is no work occurring,

text: Conjugated enynes have also been used for benzannulation reactions catalyzed by cobalt. This type of benzannulation involves a [4+2] cycloaddition followed by a 1,3-hydrogen shift. In dichloromethane, the symmetrical benzannulation products are yielded but in tetrahydrofuran (THF), unsymmetrical benzannulation products were obtained with good regioselectivity.  These reactions utilize  1,3-bis(diphenylphosphino)propane (dppp) substituted cobalt catalyst in the presence of powdered zinc and zinc iodide for a solvent dependent benzannulation reaction (Scheme 11). In dichloromethane the ratio of A:B is 78:22 with an overall combined yield of 90% and in THF the ratio has switched to 7:93 (A:B) with a combined yield of 85%.

text: Conjugated

text: enyne

text: s have also been used for benzannulation reactions catalyzed by

text: cobalt

text: . This type of benzannulation involves a [4+2] cycloaddition followed by a 1,3-hydrogen shift. In

text: dichloromethane

text: , the symmetrical benzannulation products are yielded but in

text: tetrahydrofuran

text: (THF), unsymmetrical benzannulation products were obtained with good regioselectivity.  These reactions utilize

text: (dppp) substituted cobalt catalyst in the presence of powdered

text: zinc

text: and

text: zinc iodide

text: for a solvent dependent benzannulation reaction (Scheme 11). In dichloromethane the ratio of A:B is 78:22 with an overall combined yield of 90% and in THF the ratio has switched to 7:93 (A:B) with a combined yield of 85%.

text: For example, in chemical kinetics, it has been observed that ultrasound can greatly enhance chemical reactivity in a number of systems by as much as a million-fold; effectively acting as a catalyst by exciting the atomic and molecular modes of the system (such as the vibrational, rotational, and translational modes). In addition, in reactions that use solids, ultrasound breaks up the solid pieces from the energy released from the bubbles created by cavitation collapsing through them. This gives the solid reactant a larger surface area for the reaction to proceed over, increasing the observed rate of reaction.

text: For example, in

text: chemical kinetics

text: , it has been observed that ultrasound can greatly enhance chemical reactivity in a number of systems by as much as a million-fold; effectively acting as a catalyst by exciting the atomic and molecular modes of the system (such as the vibrational, rotational, and translational modes). In addition, in reactions that use solids, ultrasound breaks up the solid pieces from the energy released from the bubbles created by cavitation collapsing through them. This gives the solid reactant a larger surface area for the reaction to proceed over, increasing the observed rate of reaction.

text: It is easiest to describe the flux of metabolites through a pathway by considering the reaction steps individually. The flux of the metabolites through each reaction (J) is the rate of the forward reaction (Vf), less that of the reverse reaction (Vr).

text: A concentration cell is a limited form of a galvanic cell that has two equivalent half-cells of the same composition differing only in concentrations. One can calculate the potential developed by such a cell using the Nernst Equation. A concentration cell produces a small voltage as it attempts to reach chemical equilibrium, which occurs when the concentration of reactant in both half-cells are equal.  Because an order of magnitude concentration difference produces less than 60 millivolts at room temperature, concentration cells are not typically used for energy storage.

text: A concentration cell is a limited form of a

text: galvanic cell

text: that has two equivalent

text: half-cell

text: s of the same composition differing only in concentrations. One can calculate the potential developed by such a cell using the

text: Nernst Equation

text: . A concentration cell produces a small

text: voltage

text: as it attempts to reach

text: chemical equilibrium

text: , which occurs when the concentration of reactant in both half-cells are equal.  Because an order of magnitude concentration difference produces less than 60 millivolts at room temperature, concentration cells are not typically used for energy storage.

text: In electrochemistry, concentration polarization denotes the part of the polarization of an electrolytic cell resulting from changes in the electrolyte concentration due to the passage of current through the electrode/solution interface. Here polarization is understood as the shift of the Electrochemical potential difference across the cell from its equilibrium value. When the term is used in this sense, it is equivalent to “concentration overpotential”. The cause of the changes in concentration (emergence of concentration gradients in the solution adjacent to the electrode surface) is the difference in the rate of electrochemical reaction at the electrode and the rate of ion migration in the solution from/to the surface. When a chemical species participating in an electrochemical electrode reaction is in short supply, the concentration of this species at the surface decreases causing diffusion, which is added to the migration transport towards the surface in order to maintain the balance of consumption and delivery of that species.

text: In

text: electrochemistry

text: , concentration polarization denotes the part of the

text: polarization

text: of an

text: electrolytic cell

text: resulting from changes in the electrolyte concentration due to the passage of current through the electrode/solution interface. Here polarization is understood as the shift of the

text: Electrochemical potential

text: difference across the cell from its equilibrium value. When the term is used in this sense, it is equivalent to “

text: concentration overpotential

text: ”. The cause of the changes in concentration (emergence of concentration gradients in the solution adjacent to the electrode surface) is the difference in the rate of electrochemical reaction at the electrode and the rate of ion migration in the solution from/to the surface. When a chemical species participating in an electrochemical electrode reaction is in short supply, the concentration of this species at the surface decreases causing diffusion, which is added to the migration transport towards the surface in order to maintain the balance of consumption and delivery of that species.

text: At a modified electrode, an oxidation-reduction substance accomplishes electrocatalysis by transferring electrons from the electrode to a reactant, or a reaction substrate.

text: At a modified electrode, an

text: oxidation-reduction

text: substance accomplishes

text: electrocatalysis

text: by transferring electrons from the electrode to a reactant, or a reaction

text: substrate

text: The rate equation shows the detailed dependence of the reaction rate on the concentrations of reactants and other species present. Different mathematical forms are possible depending on the reaction mechanism. The actual rate equation for a given reaction is determined experimentally and provides information about the reaction mechanism.

text: The

text: rate equation

text: shows the detailed dependence of the reaction rate on the concentrations of reactants and other species present. Different mathematical forms are possible depending on the

text: reaction mechanism

text: . The actual rate equation for a given reaction is determined experimentally and provides information about the reaction mechanism.

text: In chemistry, J. H. van't Hoff (1884) came up with the idea that equilibrium has dynamical nature and is a result of the balance between the forward and backward reaction rates. He did not study reaction mechanisms with many elementary reactions and could not formulate the principle of detailed balance for complex reactions. In 1901, Rudolf Wegscheider introduced the principle of detailed balance for complex chemical reactions. He found that for a complex reaction the principle of detailed balance implies important and non-trivial relations between reaction rate constants for different reactions. In particular, he demonstrated that the irreversible cycles of reaction are impossible and for the reversible cycles the product of constants of the forward reactions (in the "clockwise" direction) is equal to the product of constants of the reverse reactions (in the "anticlockwise" direction). Lars Onsager (1931) used these relations in his well known work, without direct citation but with the following remark:

text: In chemistry,

text: J. H. van't Hoff

text: (1884) came up with the idea that equilibrium has dynamical nature and is a result of the balance between the forward and backward reaction rates. He did not study reaction mechanisms with many elementary reactions and could not formulate the principle of detailed balance for complex reactions. In 1901,

text: Rudolf Wegscheider

text: introduced the principle of detailed balance for complex chemical reactions. He found that for a complex reaction the principle of detailed balance implies important and non-trivial relations between reaction rate constants for different reactions. In particular, he demonstrated that the irreversible cycles of reaction are impossible and for the reversible cycles the product of constants of the forward reactions (in the "clockwise" direction) is equal to the product of constants of the reverse reactions (in the "anticlockwise" direction).

text: Lars Onsager

text: (1931) used these relations in his well known work, without direct citation but with the following remark:

text: J. W. Gibbs suggested in 1873 that equilibrium is attained when the Gibbs free energy of the system is at its minimum value (assuming the reaction is carried out at constant temperature and pressure). What this means is that the derivative of the Gibbs energy with respect to reaction coordinate (a measure of the extent of reaction that has occurred, ranging from zero for all reactants to a maximum for all products) vanishes, signalling a stationary point. This derivative is called the reaction Gibbs energy (or energy change) and corresponds to the difference between the chemical potentials of reactants and products at the composition of the reaction mixture. This criterion is both necessary and sufficient. If a mixture is not at equilibrium, the liberation of the excess Gibbs energy (or Helmholtz energy at constant volume reactions) is the "driving force" for the composition of the mixture to change until equilibrium is reached. The equilibrium constant can be related to the standard Gibbs free energy change for the reaction by the equation

text: J. W. Gibbs

text: suggested in 1873 that equilibrium is attained when the

text: Gibbs free energy

text: of the system is at its minimum value (assuming the reaction is carried out at constant temperature and pressure). What this means is that the derivative of the Gibbs energy with respect to

text: reaction coordinate

text: (a measure of the

text: extent of reaction

text: that has occurred, ranging from zero for all reactants to a maximum for all products) vanishes, signalling a

text: stationary point

text: . This derivative is called the reaction Gibbs energy (or energy change) and corresponds to the difference between the

text: chemical potential

text: s of reactants and products at the composition of the reaction mixture. This criterion is both necessary and sufficient. If a mixture is not at equilibrium, the liberation of the excess Gibbs energy (or

text: Helmholtz energy

text: at constant volume reactions) is the "driving force" for the composition of the mixture to change until equilibrium is reached. The equilibrium constant can be related to the standard

text: Gibbs free energy

text: change for the reaction by the equation

text: PEMFCs are built out of membrane electrode assemblies (MEA) which include the electrodes, electrolyte, catalyst, and gas diffusion layers. An ink of catalyst, carbon, and electrode are sprayed or painted onto the solid electrolyte and carbon paper is hot pressed on either side to protect the inside of the cell and also act as electrodes. The pivotal part of the cell is the triple phase boundary (TPB) where the electrolyte, catalyst, and reactants mix and thus where the cell reactions actually occur. Importantly, the membrane must not be electrically conductive so the half reactions do not mix. Operating temperatures above 100 °C are desired  so the water byproduct becomes steam and water management becomes less critical in cell design.

text: PEMFCs are built out of

text: membrane electrode assemblies

text: (MEA) which include the electrodes, electrolyte, catalyst, and gas diffusion layers. An ink of catalyst, carbon, and electrode are sprayed or painted onto the solid electrolyte and carbon paper is hot pressed on either side to protect the inside of the cell and also act as electrodes. The pivotal part of the cell is the triple phase boundary (TPB) where the electrolyte, catalyst, and reactants mix and thus where the cell reactions actually occur. Importantly, the membrane must not be electrically conductive so the half reactions do not mix. Operating temperatures above 100 °C are desired  so the water byproduct becomes steam and water management becomes less critical in cell design.

text: Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor

text: Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the

text: activation energy

text: . The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor

text: Regardless of the equation format, the heat of formation of a compound at any temperature is ΔH° at 298.15 K, plus the sum of the heat content parameters of the products minus the sum of the heat content parameters of the reactants. The C equation is obtained by taking the derivative of the heat content equation.

text: Potential energy surfaces for chemical reactions can be classified as attractive or repulsive by comparing the extensions of the bond lengths in the activated complex relative to those of the reactants and products. For a reaction of type A + B—C → A—B + C, the bond length extension for the newly formed A—B bond is defined as R* = R − R, where R is the A—B bond length in the transition state and R in the product molecule. Similarly for the bond which is broken in the reaction, R* = R − R, where R refers to the reactant molecule.

text: The physical state (solid, liquid, or gas) of a reactant is also an important factor of the rate of change. When reactants are in the same phase, as in aqueous solution, thermal motion brings them into contact. However, when they are in different phases, the reaction is limited to the interface between the reactants. Reaction can occur only at their area of contact; in the case of a liquid and a gas, at the surface of the liquid. Vigorous shaking and stirring may be needed to bring the reaction to completion. This means that the more finely divided a solid or liquid reactant the greater its surface area per unit volume and the more contact it with the other reactant, thus the faster the reaction. To make an analogy, for example, when one starts a fire, one uses wood chips and small branches — one does not start with large logs right away. In organic chemistry, on water reactions are the exception to the rule that homogeneous reactions take place faster than heterogeneous reactions.

text: The

text: physical state

text: solid

text: liquid

text: , or

text: gas

text: ) of a reactant is also an important factor of the rate of change. When reactants are in the same

text: phase

text: , as in

text: aqueous

text: solution

text: , thermal motion brings them into contact. However, when they are in different phases, the reaction is limited to the interface between the reactants. Reaction can occur only at their area of contact; in the case of a liquid and a gas, at the surface of the liquid. Vigorous shaking and stirring may be needed to bring the reaction to completion. This means that the more finely divided a solid or liquid reactant the greater its

text: surface area

text: per unit

text: volume

text: and the more contact it with the other reactant, thus the faster the reaction. To make an analogy, for example, when one starts a fire, one uses wood chips and small branches — one does not start with large logs right away. In organic chemistry,

text: on water reaction

text: s are the exception to the rule that homogeneous reactions take place faster than heterogeneous reactions.

text: In chemistry, dynamic stereochemistry studies the effect of stereochemistry on the reaction rate of a chemical reaction. Stereochemistry is involved in:

text: In

text: chemistry

text: , dynamic stereochemistry studies the effect of

text: stereochemistry

text: on the

text: reaction rate

text: of a

text: chemical reaction

text: . Stereochemistry is involved in:

text: In the presence of 10-20 % chiral catalyst, 80–90% ee is achievable.

text: In the presence of 10-20 % chiral catalyst, 80–90%

text: ee

text: is achievable.

text: Some enzymes can carry out thousands of chemical reactions each second. However, RuBisCO is slow, being able to fix only 3-10 carbon dioxide molecules each second per molecule of enzyme.  The reaction catalyzed by RuBisCO is, thus, the primary rate-limiting factor of the Calvin cycle during the day. Nevertheless, under most conditions, and when light is not otherwise limiting photosynthesis, the speed of RuBisCO responds positively to increasing carbon dioxide concentration.However, our descriptive knowledge will become more usable when we can translate them into quantitative models that can enable us to calculate the outcome of the reaction under a given condition.  Since RubisCO reacts with RuBP (ribulose 1,5 bisphosphate) first to produces enediol and next with  that after some intermediate changes produces PGA (3-phosphoglycerate), a biochemical model is developed   to represent the  effects of  these steps quantitatively. Since carboxylation or fixation of  is possible only after the synthesis of enediol, thus it is suggested that the role of RubisCO is to produce enediol that is carboxylase and oxygenase (EnCO). Accordingly, RubisCO is called enolase-phosphglycerase (EPGase) since it is neither carboxylase nor oxygenase.

text: Hollow spheres and porous particles (e.g. glass shells/spheres, epoxide shells, PVDC shells, fly ash, vermiculite, other reticulated materials) are mixed and dispersed in the liquid reactants, which are then shaped into a solid polymer part containing a network of voids.

text: Hollow spheres and porous particles (e.g. glass shells/spheres, epoxide shells, PVDC shells,

text: fly ash

text: vermiculite

text: , other reticulated materials) are mixed and dispersed in the liquid reactants, which are then shaped into a solid polymer part containing a network of voids.

text: As noted above, variants that deviate from this template are known; what designates a Nazarov cyclization in particular is the generation of the pentadienyl cation followed by electrocyclic ring closure to an oxyallyl cation. In order to achieve this transformation, the molecule must be in the s-trans/s-trans conformation, placing the vinyl groups in an appropriate orientation. The propensity of the system to enter this conformation dramatically influences reaction rate, with α-substituted substrates having an increased population of the requisite conformer due to allylic strain. Coordination of an electron donating α-substituent by the catalyst can likewise increase the reaction rate by enforcing this conformation.

text: As noted above, variants that deviate from this template are known; what designates a Nazarov cyclization in particular is the generation of the pentadienyl

text: cation

text: followed by electrocyclic ring closure to an oxyallyl cation. In order to achieve this transformation, the molecule must be in the s-trans/s-trans

text: conformation

text: , placing the

text: vinyl

text: groups in an appropriate orientation. The propensity of the system to enter this conformation dramatically influences

text: reaction rate

text: , with α-substituted substrates having an increased population of the requisite

text: conformer

text: due to

text: allylic strain

text: . Coordination of an electron donating α-substituent by the catalyst can likewise increase the reaction rate by enforcing this conformation.

text: The mechanisms of chemical reactions can be investigated by observing how the kinetics of a reaction is changed by making an isotopic modification of a substrate, known as the kinetic isotope effect. This is now a standard method in organic chemistry. Briefly, replacing normal hydrogen (protons) by deuterium within a molecule causes the molecular vibrational frequency of X-H (for example C-H, N-H and O-H) bonds to decrease, which leads to a decrease in vibrational zero-point energy. This can lead to a decrease in the reaction rate if the rate-determining step involves breaking a bond between hydrogen and another atom. Thus, if the reaction changes in rate when protons are replaced by deuteriums, it is reasonable to assume that the breaking of the bond to hydrogen is part of the step which determines the rate.

text: The mechanisms of chemical reactions can be investigated by observing how the kinetics of a reaction is changed by making an isotopic modification of a substrate, known as the

text: kinetic isotope effect

text: . This is now a standard method in

text: organic chemistry

text: . Briefly, replacing normal hydrogen (

text: protons

text: ) by

text: deuterium

text: within a molecule causes the

text: molecular vibration

text: al frequency of X-H (for example C-H, N-H and O-H) bonds to decrease, which leads to a decrease in vibrational

text: zero-point energy

text: . This can lead to a decrease in the reaction rate if the rate-determining step involves breaking a bond between hydrogen and another atom. Thus, if the reaction changes in rate when protons are replaced by deuteriums, it is reasonable to assume that the breaking of the bond to hydrogen is part of the step which determines the rate.

text: An explosion is a type of spontaneous chemical reaction that, once initiated, is driven by both a large exothermic change (great release of heat) and a large positive entropy change (great quantities of gases are released) in going from reactants to products, thereby constituting a thermodynamically favorable process in addition to one that propagates very rapidly. Thus, explosives are substances that contain a large amount of energy stored in chemical bonds. The energetic stability of the gaseous products and hence their generation comes from the formation of strongly bonded species like carbon monoxide, carbon dioxide, and (di)nitrogen, which contain strong double and triple bonds having bond strengths of nearly 1 MJ/mole. Consequently, most commercial explosives are organic compounds containing -NO, -ONO and -NHNO groups that, when detonated, release gases like the aforementioned (e.g., nitroglycerin, TNT, HMX, PETN, nitrocellulose).

text: An explosion is a type of spontaneous chemical reaction that, once initiated, is driven by both a large exothermic change (great release of heat) and a large positive

text: entropy

text: change (great quantities of gases are released) in going from reactants to products, thereby constituting a thermodynamically favorable process in addition to one that propagates very rapidly. Thus, explosives are substances that contain a large amount of energy stored in

text: chemical bonds

text: . The energetic stability of the gaseous products and hence their generation comes from the formation of strongly bonded species like carbon monoxide, carbon dioxide, and (di)nitrogen, which contain strong double and triple bonds having bond strengths of nearly 1 MJ/mole. Consequently, most commercial explosives are organic compounds containing

text: -NO

text: -ONO

text: and

text: -NHNO

text: groups that, when detonated, release gases like the aforementioned (e.g.,

text: nitroglycerin

text: TNT

text: HMX

text: PETN

text: nitrocellulose

text: The water gas shift reaction is a moderately exothermic reversible reaction. Therefore with increasing temperature the reaction rate increases but the conversion of reactants to products becomes less favorable. Due to its exothermic nature, high carbon monoxide conversion is thermodynamically favored at low temperatures. Despite the thermodynamic favorability at low temperatures, the reaction is kinetically favored at high temperatures. The water-gas shift reaction is sensitive to temperature, with the tendency to shift towards reactants as temperature increases due to Le Chatelier's principle. Over the temperature range 600 – 2000 K, the logarithm of the equilibrium constant for the WGSR is given by the following equation:

text: The water gas shift reaction is a moderately

text: exothermic

text: reversible reaction. Therefore with increasing temperature the reaction rate increases but the conversion of reactants to products becomes less favorable. Due to its exothermic nature, high carbon monoxide conversion is

entity_name: Thermodynamic versus kinetic reaction control

text: thermodynamically

text: favored at low temperatures. Despite the thermodynamic favorability at low temperatures, the reaction is

text: kinetically

text: favored at high temperatures. The water-gas shift reaction is

text: sensitive to temperature

text: , with the tendency to shift towards reactants as temperature increases due to

text: Le Chatelier's principle

text: . Over the temperature range 600 – 2000 K, the logarithm of the equilibrium constant for the WGSR is given by the following equation:

text: Stoichiometry rests upon the very basic laws that help to understand it better, i.e., law of conservation of mass, the law of definite proportions (i.e., the law of constant composition), the law of multiple proportions and the law of reciprocal proportions. In general, chemical reactions combine in definite ratios of chemicals. Since chemical reactions can neither create nor destroy matter, nor transmute one element into another, the amount of each element must be the same throughout the overall reaction. For example, the number of atoms of a given element X on the reactant side must equal the number of atoms of that element on the product side, whether or not all of those atoms are actually involved in a reaction.

text: Stoichiometry rests upon the very basic laws that help to understand it better, i.e.,

text: law of conservation of mass

text: , the

text: law of definite proportions

text: (i.e., the

text: law of constant composition

text: ), the

text: law of multiple proportions

text: and the

text: law of reciprocal proportions

text: . In general, chemical reactions combine in definite ratios of chemicals. Since chemical reactions can neither create nor destroy matter, nor

text: transmute

text: one element into another, the amount of each element must be the same throughout the overall reaction. For example, the number of atoms of a given element X on the reactant side must equal the number of atoms of that element on the product side, whether or not all of those atoms are actually involved in a reaction.

text: The binding and inactivation steps of this reaction are investigated by incubating the enzyme with inhibitor and assaying the amount of activity remaining over time. The activity will be decreased in a time-dependent manner, usually following exponential decay. Fitting these data to a rate equation gives the rate of inactivation at this concentration of inhibitor. This is done at several different concentrations of inhibitor. If a reversible EI complex is involved the inactivation rate will be saturable and fitting this curve will give k and K.

text: The binding and inactivation steps of this reaction are investigated by incubating the enzyme with inhibitor and assaying the amount of activity remaining over time. The activity will be decreased in a time-dependent manner, usually following

text: exponential decay

text: . Fitting these data to a

text: rate equation

text: gives the rate of inactivation at this concentration of inhibitor. This is done at several different concentrations of inhibitor. If a reversible EI complex is involved the inactivation rate will be saturable and fitting this curve will give k and K.

text: The rate law or rate equation for a chemical reaction is an equation that links the reaction rate with concentrations or pressures of reactants and constant parameters (normally rate coefficients and partial reaction orders). For many reactions the rate is given by a power law such as

text: The rate law or rate equation for a

text: chemical reaction

text: is an equation that links the

text: reaction rate

text: with concentrations or pressures of reactants and constant parameters (normally rate coefficients and partial

text: reaction order

text: s). For many reactions the rate is given by a power law such as

text: Superheated water, along with supercritical water, has been used to oxidise hazardous material in the wet oxidation process. Organic compounds are rapidly oxidised without the production of toxic materials sometimes produced by combustion. However, when the oxygen levels are lower, organic compounds can be quite stable in superheated water. As the concentration of hydronium () and hydroxide () ions are 100 times larger than in water at 25 °C, superheated water can act as a stronger acid and a stronger base, and many different types of reaction can be carried out. An example of a selective reaction is oxidation of ethylbenzene to acetophenone, with no evidence of formation of phenylethanoic acid, or of pyrolysis products. Several different types of reaction in which water was behaving as reactant, catalyst and solvent were described by Katritzky et al.Triglycerides can be hydrolysed to free fatty acids and glycerol by superheated water at 275 °C,which can be the first in a two-stage process to make biodiesel.Superheated water can be used to chemically convert organic material into fuel products. This is known by several terms, including direct hydrothermal liquefaction, and hydrous pyrolysis. A few commercial scale applications exist. Thermal depolymerization or thermal conversion (TCC) uses superheated water at about 250 °C to convert turkey waste into a light fuel oil and is said to process 200 tons of low grade waste into fuel oil a day.The initial product from the hydrolysis reaction is de-watered and further processed by dry cracking at 500 °C. The “SlurryCarb” process operated by EnerTech uses similar technology to decarboxylate wet solid biowaste, which can then be physically dewatered and used as a solid fuel called E-Fuel. The plant at Rialto is said to be able to process 683 tons of waste per day.The HTU or Hydro Thermal Upgrading process appears similar to the first stage of the TCC process.  A demonstration plant is due to start up in The Netherlands said to be capable of processing 64 tons of biomass (dry basis) per day into oil.

text: Superheated water, along with

text: supercritical water

text: , has been used to oxidise hazardous material in the wet oxidation process. Organic compounds are rapidly

text: oxidised

text: without the production of toxic materials sometimes produced by combustion. However, when the oxygen levels are lower, organic compounds can be quite stable in superheated water. As the concentration of

text: hydronium

text: () and

text: hydroxide

text: () ions are 100 times larger than in water at 25 °C, superheated water can act as a stronger

text: acid

text: and a stronger

text: base

text: , and many different types of reaction can be carried out. An example of a selective reaction is oxidation of

text: ethylbenzene

text: to

text: acetophenone

text: , with no evidence of formation of phenylethanoic acid, or of

text: pyrolysis

text: products. Several different types of reaction in which water was behaving as reactant, catalyst and solvent were described by Katritzky et al.

text: Triglycerides

text: can be hydrolysed to

text: free fatty acids

text: and

text: glycerol

text: by superheated water at 275 °C,which can be the first in a two-stage process to make

text: biodiesel

text: .Superheated water can be used to chemically convert organic material into fuel products. This is known by several terms, including direct hydrothermal liquefaction, and

text: hydrous pyrolysis

text: . A few commercial scale applications exist.

text: Thermal depolymerization

text: or thermal conversion (TCC) uses superheated water at about 250 °C to convert turkey waste into a light

text: fuel oil

text: and is said to process 200 tons of low grade waste into fuel oil a day.The initial product from the hydrolysis reaction is de-watered and further processed by dry cracking at 500 °C. The “SlurryCarb” process operated by EnerTech uses similar technology to decarboxylate wet solid biowaste, which can then be physically dewatered and used as a solid fuel called E-Fuel. The plant at

text: Rialto

text: is said to be able to process 683 tons of waste per day.The HTU or Hydro Thermal Upgrading process appears similar to the first stage of the TCC process.  A demonstration plant is due to start up in The Netherlands said to be capable of processing 64 tons of biomass (

text: dry basis

text: ) per day into oil.

text: In a prototypical ALD process, a substrate is exposed to two reactants A and B in a sequential, non-overlapping way. In contrast to other techniques such as chemical vapor deposition (CVD), where thin film growth proceeds on a steady-state fashion, in ALD each reactant reacts with the surface in a self-limited way: the reactant molecules can react only with a finite number of reactive sites on the surface. Once all those sites have been consumed in the reactor, the growth stops. The remaining reactant molecules are flushed away and only then reactant B is inserted into the reactor. By alternating exposures of A and B, a thin film is deposited. This process is shown in the side figure. Consequently, when describing an ALD process one refers to both dose times (the time a surface is being exposed to a precursor) and purge times (the time left in between doses for the precursor to evacuate the chamber) for each precursor. The dose-purge-dose-purge sequence of a binary ALD process constitutes an ALD cycle. Also, rather than using the concept of growth rate, ALD processes are described in terms of their growth per cycle.

text: In a prototypical ALD process, a substrate is exposed to two reactants A and B in a sequential, non-overlapping way. In contrast to other techniques such as

text: chemical vapor deposition

text: (CVD), where thin film growth proceeds on a steady-state fashion, in ALD each reactant reacts with the surface in a self-limited way: the reactant molecules can react only with a finite number of reactive sites on the surface. Once all those sites have been consumed in the reactor, the growth stops. The remaining reactant molecules are flushed away and only then reactant B is inserted into the reactor. By alternating exposures of A and B, a thin film is deposited. This process is shown in the side figure. Consequently, when describing an ALD process one refers to both dose times (the time a surface is being exposed to a precursor) and purge times (the time left in between doses for the precursor to evacuate the chamber) for each precursor. The dose-purge-dose-purge sequence of a binary ALD process constitutes an ALD cycle. Also, rather than using the concept of growth rate, ALD processes are described in terms of their growth per cycle.

text: The solvent used in substitution reactions inherently determines the nucleophilicity of the nucleophile; this fact has become increasingly more apparent as more reactions are performed in the gas phase. As such, solvent conditions significantly affect the performance of a reaction with certain solvent conditions favoring one reaction mechanism over another.  For S1 reactions the solvent's ability to stabilize the intermediate carbocation is of direct importance to its viability as a suitable solvent.  The ability of polar solvents to increase the rate of S1 reactions is a result of the polar solvent's solvating the reactant intermediate species, i.e., the carbocation, thereby decreasing the intermediate energy relative to the starting material.  The following table shows the relative solvolysis rates of tert-butyl chloride with acetic acid (CHCOH), methanol (CHOH), and water (HO).

text: The solvent used in

text: substitution reactions

text: inherently determines the nucleophilicity of the

text: nucleophile

text: ; this fact has become increasingly more apparent as more reactions are performed in the gas phase. As such, solvent conditions significantly affect the performance of a reaction with certain solvent conditions favoring one reaction mechanism over another.  For

text: S1 reactions

text: the solvent's ability to stabilize the intermediate

text: carbocation

text: is of direct importance to its viability as a suitable solvent.  The ability of polar solvents to increase the rate of S1 reactions is a result of the polar solvent's solvating the reactant intermediate species, i.e., the carbocation, thereby decreasing the intermediate energy relative to the starting material.  The following table shows the relative solvolysis rates of tert-butyl chloride with acetic acid (CHCOH), methanol (CHOH), and water (HO).

text: In principle, the time evolution of the reactant and product concentrations can be determined from the set of simultaneous rate equations for the individual steps of the mechanism, one for each step. However the analytical solution of these differential equations is not always easy, and in some cases numerical integration may even be required. The hypothesis of a single rate-determining step can greatly simplify the mathematics. In the simplest case the initial step is the slowest, and the overall rate is just the rate of the first step.

text: In principle, the time evolution of the reactant and product concentrations can be determined from the set of simultaneous rate equations for the individual steps of the mechanism, one for each step. However the analytical solution of these

text: differential equation

text: s is not always easy, and in some cases

entity_name: Numerical methods for ordinary differential equations

text: numerical integration

text: may even be required. The hypothesis of a single rate-determining step can greatly simplify the mathematics. In the simplest case the initial step is the slowest, and the overall rate is just the rate of the first step.

text: The simplest inorganic reaction is double displacement when in mixing of two salts the ions are swapped without a change in oxidation state. In redox reactions one reactant, the oxidant, lowers its oxidation state and another reactant, the reductant, has its oxidation state increased. The net result is an exchange of electrons. Electron exchange can occur indirectly as well, e.g., in batteries, a key concept in electrochemistry.

text: The simplest

text: inorganic reaction

text: is

text: double displacement

text: when in mixing of two salts the ions are swapped without a change in oxidation state. In

text: redox reaction

text: s one reactant, the oxidant, lowers its oxidation state and another reactant, the reductant, has its oxidation state increased. The net result is an exchange of

text: electron

text: s. Electron exchange can occur indirectly as well, e.g., in

text: batteries

text: , a key concept in

text: electrochemistry

text: As with all catalysts, enzymes do not alter the position of the chemical equilibrium of the reaction. In the presence of an enzyme, the reaction runs in the same direction as it would without the enzyme, just more quickly. For example, carbonic anhydrase catalyzes its reaction in either direction depending on the concentration of its reactants:

text: As with all catalysts, enzymes do not alter the position of the chemical equilibrium of the reaction. In the presence of an enzyme, the reaction runs in the same direction as it would without the enzyme, just more quickly. For example,

text: carbonic anhydrase

text: catalyzes its reaction in either direction depending on the concentration of its reactants:

text: In the previous examples the rate determining step was one of the sequential chemical reactions leading to a product. The rate-determining step can also be the transport of reactants to where they can interact and form the product. This case is referred to as diffusion control and, in general, occurs when the formation of product from the activated complex is very rapid and thus the provision of the supply of reactants is rate determining.

text: In the previous examples the rate determining step was one of the sequential chemical reactions leading to a product. The rate-determining step can also be the transport of reactants to where they can interact and form the product. This case is referred to as

text: diffusion control

text: and, in general, occurs when the formation of product from the activated complex is very rapid and thus the provision of the supply of reactants is rate determining.

text: The units of the pre-exponential factor  are identical to those of the rate constant and will vary depending on the order of the reaction. If the reaction is first order it has the units: s, and for that reason it is often called the frequency factor or attempt frequency of the reaction. Most simply,  is the number of collisions that result in a reaction per second,  is the number of collisions (leading to a reaction or not) per second occurring with the proper orientation to react and

text: The units of the pre-exponential factor  are identical to those of the rate constant and will vary depending on the order of the reaction. If the reaction is first order it has the units:

text: s

text: , and for that reason it is often called the

text: frequency

text: factor or attempt frequency of the reaction. Most simply,  is the number of collisions that result in a reaction per second,  is the number of collisions (leading to a reaction or not) per second occurring with the proper orientation to react and

text: Chemical propulsion systems use a chemical reaction to produce a high-pressure, high-temperature gas that accelerates out of a nozzle. Chemical propellant can be liquid, solid or a hybrid of both. Liquid propellants can be a monopropellant passed through a catalyst, or bipropellant which combusts an oxidizer and a fuel. The benefits of monopropellants are relatively low-complexity/high-thrust output, low power requirements, and high reliability. Monopropellant motors tend to have high thrust while remaining comparatively simple, which also provides high reliability. These motors are practical for CubeSats due to their low power requirements and because their simplicity allows them to be very small. Small hydrazine fueled motors have been developed, but may require a waiver to fly due to restrictions on hazardous chemicals set forth in the CubeSat Design Specification. Safer chemical propellants which would not require hazardous chemical waivers are being developed, such as AF-M315 (hydroxylammonium nitrate) for which motors are being or have been designed. A "Water Electrolysis Thruster" is technically a chemical propulsion system, as it burns hydrogen and oxygen which it generates by on-orbit electrolysis of water.

text: Chemical propulsion

text: systems use a chemical reaction to produce a high-pressure, high-temperature gas that accelerates out of a

text: nozzle

text: . Chemical propellant can be liquid, solid or a hybrid of both. Liquid propellants can be a

text: monopropellant

text: passed through a

text: catalyst

text: , or

text: bipropellant

text: which

text: combusts

text: an

text: oxidizer

text: and a

text: fuel

text: . The benefits of

text: monopropellants

text: are relatively low-complexity/high-thrust output, low power requirements, and high reliability. Monopropellant motors tend to have high thrust while remaining comparatively simple, which also provides high reliability. These motors are practical for CubeSats due to their low power requirements and because their simplicity allows them to be very small. Small

text: hydrazine

text: fueled motors have been developed, but may require a waiver to fly due to restrictions on hazardous chemicals set forth in the CubeSat Design Specification. Safer chemical propellants which would not require hazardous chemical waivers are being developed, such as AF-M315 (

text: hydroxylammonium nitrate

text: ) for which motors are being or have been designed. A "Water Electrolysis Thruster" is technically a chemical propulsion system, as it burns

text: hydrogen

text: and

text: oxygen

text: which it generates by on-orbit

text: electrolysis of water

text: Although catalytic reactors are often implemented as plug flow reactors, their analysis requires more complicated treatment. The rate of a catalytic reaction is proportional to the amount of catalyst the reagents contact, as well as the concentration of the reactants. With a solid phase catalyst and fluid phase reagents, this is proportional to the exposed area, efficiency of diffusion of reagents in and products out, and efficacy of mixing. Perfect mixing usually cannot be assumed. Furthermore, a catalytic reaction pathway often occurs in multiple steps with intermediates that are chemically bound to the catalyst; and as the chemical binding to the catalyst is also a chemical reaction, it may affect the kinetics. Catalytic reactions often display the so-called falsified kinetics, i.e. the apparent kinetics differ from elementary chemical kinetics due to physical transport effects.

text: Although

text: catalytic

text: reactors are often implemented as plug flow reactors, their analysis requires more complicated treatment. The rate of a catalytic reaction is proportional to the amount of catalyst the reagents contact, as well as the concentration of the reactants. With a solid phase catalyst and fluid phase reagents, this is proportional to the exposed area, efficiency of diffusion of reagents in and products out, and efficacy of mixing. Perfect mixing usually cannot be assumed. Furthermore, a catalytic reaction pathway often occurs in multiple steps with intermediates that are chemically bound to the catalyst; and as the chemical binding to the catalyst is also a chemical reaction, it may affect the kinetics. Catalytic reactions often display the so-called falsified kinetics, i.e. the apparent kinetics differ from elementary chemical kinetics due to physical transport effects.

text: Far from equilibrium, the forward and reverse reaction rates no longer balance and the concentration of reactants and products is no longer constant. For every forward reaction

text: Beryllium oxide (BeO), also known as beryllia, is an inorganic compound with the formula BeO. This colourless solid is a notable electrical insulator with a higher thermal conductivity than any other non-metal except diamond, and exceeds that of most metals. As an amorphous solid, beryllium oxide is white. Its high melting point leads to its use as a refractory. It occurs in nature as the mineral bromellite. Historically and in materials science, beryllium oxide was called glucina or glucinium oxide. Formation of BeO from beryllium and oxygen releases the highest energy per mass of reactants for any chemical reaction, close to 24 MJ/kg.

text: Beryllium

text: oxide (BeO), also known as beryllia, is an

text: inorganic compound

text: with the

text: formula

text: BeO. This colourless solid is a notable electrical insulator with a higher thermal conductivity than any other non-metal except

text: diamond

text: , and exceeds that of most metals. As an amorphous solid, beryllium oxide is white. Its high melting point leads to its use as a

text: refractory

text: . It occurs in nature as the mineral

text: bromellite

text: . Historically and in materials science, beryllium oxide was called glucina or glucinium oxide. Formation of BeO from beryllium and oxygen releases

text: the highest energy per mass of reactants

text: for any chemical reaction, close to 24 MJ/kg.

text: The kinetic isotope effect is the difference in the rate of a chemical reaction when an atom in one of the reactants is replaced by one of its isotopes.

text: The

text: kinetic isotope effect

text: is the difference in the rate of a chemical reaction when an atom in one of the reactants is replaced by one of its

text: isotope

text: s.

text: is the reactant concentration at the particle surface, and

text: Catalysts are widely used in various chemical reactions. The activity, stability, selectivity, and regeneration ability are the most important properties to be considered in catalyst design.

text: Catalysts

text: are widely used in various

text: chemical reaction

text: s. The activity, stability, selectivity, and regeneration ability are the most important properties to be considered in catalyst design.

text: Consider a coupled set of two autocatalytic reactions in which the concentration of one of the reactants A is much larger than its equilibrium value. In this case the forward reaction rate is so much larger than the reverse rates that we can neglect the reverse rates.

text: Her contributions to surface science include discovery of collision induced processes at surfaces, in which an energetic, neutral, noble gas atom impinges on a surface pre-covered with an adsorbate, causing a reaction to occur between the surface and the adsorbate.  The reactions observed include dissociation, desorption, and absorption into the bulk of the substrate.  In addition, she discovered that electron energy loss spectroscopy can be used to detect species absorbed in the bulk of a substrate, and can be used to differentiate between bulk and surface species.  This paved the way for her discovery that hydrogen atoms absorbed in the bulk of a nickel sample are the key reactant in the hydrogenation of unsaturated hydrocarbons.  Another major discovery involved the reaction of fluorine molecules with a silicon surface (a reaction that is key to semiconductor device etching), in which the silicon surface abstracts a fluorine atom from the incident fluorine molecule, and the remaining fluorine atom scatters into the gas phase.  This is the reverse of the Eley-Rideal mechanism, one of the fundamental mechanism of gas-surface chemical reactions.

text: Her contributions to

text: surface science

text: include discovery of collision induced processes at surfaces, in which an energetic, neutral, noble gas atom impinges on a surface pre-covered with an adsorbate, causing a reaction to occur between the surface and the adsorbate.  The reactions observed include dissociation, desorption, and absorption into the bulk of the substrate.  In addition, she discovered that

text: electron energy loss spectroscopy

text: can be used to detect species absorbed in the bulk of a substrate, and can be used to differentiate between bulk and surface species.  This paved the way for her discovery that hydrogen atoms absorbed in the bulk of a nickel sample are the key reactant in the hydrogenation of unsaturated hydrocarbons.  Another major discovery involved the reaction of fluorine molecules with a silicon surface (a reaction that is key to semiconductor device etching), in which the silicon surface abstracts a fluorine atom from the incident fluorine molecule, and the remaining fluorine atom scatters into the gas phase.  This is the reverse of the

text: Eley-Rideal

text: mechanism, one of the fundamental mechanism of gas-surface chemical reactions.

text: Physical organic chemistry, a term coined by Louis Hammett in 1940, refers to a discipline of organic chemistry that focuses on the relationship between chemical structures and reactivity, in particular, applying experimental tools of physical chemistry to the study of organic molecules. Specific focal points of study include the rates of organic reactions, the relative chemical stabilities of the starting materials, reactive intermediates, transition states, and products of chemical reactions, and non-covalent aspects of solvation and molecular interactions that influence chemical reactivity. Such studies provide theoretical and practical frameworks to understand how changes in structure in solution or solid-state contexts impact reaction mechanism and rate for each organic reaction of interest. Physical organic chemists use theoretical and experimental approaches work to understand these foundational problems in organic chemistry, including classical and statistical thermodynamic calculations, quantum mechanical theory and computational chemistry, as well as experimental spectroscopy (e.g., NMR), spectrometry (e.g., MS), and crystallography approaches. The field therefore has applications to a wide variety of more specialized fields, including electro- and photochemistry, polymer and supramolecular chemistry, and bioorganic chemistry, enzymology, and chemical biology, as well as to commercial enterprises involving process chemistry, chemical engineering, materials science and nanotechnology, and drug discovery.

text: Physical organic chemistry, a term coined by

text: Louis Hammett

text: in 1940, refers to a discipline of

text: organic chemistry

text: that focuses on the relationship between

text: chemical structure

text: s and

text: reactivity

text: , in particular, applying experimental tools of

text: physical chemistry

text: to the study of

text: organic molecules

text: . Specific focal points of study include the

text: rates

text: of

text: organic reactions

text: , the relative

text: chemical stabilities

text: of the starting materials,

text: reactive intermediate

text: s,

text: transition state

text: s, and products of

text: chemical reaction

text: s, and non-covalent aspects of

text: solvation

text: and

text: molecular interaction

text: s that influence chemical reactivity. Such studies provide theoretical and practical frameworks to understand how changes in structure in solution or solid-state contexts impact

text: reaction mechanism

text: and

text: rate

text: for each

text: organic reaction

text: of interest. Physical organic chemists use theoretical and experimental approaches work to understand these foundational problems in

text: organic chemistry

text: , including classical and statistical

text: thermodynamic

text: calculations,

text: quantum mechanical theory

text: and

text: computational chemistry

text: , as well as experimental

text: spectroscopy

text: (e.g.,

text: NMR

text: spectrometry

text: (e.g.,

text: MS

text: ), and

text: crystallography

text: approaches. The field therefore has applications to a wide variety of more specialized fields, including

text: electro-

text: and

text: photochemistry

text: polymer

text: and

text: supramolecular chemistry

text: , and

text: bioorganic chemistry

text: enzymology

text: , and

text: chemical biology

text: , as well as to commercial enterprises involving

text: process chemistry

text: chemical engineering

text: materials science

text: and

text: nanotechnology

text: , and

text: drug discovery

text: In organic chemistry, an electron donating group (EDG) or electron releasing group (ERG) is an atom or functional group that donates some of its electron density into a conjugated π system via resonance or inductive effects, thus making the π system more nucleophilic.  When attached to a benzene molecule, an electron donating group makes it more likely to participate in electrophilic substitution reactions. Benzene itself will normally undergo substitutions by electrophiles, but additional substituents can alter the reaction rate or products by electronically or sterically affecting the interaction of the two reactants. EDGs are often known as activating groups.

text: In

text: organic chemistry

text: , an electron donating group (EDG) or electron releasing group (ERG) is an atom or

text: functional group

text: that donates some of its

text: electron density

text: into a

text: conjugated π system

text: via

text: resonance

text: or

text: inductive effect

text: s, thus making the π system more

text: nucleophilic

text: .  When attached to a

text: benzene

text: molecule

text: , an electron donating group makes it more likely to participate in

text: electrophilic substitution reaction

text: s. Benzene itself will normally undergo

text: substitutions

text: by

text: electrophile

text: s, but additional

text: substituent

text: s can alter the

text: reaction rate

text: or

text: products

text: by

text: electronically

text: or

text: sterically

text: affecting the interaction of the two

text: reactant

text: s. EDGs are often known as activating groups.

text: The equilibrium concentration position of a reaction is said to lie "far to the right" if, at equilibrium, nearly all the reactants are consumed. Conversely the equilibrium position is said to be "far to the left" if hardly any product is formed from the reactants.

text: Because most deoxyribozymes suffer from product inhibition and thus exhibit single-turnover behavior, it is sometimes argued that deoxyribozymes do not exhibit "true" catalytic behavior since they cannot undergo multiple-turnover catalysis like most biological enzymes. However, the general definition of a catalyst requires only that the substance speeds up the rate of a chemical reaction without being consumed by the reaction (i.e. it is not permanently chemically altered and can be recycled). Thus, by this definition, single-turnover deoxyribozymes are indeed catalysts. Furthermore, many endogenous enzymes (both proteins and ribozymes) also exhibit single-turnover behavior, and so the exclusion of deoxyribozymes from the rank of "catalyst" simply because it does not feature multiple-turnover behavior seems unjustified.

text: Because most deoxyribozymes suffer from

text: product inhibition

text: and thus exhibit single-

text: turnover

text: behavior, it is sometimes argued that deoxyribozymes do not exhibit "true" catalytic behavior since they cannot undergo multiple-turnover catalysis like most biological

text: enzyme

text: s. However, the general definition of a

text: catalyst

text: requires only that the substance speeds up the

text: rate

text: of a

text: chemical reaction

text: without being consumed by the reaction (i.e. it is not permanently chemically altered and can be recycled). Thus, by this definition, single-turnover deoxyribozymes are indeed catalysts. Furthermore, many

text: endogenous

text: enzyme

text: s (both

text: protein

text: s and

text: ribozyme

text: s) also exhibit single-turnover behavior, and so the exclusion of deoxyribozymes from the rank of "catalyst" simply because it does not feature multiple-turnover behavior seems unjustified.

text: In chemical kinetics a reaction rate constant or reaction rate coefficient, k, quantifies the rate of a chemical reaction.

text: In

text: chemical kinetics

text: a reaction rate constant or reaction rate coefficient, k, quantifies the rate of a

text: chemical reaction

text: For faster reactions, the time required to mix the reactants and bring them to a specified temperature may be comparable or longer than the half-life of the reaction. Special methods to start fast reactions without slow mixing step include

text: For faster reactions, the time required to mix the reactants and bring them to a specified temperature may be comparable or longer than the

text: half-life

text: of the reaction. Special methods to start fast reactions without slow mixing step include

text: Catalysis () is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst ().  In most cases, reactions occur faster with a catalyst because they require less activation energy. Furthermore since they are not consumed in the catalyzed reaction, catalysts can continue to act repeatedly. Often only tiny amounts are required in principle.

text: Catalysis () is the increase in the

text: rate

text: of a

text: chemical reaction

text: due to the participation of an additional substance called a catalyst ().  In most cases, reactions occur faster with a catalyst because they require less

text: activation energy

text: . Furthermore since they are not consumed in the catalyzed reaction, catalysts can continue to act repeatedly. Often only tiny amounts are required in principle.

text: The number of physically-independent reactions can be even greater than the number of chemical components, and depends on the various reaction mechanisms. For example, there may be two (or more) reaction paths for the isomerism above. The reaction may occur by itself, but faster and with different intermediates, in the presence of a catalyst.

text: Nearly all chemical reactions can occur at normal temperatures (although different reactions proceed at different rates). However most reactions are accelerated by high temperatures, and the degradation of foods and pharmaceuticals is no exception. The same applies to the breakdown of many chemical explosives into more unstable compounds. Nitroglycerine is notorious. Old explosives are thus more dangerous (i.e. liable to be triggered to explode by very small disturbances, even trivial jiggling) than more recently manufactured explosives. Rubber products also degrade as sulphur bonds induced during vulcanization revert; this is why old rubber bands and other rubber products soften and get crispy, and lose their elasticity as they age.

text: Nearly all chemical reactions can occur at normal temperatures (although different reactions proceed at different rates). However most reactions are accelerated by high temperatures, and the degradation of foods and pharmaceuticals is no exception. The same applies to the breakdown of many chemical explosives into more unstable compounds.

text: Nitroglycerin

text: e is notorious. Old

text: explosives

text: are thus more dangerous (i.e. liable to be triggered to explode by very small disturbances, even trivial jiggling) than more recently manufactured explosives.

text: Rubber

text: products also degrade as

text: sulphur

text: bonds

text: induced during

text: vulcanization

text: revert; this is why old

text: rubber band

text: s and other rubber products soften and get crispy, and lose their elasticity as they age.

text: For example, in an aqueous buffer solution the reaction rate for reactants R depends on the pH of the system but not on the concentrations of different acids.

text: For example, in an aqueous

text: buffer solution

text: the reaction rate for reactants R depends on the

text: pH

text: of the system but not on the

text: concentration

text: s of different acids.

text: In physical organic chemistry, a free-energy relationship or Gibbs energy relation  relates the logarithm of a reaction rate constant or equilibrium constant for one series of reactions with the logarithm of the rate or equilibrium constant for a related series of reactions. Establishing free-energy relationships helps in the understanding of the reaction mechanism for a chemical reaction and allows the prediction of reaction rates and equilibrium constants.

text: In

text: physical organic chemistry

text: , a free-energy relationship or Gibbs energy relation  relates the

text: logarithm

text: of a

text: reaction rate constant

text: or

text: equilibrium constant

text: for one series of reactions with the logarithm of the rate or equilibrium constant for a related series of reactions. Establishing free-energy relationships helps in the understanding of the

text: reaction mechanism

text: for a

text: chemical reaction

text: and allows the prediction of reaction rates and equilibrium constants.

text: The storage condition of the bottled wine will influence a wine's aging. Vibrations and heat fluctuations can hasten a wine's deterioration and cause adverse effect on the wines. In general, a wine has a greater potential to develop complexity and more aromatic bouquet if it is allowed to age slowly in a relatively cool environment. The lower the temperature, the more slowly a wine develops. On average, the rate of chemical reactions in wine double with each 18 °F (8 °C) increase in temperature. Wine expert Karen MacNeil, recommends keeping wine intended for aging in a cool area with a constant temperature around 55 °F (13 °C). Wine can be stored at temperatures as high as 69 °F (20 °C) without long term negative effect. Professor Cornelius Ough of the University of California, Davis believes that wine could be exposed to temperatures as high as 120 °F (49 °C) for a few hours and not be damaged. However, most experts believe that extreme temperature fluctuations (such as repeated transferring a wine from a warm room to a cool refrigerator) would be detrimental to the wine. The ultra-violet rays of direct sunlight should also be avoided because of the free radicals that can develop in the wine and result in premature oxidation.

text: The storage condition of the bottled wine will influence a wine's aging. Vibrations and heat fluctuations can hasten a wine's deterioration and cause adverse effect on the wines. In general, a wine has a greater potential to develop complexity and more aromatic bouquet if it is allowed to age slowly in a relatively cool environment. The lower the temperature, the more slowly a wine develops. On average, the rate of chemical reactions in wine double with each 18 °F (8 °C) increase in temperature. Wine expert

text: Karen MacNeil

text: , recommends keeping wine intended for aging in a cool area with a constant temperature around 55 °F (13 °C). Wine can be stored at temperatures as high as 69 °F (20 °C) without long term negative effect. Professor Cornelius Ough of the

text: University of California, Davis

text: believes that wine could be exposed to temperatures as high as 120 °F (49 °C) for a few hours and not be damaged. However, most experts believe that extreme temperature fluctuations (such as repeated transferring a wine from a warm room to a cool refrigerator) would be detrimental to the wine. The

text: ultra-violet

text: rays of direct sunlight should also be avoided because of the

text: free radicals

text: that can develop in the wine and result in

text: premature oxidation

text: The same is true, up to a point, of the chemical reactions of living things. They are usually catalyzed by enzymes which change reaction rates, but with no variation in catalytic action, the rule of thumb is still mostly applicable. In the case of bacteria and fungi, the reactions needed to feed and reproduce speed up at higher temperatures, up to the point that the proteins and other compounds in their cells themselves begin to break down, or denature, so quickly that they cannot be replaced. This is why high temperatures kill bacteria and other micro-organisms: 'tissue' breakdown reactions reach such rates that they cannot be compensated for and the cell dies. On the other hand, 'elevated' temperatures short of these result in increased growth and reproduction; if the organism is harmful, perhaps to dangerous levels.

text: The same is true, up to a point, of the chemical reactions of living things. They are usually catalyzed by

text: enzyme

text: s which change reaction rates, but with no variation in catalytic action, the rule of thumb is still mostly applicable. In the case of

text: bacteria

text: and

text: fungi

text: , the reactions needed to feed and reproduce speed up at higher temperatures, up to the point that the proteins and other compounds in their cells themselves begin to break down, or

text: denature

text: , so quickly that they cannot be replaced. This is why high temperatures kill bacteria and other micro-organisms: 'tissue' breakdown reactions reach such rates that they cannot be compensated for and the cell dies. On the other hand, 'elevated' temperatures short of these result in increased growth and reproduction; if the organism is harmful, perhaps to dangerous levels.

text: Many intermediates are short-lived and highly reactive, thus having a low concentration in the reaction mixture. As is always the case when discussing chemical kinetics, definitions like fast/slow short/long-lived are relative, and depend on the relative rates of all the reactions involved. Species that are short-lived in one reaction mechanism, can be considered stable in others and molecular entities that are intermediates in some mechanisms can be stable enough to be detected, identified, isolated or used as reactants in (or be the products of) other reactions. Reaction intermediates are often free radicals or unstable ions. Oxidizing radicals (OOH and OH) found in combustion reactions are so reactive that a high temperature is required to constantly produce them, in order to compensate their disappearance, or the combustion reaction will cease.

text: Many intermediates are short-lived and highly reactive, thus having a low concentration in the reaction mixture. As is always the case when discussing

text: chemical kinetics

text: , definitions like fast/slow short/long-lived are relative, and depend on the relative

text: rates

text: of all the reactions involved. Species that are short-lived in one

text: reaction mechanism

text: , can be considered stable in others and molecular entities that are intermediates in some mechanisms can be stable enough to be

text: detected

text: identified

text: , isolated or used as reactants in (or be the products of) other reactions. Reaction intermediates are often

text: free radical

text: s or unstable ions. Oxidizing radicals (OOH and OH) found in combustion reactions are so reactive that a high temperature is required to constantly produce them, in order to compensate their disappearance, or the combustion reaction will cease.

text: Bases can be thought of as the chemical opposite of acids. However, some strong acids are able to act as bases. Bases and acids are seen as opposites because the effect of an acid is to increase the hydroxonium (HO) concentration in water, whereas bases reduce this concentration. A reaction between an acid and base is called neutralization. In a neutralization reaction, an aqueous solution of a base reacts with an aqueous solution of an acid to produce a solution of water and salt in which the salt separates into its component ions. If the aqueous solution is saturated with a given salt solute, any additional such salt precipitates out of the solution.

text: Bases can be thought of as the chemical opposite of

text: acid

text: s. However, some strong acids are able to act as bases. Bases and acids are seen as opposites because the effect of an acid is to increase the

text: hydroxonium

text: (HO) concentration in water, whereas bases reduce this concentration. A reaction between an acid and base is called

text: neutralization

text: . In a neutralization reaction, an aqueous solution of a base reacts with an aqueous solution of an acid to produce a solution of

text: water

text: and

text: salt

text: in which the salt separates into its component ions. If the aqueous solution is

text: saturated

text: with a given salt

text: solute

text: , any additional such salt

text: precipitate

text: s out of the solution.

text: When looking at chemical surfaces, many researchers seems to agree on that the surface of the Cu/AlO/ZnO is most similar to the Cu(111) surface.  Since copper is the main catalyst and the active phase in the LTS catalyst, many experiments has been done with copper. In the figure given here experiments has been done on Cu(110) and Cu(111). The figure shows Arrhenius plot derived from reaction rates. It can be seen from the figure that Cu(110) shows a faster reaction rate and a lower activation energy. This can be due to the fact that Cu(111) is more closely packed than Cu(110).

text: Chemical systems cannot oscillate about a position of final equilibrium because such an oscillation would violate the second law of thermodynamics. For a thermodynamic system which is not at equilibrium, this law requires that the system approach equilibrium and not recede from it. For a closed system at constant temperature and pressure, the thermodynamic requirement is that the Gibbs free energy must decrease continuously and not oscillate. However it is possible that the concentrations of some reaction intermediates oscillate, and also that the rate of formation of products oscillates.

text: Chemical systems cannot oscillate about a position of final

text: equilibrium

text: because such an oscillation would violate the

text: second law of thermodynamics

text: . For a

text: thermodynamic system

text: which is not at equilibrium, this law requires that the system approach equilibrium and not recede from it. For a closed system at constant temperature and pressure, the thermodynamic requirement is that the

text: Gibbs free energy

text: must decrease continuously and not oscillate. However it is possible that the concentrations of some

text: reaction intermediate

text: s oscillate, and also that the rate of formation of products oscillates.

text: Another set of important questions in chemistry concerns what kind of reactions can happen spontaneously and which properties are possible for a given chemical mixture. This is studied in chemical thermodynamics, which sets limits on quantities like how far a reaction can proceed, or how much energy can be converted into work in an internal combustion engine, and which provides links between properties like the thermal expansion coefficient and rate of change of entropy with pressure for a gas or a liquid. It can frequently be used to assess whether a reactor or engine design is feasible, or to check the validity of experimental data. To a limited extent, quasi-equilibrium and non-equilibrium thermodynamics can describe irreversible changes. However, classical thermodynamics is mostly concerned with systems in equilibrium and reversible changes and not what actually does happen, or how fast, away from equilibrium.

text: Another set of important questions in chemistry concerns what kind of reactions can happen spontaneously and which properties are possible for a given chemical mixture. This is studied in

text: chemical thermodynamics

text: , which sets limits on quantities like how far a reaction can proceed, or how much energy can be converted into work in an

text: internal combustion engine

text: , and which provides links between properties like the

text: thermal expansion coefficient

text: and rate of change of

text: entropy

text: with

text: pressure

text: for a

text: gas

text: or a

text: liquid

text: . It can frequently be used to assess whether a reactor or engine design is feasible, or to check the validity of experimental data. To a limited extent,

text: quasi-equilibrium

text: and

text: non-equilibrium thermodynamics

text: can describe irreversible changes. However, classical thermodynamics is mostly concerned with systems in

text: equilibrium

text: and

text: reversible changes

text: and not what actually does happen, or how fast, away from equilibrium.

text: Since the oxidation of aluminum is exothermic, these reactions can operate under mild temperatures and pressures, providing a stable and compact source of hydrogen. This chemical reduction process is specially suitable for back-up, remote or marine applications.  While the passivation of aluminum would normally slow this reaction considerably, its negative effects can be minimized by changing several experimental parameters such as temperature, alkali concentration, physical form of the aluminum, and solution composition.

text: Since the oxidation of aluminum is exothermic, these reactions can operate under mild temperatures and pressures, providing a stable and compact source of hydrogen. This

text: chemical reduction

text: process is specially suitable for back-up, remote or marine applications.  While the

text: passivation

text: of aluminum would normally slow this reaction considerably, its negative effects can be minimized by changing several experimental parameters such as temperature, alkali concentration, physical form of the aluminum, and solution composition.

text: It was furthermore found that the rate of the reaction depends on the concentration of the hydroxylic solvent and on the cation in the alkoxide catalyst. The presence of crown ether in the reaction medium can increase the reactivity of the hydrazone anion 1 by dissociating the ion pair and therefore enhance the reaction rate. The final step of the Wolff–Kishner reduction is the collapse of the diimide anion 2 in the presence of a proton source to give the hydrocarbon via loss of dinitrogen. Taber showed experimental evidence for the intermediacy of a sp-hybridized carbanion 3 during this last step, distinguishing it from a mechanism in which dinitrogen is lost by a free-radical pathway. The overall driving force of the reaction is the evolution of nitrogen gas from the reaction mixture.

text: It was furthermore found that the rate of the reaction depends on the concentration of the hydroxylic solvent and on the cation in the alkoxide catalyst. The presence of

text: crown ether

text: in the reaction medium can increase the reactivity of the hydrazone anion 1 by dissociating the ion pair and therefore enhance the reaction rate. The final step of the Wolff–Kishner reduction is the collapse of the diimide anion 2 in the presence of a proton source to give the hydrocarbon via loss of dinitrogen. Taber showed experimental evidence for the intermediacy of a sp-hybridized

text: carbanion

text: 3 during this last step, distinguishing it from a mechanism in which dinitrogen is lost by a free-radical pathway. The overall driving force of the reaction is the evolution of nitrogen gas from the reaction mixture.

text: The sum of the molecular masses of the reactants is 642.6 g/mol, so theoretically a cell can produce two faradays of charge (192,971 coulombs) from 642.6 g of reactants, or 83.4 ampere-hours per kilogram (or 13.9 ampere-hours per kilogram for a 12-volt battery). For a 2 volts cell, this comes to 167 watt-hours per kilogram of reactants, but a lead–acid cell in practice gives only 30–40 watt-hours per kilogram of battery, due to the mass of the water and other constituent parts.

text: The sum of the molecular masses of the reactants is 642.6 g/mol, so theoretically a cell can produce two

text: faradays

text: of charge (192,971

text: coulomb

text: s) from 642.6 g of reactants, or 83.4

text: ampere-hour

text: s per kilogram (or 13.9 ampere-hours per kilogram for a 12-volt battery). For a 2 volts cell, this comes to 167

text: watt-hour

text: s per kilogram of reactants, but a lead–acid cell in practice gives only 30–40 watt-hours per kilogram of battery, due to the mass of the water and other constituent parts.

text: Chemical absorption or reactive absorption is a chemical reaction between the absorbed and the absorbing substances. Sometimes it combines with physical absorption. This type of absorption depends upon the stoichiometry of the reaction and the concentration of its reactants.

text: Chemical absorption or reactive absorption is a chemical reaction between the absorbed and the absorbing substances. Sometimes it combines with physical absorption. This type of absorption depends upon the

text: stoichiometry

text: of the reaction and the concentration of its reactants.

text: Different chemical reactions are used in combinations during chemical synthesis in order to obtain a desired product. In biochemistry, a consecutive series of chemical reactions (where the product of one reaction is the reactant of the next reaction) form metabolic pathways. These reactions are often catalyzed by protein enzymes. Enzymes increase the rates of biochemical reactions, so that metabolic syntheses and decompositions impossible under ordinary conditions can occur at the temperatures and concentrations present within a cell.

text: Different chemical reactions are used in combinations during

text: chemical synthesis

text: in order to obtain a desired product. In

text: biochemistry

text: , a consecutive series of chemical reactions (where the product of one reaction is the reactant of the next reaction) form

text: metabolic pathway

text: s. These reactions are often

text: catalyzed

text: by protein

text: enzyme

text: s. Enzymes increase the rates of biochemical reactions, so that

text: metabolic

text: syntheses and decompositions impossible under ordinary conditions can occur at the temperatures and concentrations present within a

text: cell

text: In chemistry, reaction progress kinetic analysis (RPKA) is a subset of a broad range of kinetic techniques utilized to determine the rate laws of chemical reactions and to aid in elucidation of reaction mechanisms. While the concepts guiding reaction progress kinetic analysis are not new, the process was formalized by Professor Donna Blackmond (currently at Scripps Research Institute) in the late 1990s and has since seen increasingly widespread use. Unlike more common pseudo-first-order analysis, in which an overwhelming excess of one or more reagents is used relative to a species of interest, RPKA probes reactions at synthetically relevant conditions (i.e. with concentrations and reagent ratios resembling those used in the reaction when not exploring the rate law.) Generally, this analysis involves a system in which the concentrations of multiple reactants are changing measurably over the course of the reaction. As the mechanism can vary depending on the relative and absolute concentrations of the species involved, this approach obtains results that are much more representative of reaction behavior under commonly utilized conditions than do traditional tactics. Furthermore, information obtained by observation of the reaction over time may provide insight regarding unexpected behavior such as induction periods, catalyst deactivation, or changes in mechanism.

text: In

text: chemistry

text: , reaction progress kinetic analysis (RPKA) is a subset of a broad range of

text: kinetic

text: techniques utilized to determine the

text: rate law

text: s of chemical reactions and to aid in elucidation of

text: reaction mechanism

text: s. While the concepts guiding reaction progress kinetic analysis are not new, the process was formalized by Professor

text: Donna Blackmond

text: (currently at

text: Scripps Research Institute

text: ) in the late 1990s and has since seen increasingly widespread use. Unlike more common

text: pseudo-first-order

text: analysis, in which an overwhelming excess of one or more reagents is used relative to a species of interest, RPKA probes reactions at synthetically relevant conditions (i.e. with concentrations and reagent ratios resembling those used in the reaction when not exploring the rate law.) Generally, this analysis involves a system in which the concentrations of multiple reactants are changing measurably over the course of the reaction. As the

text: mechanism

text: can vary depending on the relative and absolute

text: concentration

text: s of the species involved, this approach obtains results that are much more representative of reaction behavior under commonly utilized conditions than do traditional tactics. Furthermore, information obtained by observation of the reaction over time may provide insight regarding unexpected behavior such as induction periods, catalyst deactivation, or changes in mechanism.

text: Note that the free reactant concentrations can be regarded as implicit parameters in the equilibrium constant refinement process. In that context the values of the free concentrations are constrained by forcing the conditions of mass-balance to apply at all stages of the process.

text: The flow of reactants into the reaction chamber and subsequent ejection occur in a series of about 70 pulses, at a rate of about 500 pulses per second. The whole sequence of events takes only a fraction of a second. These pulsations are caused by repeated microexplosions which are the results of the continuous pressure on the reservoir and the oscillatory opening and closing of the valve that controls access to the reaction chamber. This pulsed mechanism is beneficial for the beetles' survival because the system uses pressure instead of muscles to eject the spray at a constant velocity, saving the beetle energy. Also, the reintroduction of new reactants into the vestibule where enzymes are stored, reduces the temperature of the chamber, thereby protecting the peroxidases and catalases from thermal denaturation.

text: In chemical kinetics, the overall reaction rate is often explained using a mechanism consisting of a number of elementary steps. Not all of these steps affect the rate of reaction; normally the slowest elementary step controls the reaction rate. For this example, a possible mechanism is:

text: So, when a reaction has a rate constant that obeys Arrhenius' equation, a plot of ln(k) versus T gives a straight line, whose gradient and intercept can be used to determine E and A . This procedure has become so common in experimental chemical kinetics that practitioners have taken to using it to define the activation energy for a reaction. That is the activation energy is defined to be (−R) times the slope of a plot of ln(k) vs. (1/T )

text: C       = Concentration of reactant A

text: C       = Concentration of reactant A

text: Inhibition should be distinguished from catalyst poisoning. An inhibitor only hinders the working of a catalyst without changing it, whilst in catalyst poisoning the catalyst undergoes a chemical reaction that is irreversible in the environment in question (the active catalyst may only be regained by a separate process

text: Metabolic flux refers to the rate of metabolite conversion in a metabolic network.  For a reaction this rate is a function of both enzyme abundance and enzyme activity.  Enzyme concentration is itself a function of transcriptional and translational regulation in addition to the stability of the protein.  Enzyme activity is affected by the kinetic parameters of the enzyme, the substrate concentrations, the product concentrations, and the effector molecules concentration.  The genomic and environmental effects on metabolic flux are what determine healthy or diseased phenotype.

text: Expressed in a chemical equation:  reactants → products + energy

text: Expressed in a

text: chemical equation

text: :  reactants → products + energy

text: The human sense of smell is a primary factor in the sensation of comfort. Olfaction as a sensory system brings awareness of the presence of airborne chemicals. Some inhaled chemicals are volatile compounds that act as a stimulus, triggering unwanted reactions such as nose, eye, and throat irritation. Perception of odor and of irritation is unique to each person, and varies because of physical conditions or memory of past exposures to similar chemicals. A person's specific threshold before an odor becomes a nuisance depends also on the frequency, concentration, and duration of an odor.

text: The human sense of smell is a primary factor in the sensation of comfort. Olfaction as a sensory system brings awareness of the presence of airborne chemicals. Some inhaled chemicals are volatile compounds that act as a stimulus, triggering unwanted reactions such as nose, eye, and

text: throat irritation

text: . Perception of odor and of irritation is unique to each person, and varies because of physical conditions or memory of past exposures to similar chemicals. A person's specific threshold before an odor becomes a nuisance depends also on the frequency, concentration, and duration of an odor.

text: Primary condition is addition of reactant molecules at a very small rate to SWNT solution for a sufficient long time. This ensures reaction with only metallic SWNTs and with no semiconducting SWNTs as all the reactant molecules are taken up by the metallic SWNTs. Long time injection ensures that all metallic tubes are reacted. For example, one highly selective condition is: addition of 500 µL of 4-hydroxybenzene diazonium tetrafluoroborate solution in water (0.245 mM) at an injection rate of 20.83 µL/h into 5 mL of SWNT solution (1 wt % sodium dodecyl sulfate (SDS)) over 24 hrs. However, if the entire diazonium solution is added all instantaneously then semiconducting SWNTs will also react due to presence of excess reactant.

text: Primary condition is addition of reactant molecules at a very small rate to SWNT solution for a sufficient long time. This ensures reaction with only metallic SWNTs and with no semiconducting SWNTs as all the reactant molecules are taken up by the metallic SWNTs. Long time injection ensures that all metallic tubes are reacted. For example, one highly selective condition is: addition of 500 µL of 4-hydroxybenzene diazonium tetrafluoroborate solution in water (0.245 mM) at an injection rate of 20.83 µL/h into 5 mL of SWNT solution (1 wt %

text: sodium dodecyl sulfate

text: (SDS)) over 24 hrs. However, if the entire diazonium solution is added all instantaneously then semiconducting SWNTs will also react due to presence of excess reactant.

text: Applying the law of mass action, which states that the rate of a reaction is proportional to the product of the concentrations of the reactants (i.e.[E][S]), gives a system of four non-linear ordinary differential equations that define the rate of change of reactants with time

text: Applying the

text: law of mass action

text: , which states that the rate of a reaction is proportional to the product of the concentrations of the reactants (i.e.[E][S]), gives a system of four non-linear

text: ordinary differential equation

text: s that define the rate of change of reactants with time

text: Do not forget that the stoichiometric number of reactants is negative. Now when we know the extent, we can rearrange the equation and calculate the equilibrium amounts of B and C.

text: These catalysts often tend towards deactivation and display poor reusability qualities. This has been attributed to a variety of causes including: metal oxidation, metal loss due to leaching or sintering, or a decrease in surface area as a result of pore occlusion. The occurrences of metal leaching and oxidation are observed far less often in catalysts composedof palladium. The cause of catalyst poisoning can generally be attributed to the CO that forms in the duration of a deCOx reaction or due to sulfur or phosphorusimpurities in the reaction feeds. An additional cause of deactivation may occur as a result of aromatic compounds adsorbing to the catalysts; these compounds being found in the feeds or produced during the course of a reaction. However, the primary cause of catalyst deactivation can be ascribed to surface area loss due to pore occlusion from deposits on the catalyst surface.

text: These catalysts often tend towards deactivation and display poor reusability qualities. This has been attributed to a variety of causes including: metal oxidation, metal loss due to leaching or sintering, or a decrease in surface area as a result of pore occlusion. The occurrences of metal leaching and oxidation are observed far less often in catalysts composedof palladium. The cause of catalyst poisoning can generally be attributed to the CO that forms in the duration of a deCOx reaction or due to

text: sulfur

text: or

text: phosphorus

text: impurities in the reaction feeds. An additional cause of deactivation may occur as a result of aromatic compounds adsorbing to the catalysts; these compounds being found in the feeds or produced during the course of a reaction. However, the primary cause of catalyst deactivation can be ascribed to surface area loss due to pore occlusion from deposits on the catalyst surface.

text: Here k is first-order rate constant having dimension 1/time, [A](t) is concentration at a time t and [A] is the initial concentration. The rate of a first-order reaction depends only on the concentration and the properties of the involved substance, and the reaction itself can be described with the characteristic half-life. More than one time constant is needed when describing reactions of higher order. The temperature dependence of the rate constant usually follows the Arrhenius equation:

text: Here k is first-order rate constant having dimension 1/time, [A](t) is concentration at a time t and [A] is the initial concentration. The rate of a first-order reaction depends only on the concentration and the properties of the involved substance, and the reaction itself can be described with the characteristic

text: half-life

text: . More than one time constant is needed when describing reactions of higher order. The temperature dependence of the rate constant usually follows the

text: Arrhenius equation

text: Orthodox chemical rockets use heat energy produced by chemical reactions in a reaction chamber to heat the gas products. The products are then expelled through a propulsion nozzle at a very high speed, creating thrust. In a nuclear thermal rocket (NTR), thrust is created by heating a fluid by using a nuclear fission reactor. The lower the molecular weight of the exhaust, hydrogen in the best case, the more efficient the motor can be. However, in this engine the propellant can be anything with suitable properties as there will be no reaction on the part of the propellant. In an NSWR the nuclear salt-water would be made to flow through a reaction chamber and out an exhaust nozzle in such a way and at such speeds that critical mass will begin once at the chamber is filled to a certain point, however, the peak neutron flux in the fission reaction would occur outside the vehicle.

text: Orthodox

text: chemical rocket

text: s use heat energy produced by chemical reactions in a reaction chamber to heat the gas products. The products are then expelled through a propulsion nozzle at a very high speed, creating thrust. In a

text: nuclear thermal rocket

text: (NTR), thrust is created by heating a fluid by using a nuclear fission reactor. The lower the

text: molecular weight

text: of the exhaust, hydrogen in the best case, the more efficient the motor can be. However, in this engine the propellant can be anything with suitable properties as there will be no reaction on the part of the propellant. In an NSWR the nuclear salt-water would be made to flow through a reaction chamber and out an exhaust nozzle in such a way and at such speeds that critical mass will begin once at the chamber is filled to a certain point, however, the peak

text: neutron flux

text: in the

text: fission

text: reaction would occur outside the vehicle.

text: Taking an example from the food processing industry: fluidized beds are used to accelerate freezing in some IQF tunnel freezers (IQF means Individually Quick Frozen, or freezing unpackaged separate pieces). These fluidized bed tunnels are typically used on small food products like peas, shrimp or sliced vegetables, and may use cryogenic or vapor-compression refrigeration. The fluid used in fluidized beds may also contain a fluid of catalytic type; that's why it is also used to catalyse the chemical reaction and also to improve the rate of reaction.

text: Taking an example from the food processing industry: fluidized beds are used to accelerate freezing in some

text: IQF tunnel freezers

text: (IQF means Individually Quick Frozen, or freezing unpackaged separate pieces). These fluidized bed tunnels are typically used on small food products like peas, shrimp or sliced vegetables, and may use

text: cryogenic

text: or

text: vapor-compression refrigeration

text: . The fluid used in fluidized beds may also contain a fluid of catalytic type; that's why it is also used to catalyse the chemical reaction and also to improve the rate of reaction.

text: Catalyst interactions with multiple components of a reaction mixture can lead to a complex kinetic dependence. While off-cycle catalyst-substrate or catalyst-product interactions are generally considered "poisonous" to the system (certainly the case in the event of irreversible complexation) cases do exist in which the off-cycle species actually protects the catalyst from permanent deactivation.In either case, it is often essential to understand the role of the catalyst resting state.

text: Although a specialized application, SnCl is used in Friedel-Crafts reactions as a Lewis acidic catalyst for alkylation and cyclisation.  Stannic chloride is used in chemical reactions with fuming (90%) nitric acid for the selective nitration of activated aromatic rings in the presence of inactivated ones.

text: Although a specialized application, SnCl is used in

text: Friedel-Crafts reaction

text: s as a Lewis acidic

text: catalyst

text: for alkylation and cyclisation.  Stannic chloride is used in chemical reactions with fuming (90%) nitric acid for the selective nitration of activated aromatic rings in the presence of inactivated ones.

text: According to IUPAC's Gold Book definitionthe reaction rate r for a chemical reaction occurring in a closed system under isochoric conditions, without a build-up of reaction intermediates, is defined as:

text: According to

text: IUPAC

text: 's

text: Gold Book

text: definitionthe reaction rate r for a chemical reaction occurring in a

text: closed system

text: under

text: isochoric conditions

text: , without a build-up of

text: reaction intermediate

text: s, is defined as:

text: Like S2 reactions, there are quite a few factors that affect the reaction rate of S1 reactions.  Instead of having two concentrations that affect the reaction rate, there is only one, substrate.  The rate equation for this would be Rate=k[Sub].  Since the rate of a reaction is only determined by its slowest step, the rate at which the leaving group "leaves" determines the speed of the reaction.  This means that the better the leaving group, the faster the reaction rate.  A general rule for what makes a good leaving group is the weaker the conjugate base, the better the leaving group.  In this case, halogens are going to be the best leaving groups, while compounds such as amines, hydrogen, and alkanes are going to be quite poor leaving groups.  As S2 reactions were affected by sterics, S1 reactions are determined by bulky groups attached to the carbocation.  Since there is an intermediate that actually contains a positive charge, bulky groups attached are going to help stabilize the charge on the carbocation through resonance and distribution of charge.  In this case, tertiary carbocation will react faster than a secondary which will react much faster than a primary.  It is also due to this carbocation intermediate that the product does not have to have inversion.  The nucleophile can attack from the top or the bottom and therefore create a racemic product.  It is important to use a protic solvent, water and alcohols, since an aprotic solvent could attack the intermediate and cause unwanted product.  It does not matter if the hydrogens from the protic solvent react with the nucleophile since the nucleophile is not involved in the rate determining step.

text: Here, we have neglected the depletion of the reactant A, since its concentration is so large. The rate constants for the three reactions are

text: The term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances.

text: The term

text: chemical energy

text: is often used to indicate the potential of a chemical substance to undergo a transformation through a

text: chemical reaction

text: or to transform other chemical substances.

text: These results relate to whether a chemical reaction network can produce significantly different behaviour depending on the initial concentrations of its constituent reactants. This has applications in e.g. modelling biological switches — a high concentration of a key chemical at steady state could represent a biological process being "switched on" whereas a low concentration would represent being "switched off".

text: These results relate to whether a chemical reaction network can produce significantly different behaviour depending on the initial concentrations of its constituent reactants. This has applications in e.g. modelling

text: biological

text: switches — a high concentration of a key chemical at steady state could represent a biological process being "switched on" whereas a low concentration would represent being "switched off".

text: Raman spectroscopy is one of the methods easiest to integrate into a heterogeneous operando experiment, as these reactions typically occur in the gas phase, so there is very low litter interference and good data can be obtained for the species on the catalytic surface.  In order to use Raman, all that is required is to insert a small probe containing two optical fibers for excitation and detection. Pressure and heat complications are essentially negligible, due to the nature of the probe. Operando confocal Raman micro-spectroscopy has been applied to the study of fuel cell catalytic layers with flowing reactant streams and controlled temperature.<ref name= "Smotkin"

text: , abscissa). Arrhenius plots are often used to analyze the effect of temperature on the rates of chemical reactions. For a single rate-limited thermally activated process, an Arrhenius plot gives a straight line, from which the activation energy and the pre-exponential factor can both be determined.

text: abscissa

text: ). Arrhenius plots are often used to analyze the effect of temperature on the rates of chemical reactions. For a single rate-limited thermally activated process, an Arrhenius plot gives a straight line, from which the

text: activation energy

text: and the

text: pre-exponential factor

text: can both be determined.

text: An eventual step is selection of compounds that are known as reagents or reactants. Various reaction types can be applied to these to synthesize the product, or an intermediate product. This requires mixing the compounds in a reaction vessel such as a chemical reactor or a simple round-bottom flask.  Many reactions require some form of work-up procedure before the final product is isolated. The isolation (purification) of the product then proceeds via a variety of methods.

text: An eventual step is selection of

text: compounds

text: that are known as

text: reagent

text: s or reactants.

text: Various reaction types

text: can be applied to these to synthesize the product, or an intermediate product. This requires mixing the compounds in a reaction vessel such as a

text: chemical reactor

text: or a simple

text: round-bottom flask

text: .  Many reactions require some form of

text: work-up

text: procedure before the final product is isolated. The isolation (purification) of the product then proceeds via a variety of methods.

text: where A is the reactant and S is an adsorption site on the surface and the respective rate constants for the adsorption, desorption and reaction are k, k and k, then the global reaction rate is:

text: where A is the reactant and S is an adsorption site on the surface and the respective

text: rate constant

text: s for the adsorption, desorption and reaction are k, k and k, then the global reaction rate is:

text: One O-independent process involves a direct chemical reaction of Fe (commonly present in typical igneous minerals) or metallic Fe with HO to produce Fe(aq), which typically leads to hydroxides such as goethite (FeO•OH) under experimental conditions. While this reaction with HO is thermodynamically disfavored, it may be sustained nevertheless, by the rapid loss of the H byproduct. The reaction can be further facilitated by dissolved CO and SO, which lower the pH of brine films increasing the concentration of the more oxidative H.

text: If one reaction occurs much faster than the other one (k > k), it (k) will be called the main reaction, the other one (k) side reaction. If both reactions roughly of same speed (k ≅ k) is spoken of parallel reactions.

text: A reaction calorimeter is a calorimeter in which a chemical reaction is initiated within a closed insulated container. Reaction heats are measured and the total heat is obtained by integrating heatflow versus time. This is the standard used in industry to measure heats since industrial processes are engineered to run at constant temperatures. Reaction calorimetry can also be used to determine maximum heat release rate for chemical process engineering and for tracking the global kinetics of reactions. There are four main methods for measuring the heat in reaction calorimeter:

text: A reaction calorimeter is a calorimeter in which a

text: chemical reaction

text: is initiated within a closed insulated container. Reaction heats are measured and the total heat is obtained by integrating heatflow versus time. This is the standard used in industry to measure heats since industrial processes are engineered to run at constant temperatures. Reaction calorimetry can also be used to determine maximum heat release rate for chemical process engineering and for tracking the global kinetics of reactions. There are four main methods for measuring the heat in reaction calorimeter:

text: Reactions on surfaces are reactions in which at least one of the steps of the reaction mechanism is the adsorption of one or more reactants. The mechanisms for these reactions, and the rate equations are of extreme importance for heterogeneous catalysis. Via scanning tunneling microscopy, it is possible to observe reactions at the solid|gas interface in real space, if the time scale of the reaction is in the correct range. Reactions at the solid|gas interface are in some cases related to catalysis.

text: Reactions on surfaces are reactions in which at least one of the steps of the

text: reaction mechanism

text: is the

text: adsorption

text: of one or more reactants. The mechanisms for these reactions, and the

text: rate equation

text: s are of extreme importance for

text: heterogeneous catalysis

text: . Via

text: scanning tunneling microscopy

text: , it is possible to observe reactions at the solid|gas interface in real space, if the time scale of the reaction is in the correct range. Reactions at the solid|gas interface are in some cases related to catalysis.

text: . As an example of the first type, the reaction NO + CO → NO + CO is second-order in the reactant NO and zero order in the reactant CO. The observed rate is given by <math chem> r= k [\ce{NO2}]^2\, </math>, and is independent of the concentration of CO.

text: The product-determining step is the step of a chemical reaction that determines the ratio of products formed via differing reaction mechanisms that start from the same reactants. The product determining step is not rate limiting if the rate limiting step of each mechanism is the same.

text: The product-determining step is the step of a

text: chemical reaction

text: that determines the ratio of

text: products

text: formed via differing

text: reaction mechanism

text: s that start from the same

text: reactant

text: s. The product determining step is not rate limiting if the

text: rate limiting step

text: of each mechanism is the same.

text: Gustav Kirchhoff showed in 1858 that the variation of the heat of reaction is given by the difference in heat capacity between products and reactants: dΔH / dT = ΔC. Integration of this equation permits the evaluation of the heat of reaction at one temperature from measurements at another temperature.

text: Gustav Kirchhoff

text: showed in 1858 that the variation of the heat of reaction is given by the difference in

text: heat capacity

text: between products and reactants: dΔH / dT = ΔC. Integration of this equation permits the evaluation of the heat of reaction at one temperature from measurements at another temperature.

text: In comparison to RhCl(PHCy), the iridium analogue has reduced catalytic activity on the dehydrogenation of non sterically hindered amine-boranes, and increased activity on more sterically hindered substrates. Dehydrocoupling of primary diborazanes NHR—BH—NHR—BH can be catalyzed by Brookhart's catalyst via conversion to the metal-bound species MeNH—BH and subsequent polymerization/oligomerization. This same reaction has been found to occur in the absence of the iridium metal, upon heating of the reaction mixture. Dehydrogenation of ammonia-borane with Brookhart's catalyst results in quantitative formation of the cyclic pentamer [NHBH] rather than the typically seen cyclic dimers from other amine-borane dehydrogenations. When catalyzing ammonia-borane dehydrogenation, the catalyst acts homogeneously at a 0.5 mol% catalyst loading. Rather than the typical high temperatures needed for this dehydrogenation, the reaction proceeds cleanly at room temperature, with complete substrate conversion in 14min.

text: In comparison to RhCl(PHCy), the iridium analogue has reduced catalytic activity on the dehydrogenation of non sterically hindered

text: amine-boranes

text: , and increased activity on more sterically hindered substrates. Dehydrocoupling of primary diborazanes NHR—BH—NHR—BH can be catalyzed by

text: Brookhart's catalyst

text: via conversion to the metal-bound species MeNH—BH and subsequent polymerization/oligomerization. This same reaction has been found to occur in the absence of the iridium metal, upon heating of the reaction mixture. Dehydrogenation of ammonia-borane with Brookhart's catalyst results in quantitative formation of the cyclic pentamer [NHBH] rather than the typically seen cyclic dimers from other amine-borane dehydrogenations. When catalyzing ammonia-borane dehydrogenation, the catalyst acts homogeneously at a 0.5 mol% catalyst loading. Rather than the typical high temperatures needed for this dehydrogenation, the reaction proceeds cleanly at room temperature, with complete substrate conversion in 14min.

text: A laminar flow reactor (LFR) is a type of chemical reactor that uses laminar flow to control reaction rate, and/or reaction distribution. LFR is generally a long tube with constant diameter that is kept at constant temperature. Reactants are injected at one end and products are collected and monitored at the other.  Laminar flow reactors are often used to study an isolated elementary reaction or multi-step reaction mechanism.

text: A laminar flow reactor (LFR) is a type of

text: chemical reactor

text: that uses

text: laminar flow

text: to control

text: reaction rate

text: , and/or reaction distribution. LFR is generally a long tube with constant diameter that is kept at constant temperature. Reactants are injected at one end and products are collected and monitored at the other.  Laminar flow reactors are often used to study an isolated

text: elementary reaction

text: or multi-step

text: reaction mechanism

text: Surface diffusion is a critically important concept in heterogeneous catalysis, as reaction rates are often dictated by the ability of reactants to "find" each other at a catalyst surface. With increased temperature adsorbed molecules, molecular fragments, atoms, and clusters tend to have much greater mobility (see equation 1). However, with increased temperature the lifetime of adsorption decreases as the factor kT becomes large enough for the adsorbed species to overcome the barrier to desorption, Q (see figure 2). Reaction thermodynamics aside because of the interplay between increased rates of diffusion and decreased lifetime of adsorption, increased temperature may in some cases decrease the overall rate of the reaction.

text: Surface diffusion is a critically important concept in heterogeneous catalysis, as reaction rates are often dictated by the ability of reactants to "find" each other at a catalyst surface. With increased temperature adsorbed molecules, molecular fragments, atoms, and clusters tend to have much greater mobility (see equation 1). However, with increased temperature the lifetime of adsorption decreases as the factor kT becomes large enough for the adsorbed species to overcome the barrier to desorption, Q (see figure 2).

text: Reaction

text: thermodynamics

text: aside because of the interplay between increased rates of diffusion and decreased lifetime of adsorption, increased temperature may in some cases decrease the overall rate of the reaction.

text: The speed of the reaction is what distinguishes an explosive reaction from an ordinary combustion reaction. Unless the reaction occurs very rapidly, the thermally expanding gases will be moderately dissipated in the medium, with no large differential in pressure and there will be no explosion. Consider a wood fire. As the fire burns, there certainly is the evolution of heat and the formation of gases, but neither is liberated rapidly enough to build up a sudden substantial pressure differential and then cause an explosion. This can be likened to the difference between the energy discharge of a battery, which is slow, and that of a flash capacitor like that in a camera flash, which releases its energy all at once.

text: The speed of the reaction is what distinguishes an explosive reaction from an ordinary combustion reaction. Unless the reaction occurs very rapidly, the thermally expanding gases will be moderately dissipated in the medium, with no large differential in pressure and there will be no explosion. Consider a wood fire. As the fire burns, there certainly is the evolution of heat and the formation of gases, but neither is liberated rapidly enough to build up a sudden substantial pressure differential and then cause an explosion. This can be likened to the difference between the energy discharge of a

text: battery

text: , which is slow, and that of a flash

text: capacitor

text: like that in a

text: camera

text: flash, which releases its energy all at once.

text: The concentration of DNA can affect the rate of ligation, and whether the ligation is an inter-molecular or intra-molecular reaction.  Ligation involves joining up the ends of a DNA with other ends, however, each DNA fragment has two ends, and if the ends are compatible, a DNA molecule can circularize by joining its own ends.  At high DNA concentration, there is a greater chance of forming intermolecular ligation, while at a lower DNA concentration, intramolecular reaction that circularizes the DNA is more likely.  The transformation efficiency of linear DNA is much lower than circular DNA, and for the DNA to circularize, the DNA concentration should not be too high.  As a general rule, the total DNA concentration should be less than 10 μg/ml.

text: The concentration of DNA can affect the rate of ligation, and whether the ligation is an inter-molecular or intra-molecular reaction.  Ligation involves joining up the ends of a DNA with other ends, however, each DNA fragment has two ends, and if the ends are compatible, a DNA molecule can circularize by joining its own ends.  At high DNA concentration, there is a greater chance of forming intermolecular ligation, while at a lower DNA concentration,

text: intramolecular reaction

text: that circularizes the DNA is more likely.  The

text: transformation efficiency

text: of linear DNA is much lower than circular DNA, and for the DNA to circularize, the DNA concentration should not be too high.  As a general rule, the total DNA concentration should be less than 10 μg/ml.

text: From the reaction rate's temperature dependence an activation energy is determined, and this activation energy is interpreted as the energy of the transition state in a reaction diagram. The latter is drawn, according to Arrhenius and Eyring, as an energy diagram with the reaction coordinate as the abscissa. The reaction coordinate describes the minimum energy path from the reactants to the products, and the points of this coordinate are combinations of distances and angles between and in the reactants in the course of the formation and/or cleavage of bonds. The maximum of the energy diagram, the transition state, is characterized by a specific configuration of the atoms.  Moreover, in Eyring's TST  a quite specific change of the nuclear coordinates is responsible for crossing the maximum point, a vibration in this direction is consequently treated as a translation.

text: From the reaction rate's temperature dependence an

text: activation energy

text: is determined, and this activation energy is interpreted as the energy of the

text: transition state

text: in a reaction diagram. The latter is drawn, according to Arrhenius and Eyring, as an energy diagram with the reaction coordinate as the abscissa. The reaction coordinate describes the minimum energy path from the reactants to the products, and the points of this coordinate are combinations of distances and angles between and in the reactants in the course of the formation and/or cleavage of bonds. The maximum of the energy diagram, the

text: transition state

text: , is characterized by a specific configuration of the atoms.  Moreover, in Eyring's TST  a quite specific change of the

text: nuclear coordinates

text: is responsible for crossing the maximum point, a vibration in this direction is consequently treated as a translation.

text: In enzymology, an isochorismatase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , an isochorismatase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: In enzymology, a triphosphatase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , a triphosphatase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: Increasing the pressure in a gaseous reaction will increase the number of collisions between reactants, increasing the rate of reaction. This is because the activity of a gas is directly proportional to the partial pressure of the gas. This is similar to the effect of increasing the concentration of a solution.

text: Increasing the pressure in a gaseous reaction will increase the number of collisions between reactants, increasing the rate of reaction. This is because the

text: activity

text: of a gas is directly proportional to the partial pressure of the gas. This is similar to the effect of increasing the concentration of a solution.

text: The chemical kinetics of a radical reaction depend on all these individual reactions. In steady state the concentrations of initiating (I) and terminating species T are negligent and rate of initiation and rate of termination are equal. The overall reaction rate can be written as:

text: The

text: chemical kinetics

text: of a radical reaction depend on all these individual reactions. In

text: steady state

text: the concentrations of initiating (I) and terminating species T are negligent and rate of initiation and rate of termination are equal. The overall

text: reaction rate

text: can be written as:

text: MCPs lacking stabilizing groups may generate TMM synthons in the presence of palladium(0) or nickel(0) catalysts. Formal insertion of the catalyst into either of the two chemically distinct cyclopropane bonds (called "distal" and "proximal" to reflect their distance from the double bond) has the potential to generate isomeric products. Generally, palladium catalysts cause formal distal bond cleavage. This process is believed to occur through direct attack of the distal bond on the coordinated alkene. The reaction is stepwise and lacks stereospecificity under both palladium and nickel catalysis.

text: MCPs lacking stabilizing groups may generate TMM synthons in the presence of

text: palladium

text: (0) or

text: nickel

text: (0) catalysts. Formal insertion of the catalyst into either of the two chemically distinct

text: cyclopropane

text: bonds (called "distal" and "proximal" to reflect their distance from the

text: double bond

text: ) has the potential to generate

text: isomer

text: ic products. Generally, palladium catalysts cause formal distal bond cleavage. This process is believed to occur through direct attack of the distal bond on the coordinated alkene. The reaction is stepwise and lacks stereospecificity under both palladium and nickel catalysis.

text: In the catalyzed elementary reaction, catalysts do not change the extent of a reaction: they have no effect on the chemical equilibrium of a reaction because the rate of both the forward and the reverse reaction are both affected (see also thermodynamics).  The second law of thermodynamics describes why a catalyst does not change the chemical equilibrium of a reaction.  Suppose there was such a catalyst that shifted an equilibrium. Introducing the catalyst to the system would result in a reaction to move to the new equilibrium, producing energy. Production of energy is a necessary result since reactions are spontaneous only if Gibbs free energy is produced, and if there is no energy barrier, there is no need for a catalyst. Then, removing the catalyst would also result in reaction, producing energy; i.e. the addition and its reverse process, removal, would both produce energy. Thus, a catalyst that could change the equilibrium would be a perpetual motion machine, a contradiction to the laws of thermodynamics.

text: In the catalyzed

text: elementary reaction

text: , catalysts do not change the extent of a reaction: they have no effect on the

text: chemical equilibrium

text: of a reaction because the rate of both the forward and the reverse reaction are both affected (see also

text: thermodynamics

text: ).  The

text: second law of thermodynamics

text: describes why a catalyst does not change the chemical equilibrium of a reaction.  Suppose there was such a catalyst that shifted an equilibrium. Introducing the catalyst to the system would result in a reaction to move to the new equilibrium, producing energy. Production of energy is a necessary result since reactions are spontaneous only if

text: Gibbs free energy

text: is produced, and if there is no energy barrier, there is no need for a catalyst. Then, removing the catalyst would also result in reaction, producing energy; i.e. the addition and its reverse process, removal, would both produce energy. Thus, a catalyst that could change the equilibrium would be a

text: perpetual motion machine

text: , a contradiction to the laws of thermodynamics.

text: Coordinated ligands display reactivity distinct from the free ligands.  For example, the acidity of the ammonia ligands in [Co(NH)] is elevated relative to NH itself.  Alkenes bound to metal cations are reactive toward nucleophiles whereas alkenes normally are not.  The large and industrially important area of catalysis hinges on the ability of metals to modify the reactivity of organic ligands.  Homogeneous catalysis occurs in solution and heterogeneous catalysis occurs when gaseous or dissolved substrates interact with surfaces of solids.  Traditionally homogeneous catalysis is considered part of organometallic chemistry and heterogeneous catalysis is discussed in the context of surface science, a subfield of solid state chemistry.  But the basic inorganic chemical principles are the same.  Transition metals, almost uniquely, react with small molecules such as CO, H, O, and CH.  The industrial significance of these feedstocks drives the active area of catalysis.  Ligands can also undergo ligand transfer reactions such as transmetalation.

text: Coordinated ligands display reactivity distinct from the free ligands.  For example, the acidity of the ammonia ligands in

text: [Co(NH)]

text: is elevated relative to NH itself.  Alkenes bound to metal cations are reactive toward nucleophiles whereas alkenes normally are not.  The large and industrially important area of

text: catalysis

text: hinges on the ability of metals to modify the reactivity of organic ligands.

text: Homogeneous catalysis

text: occurs in solution and

text: heterogeneous catalysis

text: occurs when

text: gas

text: eous or

text: dissolved

text: substrates interact with surfaces of solids.  Traditionally

text: homogeneous catalysis

text: is considered part of organometallic chemistry and

text: heterogeneous catalysis

text: is discussed in the context of

text: surface science

text: , a subfield of solid state chemistry.  But the basic inorganic chemical principles are the same.  Transition metals, almost uniquely, react with small molecules such as CO, H, O, and CH.  The industrial significance of these feedstocks drives the active area of catalysis.  Ligands can also undergo ligand transfer reactions such as

text: transmetalation

text: Chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. Some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. Understanding chemical changes is a major part of the science of chemistry.

text: Chemical changes occur when a substance combines with another to form a new substance, called

text: chemical synthesis

text: or, alternatively,

text: chemical decomposition

text: into two or more different substances. These processes are called

text: chemical reaction

text: s and, in general, are not reversible except by further chemical reactions. Some reactions produce

text: heat

text: and are called

text: exothermic reaction

text: s and others may require heat to enable the reaction to occur, which are called

text: endothermic reactions

text: . Understanding chemical changes is a major part of the science of

text: chemistry

text: The steady state concept is different from chemical equilibrium. Although both may create a situation where a concentration does not change, in a system at chemical equilibrium, the net reaction rate is zero (products transform into reactants at the same rate as reactants transform into products), while no such limitation exists in the steady state concept. Indeed, there does not have to be a reaction at all for a steady state to develop.

text: The steady state concept is different from

text: chemical equilibrium

text: . Although both may create a situation where a

text: concentration

text: does not change, in a system at chemical equilibrium, the net

text: reaction

text: rate is zero (products transform into reactants at the same rate as reactants transform into products), while no such limitation exists in the steady state concept. Indeed, there does not have to be a reaction at all for a steady state to develop.

text: Steam was in use in many areas of the gasworks, including:For the operation of the exhauster;For scurfing of pyrolysis char and slag from the retorts and for clinkering the producer of the bench;For the operation of engines used for conveying, compressing air, charging hydraulics, or the driving of dynamos or generators producing electric current;To be injected under the grate of the producer in the indirectly fired bench, so as to prevent the formation of clinker, and to aid in the water-gas shift reaction, ensuring high-quality secondary combustion;As a reactant in the (carburetted) water gas plant, as well as driving the equipment thereof, such as the numerous blowers used in that process, as well as the oil spray for the carburettor;For the operation of fire, water, liquid, liquor, and tar pumps;For the operation of engines driving coal and coke conveyor-belts;For clearing of chemical obstructions in pipes, including naphthalene & tar as well as general cleaning of equipment;For heating cold buildings in the works, for maintaining the temperature of process piping, and preventing freezing of the water of the gasholder, or congealment of various chemical tanks and wells.

text: In yeast cells, the interaction of yeast pyruvate kinase (YPK) with PEP and its allosteric effector Fructose 1,6-bisphosphate (FBP,) was found to be enhanced by the presence of Mg. Therefore, Mg was isolated as an important component in the successful catalysis of PEP into pyruvate by pyruvate kinase. Furthermore, the metal ion Mn was shown to have a similar, but stronger effect on the coupling free energy of YPK than Mg. The binding of metal ions to the metal binding sites on pyruvate kinase enhance the rate of this glycolytic reaction. The glycolytic reaction catalyzed by pyruvate kinase is the final step of glycolysis. It is one of the three rate-affecting steps of the catabolic reaction cascade. The rate-affecting steps are the slower steps of a reaction and thus determines the rate of the overall reaction. In glycolysis, the rate-affecting steps are coupled with the hydrolysis of ATP or the phosphorylation of ADP to create the highly energetically favorable and irreversible reaction mechanism. This final step is highly regulated and deliberately irreversible because pyruvate is a crucial intermediate building block for further metabolic pathways. Once pyruvate kinase synthesizes pyruvate, pyruvate either enters the TCA cycle for further production of ATP under aerobic conditions, or is reduced to lactate under anaerobic conditions. Both of these secondary metabolic pathways are essential to the function of the metabolism.

text: In yeast cells, the interaction of yeast pyruvate kinase (YPK) with PEP and its allosteric effector

text: Fructose 1,6-bisphosphate

text: (FBP,) was found to be enhanced by the presence of Mg. Therefore, Mg was isolated as an important component in the successful catalysis of PEP into pyruvate by pyruvate kinase. Furthermore, the metal ion Mn was shown to have a similar, but stronger effect on the coupling free energy of YPK than Mg. The binding of metal ions to the metal binding sites on pyruvate kinase enhance the rate of this glycolytic reaction. The glycolytic reaction catalyzed by pyruvate kinase is the final step of glycolysis. It is one of the three rate-affecting steps of the catabolic reaction cascade. The

text: rate-affecting steps

text: are the slower steps of a reaction and thus determines the rate of the overall reaction. In glycolysis, the rate-affecting steps are coupled with the hydrolysis of ATP or the phosphorylation of ADP to create the highly energetically favorable and irreversible reaction mechanism. This final step is highly regulated and deliberately irreversible because pyruvate is a crucial intermediate building block for further metabolic pathways. Once pyruvate kinase synthesizes pyruvate, pyruvate either enters the

text: TCA cycle

text: for further production of ATP under aerobic conditions, or is reduced to lactate under anaerobic conditions. Both of these secondary metabolic pathways are essential to the function of the metabolism.

text: An example of catalysts of this type is Sander’s porphyrin trimer. A Diels Alder reaction between two pyridine functionalized substrates normally yield a mixture of endo and exo products. In the presence of the two catalysts, however, complete endo selectivity or exo selectivity could be obtained. The underlying cause of the selectivity is the coordination interaction between pyridine and the zinc ion on porphyrin. Depending on the shape of the catalysts, one product is preferred over the other.

text: Corrosion is a major issue with neural electrodes. Corrosion can occur because electrode metals are placed in an electrolytic solution, where the presence of current can either increase the rate of corrosion mechanisms or overcome limiting activation energies. Redox reactions are a mechanism of corrosion that can lead to dissolution of ions from the electrode surface. There is a base level of metal ions in tissue, however, when these levels increase beyond threshold values the ions become toxic and can cause severe health problems. In addition, the fidelity of the electrode system can be compromised. Knowing the impedance of an electrode is important whether the electrode is used for stimulation or recording. When degradation of the electrode surface occurs because of corrosion, the surface area increases with its roughness. Calculating a new electrode impedance to compensate for the change in surface area once implanted it is not easy. This computational flaw can skew data from recording or pose a dangerous obstacle limiting safe stimulation.

text: Corrosion

text: is a major issue with neural electrodes. Corrosion can occur because electrode metals are placed in an electrolytic solution, where the presence of current can either increase the rate of corrosion mechanisms or overcome limiting activation energies.

text: Redox

text: reactions are a mechanism of corrosion that can lead to dissolution of ions from the electrode surface. There is a base level of metal ions in tissue, however, when these levels increase beyond threshold values the ions become toxic and can cause severe health problems. In addition, the fidelity of the electrode system can be compromised. Knowing the impedance of an electrode is important whether the electrode is used for stimulation or recording. When degradation of the electrode surface occurs because of corrosion, the surface area increases with its roughness. Calculating a new electrode impedance to compensate for the change in surface area once implanted it is not easy. This computational flaw can skew data from recording or pose a dangerous obstacle limiting safe stimulation.

text: Before the development of TST, the Arrhenius rate law was widely used to determine energies for the reaction barrier. The Arrhenius equation derives from empirical observations and ignores any mechanistic considerations, such as whether one or more reactive intermediates are involved in the conversion of a reactant to a product.  Therefore, further development was necessary to understand the two parameters associated with this law, the pre-exponential factor (A) and the activation energy (E). TST, which led to the Eyring equation, successfully addresses these two issues; however, 46 years elapsed between the publication of the Arrhenius rate law, in 1889, and the Eyring equation derived from TST, in 1935. During that period, many scientists and researchers contributed significantly to the development of the theory.

text: Before the development of TST, the Arrhenius rate law was widely used to determine energies for the reaction barrier. The

text: Arrhenius equation

text: derives from empirical observations and ignores any mechanistic considerations, such as whether one or more reactive intermediates are involved in the conversion of a reactant to a product.  Therefore, further development was necessary to understand the two parameters associated with this law, the pre-exponential factor (A) and the activation energy (E). TST, which led to the

text: Eyring equation

text: , successfully addresses these two issues; however, 46 years elapsed between the publication of the Arrhenius rate law, in 1889, and the Eyring equation derived from TST, in 1935. During that period, many scientists and researchers contributed significantly to the development of the theory.

text: In the context of organocatalysis both concepts of on-water reactions and in-the-presence-of-water reactions have been criticized in 2007 as not so environmentally friendly by Donna Blackmond. According to Blackmond, separation of reaction product from the water phase usually requires organic solvent anyway and in reported aqueous systems the water phase can in reality be less than 10% of the total reaction mixture with another component forming the actual solvent. Blackmond also notes that in reported instances, the observed rate-acceleration in presence of water is in fact due to water suppressing reaction deactivation.

text: In the context of

text: organocatalysis

text: both concepts of on-water reactions and in-the-presence-of-water reactions have been criticized in 2007 as not so environmentally friendly by Donna Blackmond. According to Blackmond, separation of reaction product from the water phase usually requires organic solvent anyway and in reported aqueous systems the water phase can in reality be less than 10% of the total reaction mixture with another component forming the actual solvent. Blackmond also notes that in reported instances, the observed rate-acceleration in presence of water is in fact due to water suppressing reaction deactivation.

text: This type of inhibition reduces the maximum rate of a chemical reaction without changing the apparent binding affinity of the catalyst for the substrate (K – see Michaelis-Menten kinetics).

text: This type of inhibition reduces the

text: maximum rate

text: of a

text: chemical reaction

text: without changing the apparent binding

text: affinity

text: of the

text: catalyst

text: for the

text: substrate

text: (K – see

text: Michaelis-Menten kinetics

text: For most chemical reactions of industrial interest, it is impossible for the reaction to proceed to 100% completion.  The rate of reaction decreases as the reactants are consumed until the point where the system reaches dynamic equilibrium (no net reaction, or change in chemical species occurs).  The equilibrium point for most systems is less than 100% complete. For this reason a separation process, such as distillation, often follows a chemical reactor in order to separate any remaining reagents or byproducts from the desired product. These reagents may sometimes be reused at the beginning of the process, such as in the Haber process. In some cases, very large reactors would be necessary to approach equilibrium, and chemical engineers may choose to separate the partially reacted mixture and recycle the leftover reactants.

text: For most chemical reactions of industrial interest, it is impossible for the reaction to proceed to 100% completion.  The rate of reaction decreases as the reactants are consumed until the point where the system reaches dynamic equilibrium (no net reaction, or change in chemical species occurs).  The equilibrium point for most systems is less than 100% complete. For this reason a separation process, such as

text: distillation

text: , often follows a chemical reactor in order to separate any remaining reagents or byproducts from the desired product. These reagents may sometimes be reused at the beginning of the process, such as in the

text: Haber process

text: . In some cases, very large reactors would be necessary to approach equilibrium, and

text: chemical engineer

text: s may choose to separate the partially reacted mixture and recycle the leftover reactants.

text: Polyester resin tends to have yellowish tint, and is suitable for most backyard projects. Its weaknesses are that it is UV sensitive and can tend to degrade over time, and thus generally is also coated to help preserve it. It is often used in the making of surfboards and for marine applications. Its hardener is a peroxide, often MEKP (methyl ethyl ketone peroxide).  When the peroxide is mixed with the resin, it decomposes to generate free radicals, which initiate the curing reaction.  Hardeners in these systems are commonly called catalysts, but since they do not re-appear unchanged at the end of the reaction, they do not fit the strictest chemical definition of a catalyst.

text: In enzymology, a mannokinase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , a mannokinase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: In enzymology, a guanidinopropionase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , a guanidinopropionase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: In catalysis, the reaction does not proceed directly, but through reaction with a third substance known as catalyst. Although the catalyst takes part in the reaction, it is returned to its original state by the end of the reaction and so is not consumed. However, it can be inhibited, deactivated or destroyed by secondary processes. Catalysts can be used in a different phase (heterogeneous) or in the same phase (homogeneous) as the reactants. In heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid–liquid system or evaporate in a solid–gas system. Catalysts can only speed up the reaction – chemicals that slow down the reaction are called inhibitors. Substances that increase the activity of catalysts are called promoters, and substances that deactivate catalysts are called catalytic poisons. With a catalyst, a reaction which is kinetically inhibited by a high activation energy can take place in circumvention of this activation energy.

text: In

text: catalysis

text: , the reaction does not proceed directly, but through reaction with a third substance known as

text: catalyst

text: . Although the catalyst takes part in the reaction, it is returned to its original state by the end of the reaction and so is not consumed. However, it can be inhibited, deactivated or destroyed by secondary processes. Catalysts can be used in a different phase (

text: heterogeneous

text: ) or in the same phase (

text: homogeneous

text: ) as the reactants. In heterogeneous catalysis, typical secondary processes include

text: coking

text: where the catalyst becomes covered by

text: polymer

text: ic side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid–liquid system or evaporate in a solid–gas system. Catalysts can only speed up the reaction – chemicals that slow down the reaction are called inhibitors. Substances that increase the activity of catalysts are called promoters, and substances that deactivate catalysts are called catalytic poisons. With a catalyst, a reaction which is kinetically inhibited by a high activation energy can take place in circumvention of this activation energy.

text: A first order reaction depends on the concentration of only one reactant (a unimolecular reaction). Other reactants can be present, but each will be zero order. The rate law for a reaction that is first order with respect to a reactant A is

text: Collision theory is a theory proposed independently by Max Trautz in 1916 and William Lewis in 1918, that qualitatively explains how chemical reactions occur and why reaction rates differ for different reactions. The collision theory states that when suitable particles of the reactant hit each other, only a certain percentage of the collisions cause any noticeable or significant chemical change; these successful changes are called successful collisions. The successful collisions have enough energy, also known as activation energy, at the moment of impact to break the preexisting bonds and form all new bonds. This results in the products of the reaction. Increasing the concentration of the reactant particles or raising the temperature, thus bringing about more collisions and therefore many more successful collisions, increases the rate of reaction.

text: Collision theory is a theory proposed independently by

text: Max Trautz

text: in 1916 and

text: William Lewis

text: in 1918, that qualitatively explains how

text: chemical reactions

text: occur and why

text: reaction rate

text: s differ for different reactions. The collision theory states that when suitable particles of the reactant hit each other, only a certain percentage of the collisions cause any noticeable or significant chemical change; these successful changes are called successful collisions. The successful collisions have enough energy, also known as

text: activation energy

text: , at the moment of impact to break the preexisting bonds and form all new bonds. This results in the products of the reaction. Increasing the concentration of the reactant particles or raising the temperature, thus bringing about more collisions and therefore many more successful collisions, increases the rate of reaction.

text: René Marcelin developed the first theoretical treatment of the rate of chemical reactions that goes beyond a simple empirical description. He showed that the expression of the rate constant given by the Arrhenius equation had to be composed of two terms. In addition to the activation energy term, he considered that there had to be an activation entropy term. In 1910, Rene Marcelin introduced the concept of standard Gibbs energy of activation. In 1912, he treated the progress of a chemical reaction as a motion of a point in phase space. Using Gibbs' statistical-mechanical methods, he obtained an expression similar to the one which he had obtained earlier from thermodynamic consideration. In 1913, René Marcelin was also the first to use the term potential energy surface.  He theorized that the progress of a chemical reaction could be described as a point in a potential energy surface with coordinates in atomic momenta and distances.

text: René Marcelin developed the first theoretical treatment of the

text: rate

text: of

text: chemical reaction

text: s that goes beyond a simple empirical description. He showed that the expression of the

text: rate constant

text: given by the

text: Arrhenius equation

text: had to be composed of two terms. In addition to the

text: activation energy

text: term, he considered that there had to be an

text: activation entropy

text: term. In 1910, Rene Marcelin introduced the concept of standard Gibbs energy of activation. In 1912, he treated the progress of a chemical reaction as a motion of a point in

text: phase space

text: . Using Gibbs' statistical-mechanical methods, he obtained an expression similar to the one which he had obtained earlier from thermodynamic consideration. In 1913, René Marcelin was also the first to use the term

text: potential energy surface

text: .  He theorized that the progress of a chemical reaction could be described as a point in a potential energy surface with coordinates in atomic momenta and distances.

text: In general terms, the free energy change (ΔG) of a reaction determines whether a chemical change will take place, but kinetics describes how fast the reaction is. A reaction can be very exothermic and have a very positive entropy change but will not happen in practice if the reaction is too slow. If a reactant can produce two different products, the thermodynamically most stable one will in general form, except in special circumstances when the reaction is said to be under kinetic reaction control. The Curtin–Hammett principle applies when determining the product ratio for two reactants interconverting rapidly, each going to a different product. It is possible to make predictions about reaction rate constants for a reaction from free-energy relationships.

text: In general terms, the

text: free energy change (ΔG)

text: of a reaction determines whether a chemical change will take place, but kinetics describes how fast the reaction is. A reaction can be very

text: exothermic

text: and have a very positive

text: entropy

text: change but will not happen in practice if the reaction is too slow. If a reactant can produce two different products, the thermodynamically most stable one will in general form, except in special circumstances when the reaction is said to be under

text: kinetic reaction control

text: . The

text: Curtin–Hammett principle

text: applies when determining the product ratio for two reactants interconverting rapidly, each going to a different product. It is possible to make predictions about reaction rate constants for a reaction from

text: free-energy relationship

text: s.

text: A perfect overlay of multiple experiments with the same-excess but different initial substrate loadings suggests that no changes in the active substrate/catalyst concentration occur over the course of the reaction. The failure of the plots to overlay is generally indicative of catalyst activation, deactivation, or product inhibition under the reaction conditions. These cases may be distinguished by the position of the reaction progress curves relative to each other. Intercepting reactions lying below (slower rates at the same substrate concentration) the parent reactions on the rate vs. substrate concentration plot, are indicative of catalyst activation under reaction conditions. Intercepting reactions lying above (faster rates at the same substrate concentration) the parent reactions on the rate vs. substrate concentration plot, are indicative of catalyst deactivation under reaction conditions; further experimentation is necessary to distinguish product inhibition from other forms of catalyst death.

text: Surface area is important in chemical kinetics. Increasing the surface area of a substance generally increases the rate of a chemical reaction. For example, iron in a fine powder will combust, while in solid blocks it is stable enough to use in structures. For different applications a minimal or maximal surface area may be desired.

text: Surface area is important in

text: chemical kinetics

text: . Increasing the surface area of a substance generally increases the

text: rate

text: of a

text: chemical reaction

text: . For example,

text: iron

text: in a fine powder will

text: combust

text: , while in solid blocks it is stable enough to use in structures. For different applications a minimal or maximal surface area may be desired.

text: Some proteins perform largely structural roles. For instance, movements of the proteins actin and myosin ultimately are responsible for the contraction of skeletal muscle. One property many proteins have is that they specifically bind to a certain molecule or class of molecules—they may be extremely selective in what they bind. Antibodies are an example of proteins that attach to one specific type of molecule. In fact, the enzyme-linked immunosorbent assay (ELISA), which uses antibodies, is one of the most sensitive tests modern medicine uses to detect various biomolecules. Probably the most important proteins, however, are the enzymes. Virtually every reaction in a living cell requires an enzyme to lower the activation energy of the reaction. These molecules recognize specific reactant molecules called substrates; they then catalyze the reaction between them. By lowering the activation energy, the enzyme speeds up that reaction by a rate of 10 or more; a reaction that would normally take over 3,000 years to complete spontaneously might take less than a second with an enzyme. The enzyme itself is not used up in the process, and is free to catalyze the same reaction with a new set of substrates. Using various modifiers, the activity of the enzyme can be regulated, enabling control of the biochemistry of the cell as a whole.

text: Some proteins perform largely structural roles. For instance, movements of the proteins

text: actin

text: and

text: myosin

text: ultimately are responsible for the contraction of skeletal muscle. One property many proteins have is that they specifically bind to a certain molecule or class of molecules—they may be extremely selective in what they bind.

text: Antibodies

text: are an example of proteins that attach to one specific type of molecule. In fact, the

text: enzyme-linked immunosorbent assay

text: (ELISA), which uses antibodies, is one of the most sensitive tests modern medicine uses to detect various biomolecules. Probably the most important proteins, however, are the

text: enzyme

text: s. Virtually every reaction in a living cell requires an enzyme to lower the activation energy of the reaction. These molecules recognize specific reactant molecules called

text: substrate

text: s; they then

text: catalyze

text: the reaction between them. By lowering the

text: activation energy

text: , the enzyme speeds up that reaction by a rate of 10 or more; a reaction that would normally take over 3,000 years to complete spontaneously might take less than a second with an enzyme. The enzyme itself is not used up in the process, and is free to catalyze the same reaction with a new set of substrates. Using various modifiers, the activity of the enzyme can be regulated, enabling control of the biochemistry of the cell as a whole.

text: Enzymes catalyze chemical reactions at rates that are astounding relative to uncatalyzed chemistry at the same reaction conditions.  Each catalytic event requires a minimum of three or often more steps, all of which occur within the few milliseconds that characterize typical enzymatic reactions.  According to transition state theory, the smallest fraction of the catalytic cycle is spent in the most important step, that of the transition state.  The original proposals of absolute reaction rate theory for chemical reactions defined the transition state as a distinct species in the reaction coordinate that determined the absolute reaction rate.  Soon thereafter, Linus Pauling proposed that the powerful catalytic action of enzymes could be explained by specific tight binding to the transition state species   Because reaction rate is proportional to the fraction of the reactant in the transition state complex, the enzyme was proposed to increase the concentration of the reactive species.

text: Enzymes catalyze

text: chemical reactions at rates that are astounding relative to uncatalyzed chemistry at the same reaction conditions.  Each catalytic event requires a minimum of three or often more steps, all of which occur within the few milliseconds that characterize typical enzymatic reactions.  According to transition state theory, the smallest fraction of the catalytic cycle is spent in the most important step, that of the transition state.  The original proposals of absolute reaction rate theory for chemical reactions defined the transition state as a distinct species in the reaction coordinate that determined the absolute reaction rate.  Soon thereafter,

text: Linus Pauling

text: proposed that the powerful catalytic action of enzymes could be explained by specific tight binding to the transition state species   Because reaction rate is proportional to the fraction of the reactant in the transition state complex, the enzyme was proposed to increase the concentration of the reactive species.

text: The increases the rate of the reaction as enzyme-substrate interactions align reactive chemical groups and hold them close together. This reduces the entropy of the reactants and thus makes reactions such as ligations or addition reactions more favorable, there is a reduction in the overall loss of entropy when two reactants become a single product.

text: The increases the rate of the reaction as enzyme-substrate interactions align reactive chemical groups and hold them close together. This reduces the

text: entropy

text: of the reactants and thus makes reactions such as ligations or addition reactions more favorable, there is a reduction in the overall loss of entropy when two reactants become a single product.

text: The use of catalysts is of paramount importance in delivering reliable methods of SiO ALD. Without catalysts, surface reactions leading to the formation of SiO are generally very slow and only occur at exceptionally high temperatures. Typical catalysts for SiO ALD include Lewis bases such as NH or pyridine and SiO ; ALD can also be initiated when these Lewis bases are coupled with other silicon precursors such as tetraethoxysilane (TEOS). Hydrogen bonding is believed to occur between the Lewis base and the SiOH* surface species or between the HO based reactant and the Lewis base. Oxygen becomes a stronger nucleophile when the Lewis base hydrogen bonds with the SiOH* surface species because the SiO-H bond is effectively weakened. As such, the electropositive Si atom in the SiCl reactant is more susceptible to nucleophilic attack. Similarly, hydrogen bonding between a Lewis base and an HO reactant make the electronegative O in HO a strong nucleophile that is able to attack the Si in an existing SiCl* surface species. The use of a Lewis base catalyst is more or less a requirement for SiO ALD, as without a Lewis base catalyst, reaction temperatures must exceed 325 °C and pressures must exceed 10 torr. Generally, the most favorable temperature to perform SiO ALD is at 32 °C and a common deposition rate is 1.35 Angstroms per binary reaction sequence. Two surface reactions for SiO ALD, an overall reaction, and a schematic illustrating Lewis base catalysis in SiO ALD are provided below.

text: The use of catalysts is of paramount importance in delivering reliable methods of SiO ALD. Without

text: catalysts

text: , surface reactions leading to the formation of SiO are generally very slow and only occur at exceptionally high temperatures. Typical catalysts for SiO ALD include Lewis bases such as NH or pyridine and SiO ; ALD can also be initiated when these

text: Lewis bases

text: are coupled with other silicon precursors such as

text: tetraethoxysilane

text: (TEOS).

text: Hydrogen bonding

text: is believed to occur between the Lewis base and the SiOH* surface species or between the HO based reactant and the Lewis base. Oxygen becomes a stronger

text: nucleophile

text: when the Lewis base hydrogen bonds with the SiOH* surface species because the SiO-H bond is effectively weakened. As such, the electropositive Si atom in the SiCl reactant is more susceptible to nucleophilic attack. Similarly, hydrogen bonding between a Lewis base and an HO reactant make the electronegative O in HO a strong nucleophile that is able to attack the Si in an existing SiCl* surface species. The use of a Lewis base catalyst is more or less a requirement for SiO ALD, as without a Lewis base catalyst, reaction temperatures must exceed 325 °C and pressures must exceed 10 torr. Generally, the most favorable temperature to perform SiO ALD is at 32 °C and a common deposition rate is 1.35 Angstroms per binary reaction sequence. Two surface reactions for SiO ALD, an overall reaction, and a schematic illustrating Lewis base catalysis in SiO ALD are provided below.

text: On a molecular scale, there are two main competing reaction processes involved in the degradation of cellulose, or wood fuels, in wildfires.  When there is a low amount of moisture in a cellulose fiber, volatilization of the fuel occurs; this process will generate intermediate gaseous products that will ultimately be the source of combustion.  When moisture is present—or when enough heat is being carried away from the fiber, charring occurs. The chemical kinetics of both reactions indicate that there is a point at which the level of moisture is low enough—and/or heating rates high enough—for combustion processes become self-sufficient. Consequently, changes in wind speed, direction, moisture, temperature, or lapse rate at different levels of the atmosphere can have a significant impact on the behavior and growth of a wildfire. Since the wildfire acts as a heat source to the atmospheric flow, the wildfire can modify local advection patterns, introducing a feedback loop between the fire and the atmosphere.

text: On a molecular scale, there are two main competing reaction processes involved in the degradation of

text: cellulose

text: , or wood fuels, in

text: wildfire

text: s.  When there is a low amount of moisture in a cellulose fiber,

text: volatilization

text: of the fuel occurs; this process will generate intermediate gaseous products that will ultimately be the source of

text: combustion

text: .  When moisture is present—or when enough heat is being carried away from the fiber,

text: charring

text: occurs. The

text: chemical kinetics

text: of both reactions indicate that there is a point at which the level of moisture is low enough—and/or heating rates high enough—for combustion processes become self-sufficient. Consequently, changes in wind speed, direction, moisture, temperature, or

text: lapse rate

text: at different levels of the atmosphere can have a significant impact on the behavior and growth of a wildfire. Since the wildfire acts as a heat source to the atmospheric flow, the wildfire can modify local

text: advection

text: patterns, introducing a

text: feedback loop

text: between the fire and the atmosphere.

text: The reaction catalysed by an enzyme uses exactly the same reactants and produces exactly the same products as the uncatalysed reaction. Like other catalysts, enzymes do not alter the position of equilibrium between substrates and products. However, unlike uncatalysed chemical reactions, enzyme-catalysed reactions display saturation kinetics.  For a given enzyme concentration and for relatively low substrate concentrations, the reaction rate increases linearly with substrate concentration; the enzyme molecules are largely free to catalyse the reaction, and increasing substrate concentration means an increasing rate at which the enzyme and substrate molecules encounter one another.  However, at relatively high substrate concentrations, the reaction rate asymptotically approaches the theoretical maximum; the enzyme active sites are almost all occupied and the reaction rate is determined by the intrinsic turnover rate of the enzyme.  The substrate concentration midway between these two limiting cases is denoted by K.

text: The reaction catalysed by an enzyme uses exactly the same reactants and produces exactly the same products as the uncatalysed reaction. Like other

text: catalysts

text: , enzymes do not alter the position of

text: equilibrium

text: between substrates and products. However, unlike uncatalysed chemical reactions, enzyme-catalysed reactions display saturation kinetics.  For a given enzyme concentration and for relatively low substrate concentrations, the reaction rate increases linearly with substrate concentration; the enzyme molecules are largely free to catalyse the reaction, and increasing substrate concentration means an increasing rate at which the enzyme and substrate molecules encounter one another.  However, at relatively high substrate concentrations, the reaction rate

text: asymptotically

text: approaches the theoretical maximum; the enzyme active sites are almost all occupied and the reaction rate is determined by the intrinsic turnover rate of the enzyme.  The substrate concentration midway between these two limiting cases is denoted by K.

text: where the rate is the change in the molar concentration in one second in the rate-determining step of the reaction (the slowest step), [A] is the product of the molar concentration of all the reactants raised to the correct order, known as the reaction order, and k is the reaction constant, which is constant for one given set of circumstances (generally temperature and pressure) and independent of concentration. The greater the reactivity of a compound the higher the value of k and the higher the rate.  For instance, if,

text: where the

text: rate

text: is the change in the molar concentration in one second in the rate-determining step of the reaction (the slowest step), [A] is the product of the molar concentration of all the reactants raised to the correct order, known as the reaction order, and k is the reaction constant, which is constant for one given set of circumstances (generally temperature and pressure) and independent of concentration. The greater the reactivity of a compound the higher the value of k and the higher the rate.  For instance, if,

text: An example of an experiment in which spectrophotometry is used is the determination of the equilibrium constant of a solution.  A certain chemical reaction within a solution may occur in a forward and reverse direction where reactants form products and products break down into reactants.  At some point, this chemical reaction will reach a point of balance called an equilibrium point.  In order to determine the respective concentrations of reactants and products at this point, the light transmittance of the solution can be tested using spectrophotometry.  The amount of light that passes through the solution is indicative of the concentration of certain chemicals that do not allow light to pass through.

text: Additions in the absence of a catalyst or promoter take place only upon heating to 100-130 °C. In the presence of a Lewis acid, the addition will proceed at -78 °C. Reactions must be carried out under an inert atmosphere in anhydrous conditions, but the process is operationally simple and does not require a great deal of special care. Reactions should be carried out in a well-ventilated fume hood, however, as volatile organotin compounds are highly toxic.

text: When a 1-to-1 (one mole of reactant gives one mole of product) chemical reaction (including equilibria) involves a pair of substances with an isosbestic point, the absorbance of the reaction mixture at this wavelength remains invariant, regardless of the extent of reaction (or the position of the chemical equilibrium). This occurs because the two substances absorb light of that specific wavelength to the same extent, and the analytical concentration remains constant.

text: When a 1-to-1 (one

text: mole

text: of

text: reactant

text: gives one

text: mole

text: of

text: product

text: chemical reaction

text: (including

text: equilibria

text: ) involves a pair of substances with an isosbestic point, the absorbance of the reaction mixture at this wavelength remains invariant, regardless of the

text: extent of reaction

text: (or the position of the chemical equilibrium). This occurs because the two substances

text: absorb

text: light of that specific wavelength to the same extent, and the

text: analytical concentration

text: remains constant.

text: The Koch reaction is an organic reaction for the synthesis of tertiary carboxylic acids from alcohols or alkenes. The reaction is a strongly acid-catalyzed carbonylation using carbon monoxide, and typically occurs at high pressures ranging from 50 to 5,000 kPa, often requiring temperatures several hundred degrees higher than room temperature. Generally the reaction is conducted with strong mineral acids such as sulfuric acid, HF or BF. Large scale operations for the fine chemical industry produce almost 150,000 tonnes of Koch acids and their derivatives annually but also generate a great deal of waste, motivating ongoing attempts to use metal, solid acid, and other novel catalysts to enable the use of milder reaction conditions.  Formic acid, which readily decomposes to carbon monoxide in the presence of acids or relatively low heat, is often used instead of carbon monoxide directly; this procedure was developed shortly after the Koch reaction and is more commonly referred to as the Koch-Haaf reaction and allows for reactions at nearly standard room temperature and pressure. Some commonly industrially produced Koch acids include pivalic acid, 2,2-dimethylbutyric acid and 2,2-dimethylpentanoic acid.

text: The Koch reaction is an

text: organic reaction

text: for the

text: synthesis

text: of tertiary

text: carboxylic acids

text: from

text: alcohols

text: or

text: alkenes

text: . The

text: reaction

text: is a strongly

text: acid

text: catalyzed

text: carbonylation

text: using

text: carbon monoxide

text: , and typically occurs at high pressures ranging from 50 to 5,000 k

text: Pa

text: , often requiring temperatures several hundred degrees higher than room temperature. Generally the reaction is conducted with strong mineral acids such as

text: sulfuric acid

text: HF

text: or

text: BF

text: . Large scale operations for the

text: fine chemical

text: industry produce almost 150,000 tonnes of Koch acids and their derivatives annually but also generate a great deal of waste, motivating ongoing attempts to use metal, solid acid, and other novel

text: catalysts

text: to enable the use of milder reaction conditions.

text: Formic acid

text: , which readily decomposes to carbon monoxide in the presence of acids or relatively low heat, is often used instead of carbon monoxide directly; this procedure was developed shortly after the Koch reaction and is more commonly referred to as the Koch-Haaf reaction and allows for reactions at nearly

entity_name: Standard conditions for temperature and pressure

text: standard room temperature and pressure

text: . Some commonly industrially produced Koch acids include

text: pivalic acid

text: , 2,2-dimethylbutyric acid and 2,2-dimethylpentanoic acid.

text: Between 1928 and 1933, Conant published 55 papers. Much of his research, like his double thesis, combined natural product chemistry with physical organic chemistry. Based on his exploration of reaction rates in chemical equilibria, Conant was one of the first to recognise that the kinetics of these systems is sometimes straightforward and simple, yet quite complex in other cases. Conant studied the effect of haloalkane structure on the rate of substitution with inorganic iodide salts<ref>Conant published a series of three papers on the reaction of inorganic iodide with organic halides:

text: Between 1928 and 1933, Conant published 55 papers. Much of his research, like his double thesis, combined

text: natural product

text: chemistry with

text: physical organic chemistry

text: . Based on his exploration of

text: reaction rate

text: s in

text: chemical equilibria

text: , Conant was one of the first to recognise that the

text: kinetics

text: of these systems is sometimes straightforward and simple, yet quite complex in other cases. Conant studied the effect of

text: haloalkane

text: structure on the rate of

text: substitution

text: with inorganic

text: iodide

text: salts

text: <ref>Conant published a series of three papers on the reaction of inorganic iodide with organic halides:

text: In the early stages of the reaction, only a minor amount of the catalyst is activated. As the reaction proceeds, more acetate is generated, which leads to the formation of more activated complex and progressively faster catalysis. This type of behavior is typical for cascade-type reactions including PCR. Unlike the previous example in which the catalyst produced a signal amplifier, this catalyst is a target amplifier making more copies of the target acetate. Following the reaction by gas chromatography, one observes that the generation of products follows a sigmoidal curve, indicative of a PCR-like cascade reaction system.

text: It is fundamental in chemical reactions of the form A+B→ C+D that two products are necessarily generated though product C may have been the desired one. That being the case, D is considered a byproduct. As it is a significant goal of green chemistry to maximize the efficiency of the reactants and minimize the production of waste, D must either be found to have use, be eliminated or be as insignificant and innocuous as possible. With the new equation of the form A+B→C, the first step in making chemical manufacturing more efficient is the use of reactions that resemble simple addition reactions with the only other additions being catalytic materials.

text: Electron Equivalent is a concept commonly used in redox chemistry, reactions involving electron transfer, to define a quantity (e.g. energy or moles) relative to one electron. Energies of formation are often given as kilojoules per electron equivalent to enable calculation of specific reaction energies on a "per electron" basis.  Reactions containing movement of electrons are often balanced such that reaction quantities are given in relation to the transfer of a single electron, allowing quantification of reactants and products in relation to a single electron transfer.

text: Electron Equivalent is a concept commonly used in

text: redox chemistry

text: , reactions involving

text: electron transfer

text: , to define a quantity (e.g. energy or moles) relative to one electron.

text: Energies of formation

text: are often given as kilojoules per electron equivalent to enable calculation of specific reaction energies on a "per electron" basis.  Reactions containing movement of electrons are often balanced such that reaction quantities are given in relation to the transfer of a single electron, allowing quantification of reactants and products in relation to a single electron transfer.

text: A chemical reaction network (often abbreviated to CRN) comprises a set of reactants, a set of products (often intersecting the set of reactants), and a set of reactions. For example, the pair of combustion reactions

text: A chemical reaction network (often abbreviated to CRN) comprises a

text: set

text: of

text: reactants

text: , a set of products (often

text: intersecting

text: the set of reactants), and a set of

text: reactions

text: . For example, the pair of

text: combustion

text: reactions

text: . The number of molecules of each reactant used up each time a reaction occurs is constant, as is the number of molecules produced of each product. These numbers are referred to as the stoichiometry of the reaction, and the difference between the two (i.e. the overall number of molecules used up or produced) is the net stoichiometry. This means that the equation representing the chemical reaction network can be rewritten as

text: . The number of molecules of each reactant used up each time a reaction occurs is constant, as is the number of molecules produced of each product. These numbers are referred to as the

text: stoichiometry

text: of the reaction, and the difference between the two (i.e. the overall number of molecules used up or produced) is the net stoichiometry. This means that the equation representing the chemical reaction network can be rewritten as

text: The concentrations of reactants and products in an equilibrium mixture are determined by the analytical concentrations of the reagents (A and B or C and D) and the equilibrium constant, K. The magnitude of the equilibrium constant depends on the Gibbs free energy change for the reaction. So, when the free energy change is large (more than about 30 kJ mol), then the equilibrium constant is large (log K > 3) and the concentrations of the reactants at equilibrium are very small. Such a reaction is sometimes considered to be an irreversible reaction, although in reality small amounts of the reactants are still expected to be present in the reacting system. A truly irreversible chemical reaction is usually achieved when one of the products exits the reacting system, for example, as does carbon dioxide (volatile) in the reaction

text: The

text: concentration

text: s of reactants and products in an equilibrium mixture are determined by the

text: analytical concentration

text: s of the reagents (A and B or C and D) and the

text: equilibrium constant

text: , K. The magnitude of the equilibrium constant depends on the

text: Gibbs free energy

text: change for the reaction. So, when the free energy change is large (more than about 30 kJ mol), then the equilibrium constant is large (log K > 3) and the concentrations of the reactants at equilibrium are very small. Such a reaction is sometimes considered to be an irreversible reaction, although in reality small amounts of the reactants are still expected to be present in the reacting system. A truly irreversible chemical reaction is usually achieved when one of the products exits the reacting system, for example, as does carbon dioxide (volatile) in the reaction

text: In biochemistry, there has been significant interest in the appropriate mathematical model for chemical reactions occurring in the intracellular medium.  This is in contrast to the initial work done on chemical kinetics, which was in simplified systems where reactants were in a relatively dilute, pH-buffered, aqueous solution.  In more complex environments, where bound particles may be prevented from disassociation by their surroundings, or diffusion is slow or anomalous, the model of mass action does not always describe the behavior of the reaction kinetics accurately.  Several attempts have been made to modify the mass action model, but consensus has yet to be reached.  Popular modifications replace the rate constants with functions of time and concentration.  As an alternative to these mathematical constructs, one school of thought is that the mass action model can be valid in intracellular environments under certain conditions, but with different rates than would be found in a dilute, simple environment .

text: Poisoning involves compounds which bonds chemically to the active surface sites of a catalyst. This may have two effects: the total number of catalytic sites or the fraction of the total surface area that has the capability of promoting reaction always decreases, and the average distance that a reactant molecule must diffuse through the pore structure before undergoing reaction may increase. Poisoned sites can no longer accelerate the reaction with which the catalyst was supposed to catalyze. Large scale production of substances such as ammonia in the Haber–Bosch process include steps to remove potential poisons from the product stream.

text: Poisoning involves compounds which

text: bonds chemically

text: to the active surface sites of a catalyst. This may have two effects: the total number of catalytic sites or the fraction of the total surface area that has the capability of promoting reaction always decreases, and the average distance that a reactant molecule must diffuse through the pore structure before undergoing reaction may increase. Poisoned sites can no longer accelerate the reaction with which the catalyst was supposed to catalyze. Large scale production of substances such as

text: ammonia

text: in the

text: Haber–Bosch process

text: include steps to remove potential poisons from the product stream.

text: The rate of a reaction is always positive. A negative sign is present to indicate that the reactant concentration is decreasing.) The IUPAC recommends that the unit of time should always be the second. The rate of reaction differs from the rate of increase of concentration of a product P by a constant factor (the reciprocal of its stoichiometric number) and for a reactant A by minus the reciprocal of the stoichiometric number. The stoichiometric numbers are included so that the defined rate is independent of which reactant or product species is chosen for measurement. For example if a = 1 and b = 3 then B is consumed three times more rapidly than A, but v = -d[A]/dt = -(1/3)d[B]/dt is uniquely defined.

text: The rate of a reaction is always positive. A

text: negative sign

text: is present to indicate that the reactant concentration is decreasing.) The IUPAC recommends that the unit of time should always be the second. The rate of reaction differs from the rate of increase of concentration of a product P by a constant factor (the reciprocal of its

text: stoichiometric number

text: ) and for a reactant A by minus the reciprocal of the stoichiometric number. The stoichiometric numbers are included so that the defined rate is independent of which reactant or product species is chosen for measurement. For example if a = 1 and b = 3 then B is consumed three times more rapidly than A, but v = -d[A]/dt = -(1/3)d[B]/dt is uniquely defined.

text: Different elements have a different atomic mass, and as collections of single atoms, molecules have a definite molar mass, measured with the unit mole (6.02 × 10 individual molecules, Avogadro's constant). By definition, carbon-12 has a molar mass of 12 g/mol. Thus, to calculate the stoichiometry by mass, the number of molecules required for each reactant is expressed in moles and multiplied by the molar mass of each to give the mass of each reactant per mole of reaction. The mass ratios can be calculated by dividing each by the total in the whole reaction.

text: Different elements have a different

text: atomic mass

text: , and as collections of single atoms, molecules have a definite

text: molar mass

text: , measured with the unit mole (6.02 × 10 individual molecules,

text: Avogadro's constant

text: ). By definition, carbon-12 has a molar mass of 12 g/mol. Thus, to calculate the stoichiometry by mass, the number of molecules required for each reactant is expressed in moles and multiplied by the molar mass of each to give the mass of each reactant per mole of reaction. The mass ratios can be calculated by dividing each by the total in the whole reaction.

text: , such that initial rate of reaction,

text: , such that initial rate of reaction,

text: He has since extended his work on CH activation, to examine the use of basic solvents to facilitate the activation of strong bonds.  The fundamental strategy in this case is to develop catalysts that operate by nucleophilic CH activation that, in contrast of electrophilic CH activation, generates negative charge on the carbon during CH cleavage.  The expectation is that in this case the strongly basic solvent can both activate the catalyst as well as “protect” the alcohol product by deprotonation. This is done by the use of non-innocent ligands that participate in the reaction by protonation or deprotonation. This allowed for the demonstration of the first example of aqueous base accelerated CH activation involving the use of a Ru(IPI)Cl pre-catalyst where IPI = 2,6-diimidizoylpyridine. This strategy has led to demonstration of CH activation by a Ru(II)(IPI)(OH)(H2O) complex dissolved in aqueous KOH. As hoped, it was found that rates of CH activation are accelerated by increasing [KOH].

text: He has since extended his work on

text: CH activation

text: , to examine the use of basic solvents to facilitate the activation of strong bonds.  The fundamental strategy in this case is to develop catalysts that operate by nucleophilic CH activation that, in contrast of electrophilic CH activation, generates negative charge on the carbon during CH cleavage.  The expectation is that in this case the strongly basic solvent can both activate the catalyst as well as “protect” the alcohol product by deprotonation. This is done by the use of non-innocent

text: ligands

text: that participate in the reaction by protonation or deprotonation. This allowed for the demonstration of the first example of aqueous base accelerated CH activation involving the use of a Ru(IPI)Cl pre-catalyst where IPI = 2,6-diimidizoylpyridine. This strategy has led to demonstration of CH activation by a Ru(II)(IPI)(OH)(H2O) complex dissolved in aqueous KOH. As hoped, it was found that rates of CH activation are accelerated by increasing [KOH].

text: Other reactions with apolar reactants such as Ene reactions and Diels-Alder reactions also exhibit rate accelerations. An explanation is not available but it involves hydrogen bonding and the presence of a small amount of dissolved solute. This reaction type is of interest to green chemistry because it greatly reduces the usage of organic solvents, reaction product isolation is relatively easy, and it increases the yields and chemical purity with little extra expenditure, if not less.

text: Other reactions with

text: apolar

text: reactant

text: s such as

text: Ene reaction

text: s and

text: Diels-Alder reaction

text: s also exhibit rate accelerations. An explanation is not available but it involves

text: hydrogen bonding

text: and the presence of a small amount of dissolved solute. This reaction type is of interest to

text: green chemistry

text: because it greatly reduces the usage of organic solvents, reaction product isolation is relatively easy, and it increases the yields and chemical purity with little extra expenditure, if not less.

text: The approach at SEMC is based on the de novo, rational design of new technologies from the ground up through a process involving conceptual design, computational study, and experimental discovery. One of the major emphases within SEMC is the development of new single-site catalysts for the activation and eventual rupture of strong bonds. The goal of new catalysts is to reduce the temperature and pressures required to operate the molecular conversion. Next generation catalysts will be key to lower-temperature processes. Catalysts increase the rate of chemical reactions at lower temperatures and are utilized in very small amounts. There are currently no catalysts that can efficiently convert natural gas, carbon dioxide, nitrogen, oxygen, or water at lower temperatures to useful materials or extract the energy stored in the bonds of these molecules. SEMC is addressing these challenges by designing new catalysts to convert these molecules into products that society uses daily.

text: The approach at SEMC is based on the de novo, rational design of new technologies from the ground up through a process involving conceptual design, computational study, and experimental discovery. One of the major emphases within SEMC is the development of new single-site catalysts for the activation and eventual rupture of strong bonds. The goal of new catalysts is to reduce the temperature and pressures required to operate the molecular conversion. Next generation catalysts will be key to lower-temperature processes.

text: Catalysts

text: increase the rate of

text: chemical reactions

text: at lower temperatures and are utilized in very small amounts. There are currently no catalysts that can efficiently convert natural gas, carbon dioxide, nitrogen, oxygen, or water at lower temperatures to useful materials or extract the energy stored in the bonds of these molecules. SEMC is addressing these challenges by designing new catalysts to convert these molecules into products that society uses daily.

text: Phase conversions like changes of aggregate state, chemical reactions or nuclear reactions transmuting substances, from reactants to products, or diffusion through membranes have an overall energy balance. Especially at constant pressure and constant temperature molar energy balances define the notion of a substance potential or chemical potential or molar Gibbs energy, which gives the energetic information about whether the process is possible or not - in a closed system.

text: Phase

text: conversions like changes of

text: aggregate state

text: chemical reaction

text: s or

text: nuclear reaction

text: s transmuting substances, from

text: reactant

text: s to

text: products

text: , or

text: diffusion

text: through

text: membranes

text: have an overall energy balance. Especially at constant pressure and constant temperature molar energy balances define the notion of a

text: substance potential

text: or

text: chemical potential

text: or molar

text: Gibbs energy

text: , which gives the energetic information about whether the process is possible or not - in a

text: closed system

text: Chemical reaction engineering (reaction engineering or reactor engineering) is a specialty in chemical engineering or industrial chemistry dealing with chemical reactors.  Frequently the term relates specifically to catalytic reaction systems where either a homogeneous or heterogeneous catalyst is present in the reactor.  Sometimes a reactor per se is not present by itself, but rather is integrated into a process, for example in reactive separations vessels, retorts, certain fuel cells, and photocatalytic surfaces. The issue of solvent effects on reaction kinetics is also considered as an integral part.

text: Chemical reaction engineering (reaction engineering or reactor engineering) is a specialty in

text: chemical engineering

text: or industrial chemistry dealing with

text: chemical reactor

text: s.  Frequently the term relates specifically to catalytic reaction systems where either a

text: homogeneous

text: or

text: heterogeneous

text: catalyst

text: is present in the reactor.  Sometimes a reactor per se is not present by itself, but rather is integrated into a

text: process

text: , for example in reactive separations vessels,

text: retort

text: s, certain

text: fuel cell

text: s, and photocatalytic surfaces. The issue of

text: solvent effects

text: on reaction kinetics is also considered as an integral part.

text: NFP is used in the development of a to scale, direct-write nanomanufacturing platform. The platform is capable of constructing complex, highly-functional nanoscale devices from a diverse suite of materials (e.g., nanoparticles, catalysts (increase rate of reaction), biomolecules, and chemical solutions).Demonstrated nanopatterning capabilities include:

text: When applied to In Situ Chemical Oxidation, the collective reaction results in the degradation of contaminants in the presence of  as a catalyst. The overall end result of the process can be described by the following reaction:

text: When applied to In Situ Chemical Oxidation, the collective reaction results in the degradation of contaminants in the presence of  as a

text: catalyst

text: . The overall end result of the process can be described by the following reaction:

text: The A coupling (also known as A3 coupling reaction or the aldehyde-alkyne-amine reaction) is a type of multicomponent reaction involving an aldehyde, an alkyne and an amine which react to give a propargyl-amine. The reaction proceeds via direct dehydrative condensation and requires a metal catalyst, typically based on ruthenium/copper, gold or silver. Chiral catalyst can be used to give an enantioselective reaction, yielding a chiral amine.  The solvent can be water. In the catalytic cycle the metal activates the alkyne to a metal acetylide, the amine and aldehyde combine to form an imine which then reacts with the acetylide in an nucleophilic addition. The reaction type was independently reported by three research groups in 2001 -2002; one report on a similar reaction dates back to 1953.

text: The A coupling (also known as A3 coupling reaction or the aldehyde-alkyne-amine reaction) is a type of

text: multicomponent reaction

text: involving an

text: aldehyde

text: , an

text: alkyne

text: and an

text: amine

text: which react to give a

text: propargyl

text: amine

text: . The reaction proceeds via direct dehydrative condensation and requires a metal

text: catalyst

text: , typically based on

text: ruthenium

text: copper

text: gold

text: or

text: silver

text: . Chiral catalyst can be used to give an enantioselective reaction, yielding a chiral amine.  The solvent can be water. In the

text: catalytic cycle

text: the metal activates the alkyne to a

text: metal acetylide

text: , the amine and aldehyde combine to form an

text: imine

text: which then reacts with the acetylide in an

text: nucleophilic addition

text: . The reaction type was independently reported by three research groups in 2001 -2002; one report on a similar reaction dates back to 1953.

text: K is the equilibrium constant between A and B, and k and k are the rate constants for the formation of C and D, respectively. When the rate of interconversion between A and B is much faster than either k or k, then the Curtin–Hammett principle tells us that the C:D product ratio is not equal to the A:B reactant ratio, but is instead determined by the relative energy of the transition states. If reactants A and B were at identical energies, the reaction would depend only on the energy of the transition states leading to each respective product. However, in a real-world scenario, the two reactants are likely at somewhat different energy levels, although the barrier to their interconversion must be low for the Curtin–Hammett scenario to apply. In this case, the product distribution  depends both on the relative quantity of A and B and on the relative barriers to products C and D.

text: While chemical kinetics is concerned with the rate of a chemical reaction, thermodynamics determines the extent to which reactions occur. In a reversible reaction, chemical equilibrium is reached when the rates of the forward and reverse reactions are equal (the principle of detailed balance) and the concentrations of the reactants and products no longer change. This is demonstrated by, for example, the Haber–Bosch process for combining nitrogen and hydrogen to produce ammonia. Chemical clock reactions such as the Belousov–Zhabotinsky reaction demonstrate that component concentrations can oscillate for a long time before finally attaining the equilibrium.

text: While chemical kinetics is concerned with the rate of a chemical reaction,

text: thermodynamics

text: determines the extent to which reactions occur. In a

text: reversible reaction

text: , chemical equilibrium is reached when the rates of the forward and reverse reactions are equal (the principle of

text: detailed balance

text: ) and the concentrations of the

text: reactant

text: s and

text: products

text: no longer change. This is demonstrated by, for example, the

text: Haber–Bosch process

text: for combining nitrogen and hydrogen to produce ammonia.

text: Chemical clock

text: reactions such as the

text: Belousov–Zhabotinsky reaction

text: demonstrate that component concentrations can oscillate for a long time before finally attaining the equilibrium.

text: Nanopowders produced from LF-FSP can be used for several catalytic applications. If nanocatalysts aggregate, their activity is lower due to the decrease in surface area. LF-FSP allows the production of nanocatalyst with minimal aggregation. It is known that bimetallic and trimetallic catalysts offer improved properties over single metal catalysts. Bimetallic nanocatalysts have been produced via LF-FSP. NiO-CoO, NiO-MoO, and NiO-CuO are used for several types of catalytic reactions. For example, NiO-CoO nanoparticles are used as catalysts for the production of fuels and chemicals, and the reduction of environmental pollution. CeO/ZrO catalysts have been studied for automotive catalytic converters. CeO/ZrO catalysts have been added to catalytic systems for the elimination and reduction of the pollutants contained in the exhaust gases of vehicles.

text: Epoxy is a term used to denote both the basic components and the cured end products of epoxy resins, as well as a colloquial name for the epoxide functional group.  Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups.  Epoxy resins may be reacted (cross-linked) either with themselves through catalytic homopolymerisation, or with a wide range of  co-reactants including polyfunctional amines, acids (and acid anhydrides), phenols, alcohols and thiols.  These co-reactants are often referred to as hardeners or curatives, and the cross-linking reaction is commonly referred to as curing.  Reaction of polyepoxides with themselves or with polyfunctional hardeners forms a thermosetting polymer, often with high mechanical properties, temperature and chemical resistance.  Epoxy has a wide range of applications, including metal coatings, use in electronics / electrical components/LED, high tension electrical insulators, paint brushes manufacturing,  fiber-reinforced plastic materials and structural adhesives.

text: Epoxy is a term used to denote both the basic components and the cured end products of epoxy resins, as well as a colloquial name for the

text: epoxide

text: functional group.  Epoxy resins, also known as polyepoxides, are a class of reactive

text: prepolymer

text: s and

text: polymer

text: s which contain epoxide groups.  Epoxy resins may be reacted (

text: cross-linked

text: ) either with themselves through catalytic homopolymerisation, or with a wide range of  co-reactants including polyfunctional amines, acids (and acid anhydrides), phenols, alcohols and thiols.  These co-reactants are often referred to as hardeners or curatives, and the cross-linking reaction is commonly referred to as curing.  Reaction of polyepoxides with themselves or with polyfunctional hardeners forms a

text: thermoset

text: ting

text: polymer

text: , often with high mechanical properties, temperature and chemical resistance.  Epoxy has a wide range of applications, including metal coatings, use in electronics / electrical components/LED, high tension electrical insulators, paint brushes manufacturing,

text: fiber-reinforced plastic

text: materials and structural

text: adhesive

text: s.

text: For reactions which take at least several minutes, it is possible to start the observations after the reactants have been mixed at the temperature of interest.

text: The term Flame retardants subsumes a diverse group of chemicals which are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants inhibit or delay the spread of fire by suppressing the chemical reactions in the flame or by the formation of a protective layer on the surface of a material. They may be mixed with the base material (additive flame retardants) or chemically bonded to it (reactive flame retardants). Mineral flame retardants are typically additive while organohalogen and organophosphorus compounds can be either reactive or additive.

text: The term Flame retardants subsumes a diverse group of chemicals which are added to manufactured materials, such as

text: plastics

text: and textiles, and surface finishes and coatings. Flame retardants inhibit or delay the spread of fire by suppressing the chemical reactions in the flame or by the formation of a protective layer on the surface of a material. They may be mixed with the base material (additive flame retardants) or chemically bonded to it (reactive flame retardants). Mineral flame retardants are typically additive while organohalogen and organophosphorus compounds can be either reactive or additive.

text: Although, a reaction co-ordinate diagram is essentially derived from a potential energy surface, it is not always feasible to draw one from a PES. A chemist draws a reaction co-ordinate diagram for a reaction based on the knowledge of free energy or enthalpy change associated with the transformation which helps him to place the reactant and product into perspective and whether any intermediate is formed or not. One guideline for drawing diagrams for complex reactions is the principle of least motion which says that a favored reaction proceeding from a reactant to an intermediate or from one intermediate to another or product is one which has the least change in nuclear position or electronic configuration. Thus, it can be said that the reactions involving dramatic changes in position of nuclei actually occur through a series of simple chemical reactions. Hammond postulate is another tool which assists in drawing the energy of a transition state relative to a reactant, an intermediate or a product. It states that the transition state resembles the reactant, intermediate or product that it is closest in energy to, as long the energy difference between the transition state and the adjacent structure is not too large. This postulate helps to accurately predict the shape of a reaction co-ordinate diagram and also gives an insight into the molecular structure at the transition state.

text: Although, a reaction co-ordinate diagram is essentially derived from a potential energy surface, it is not always feasible to draw one from a PES. A chemist draws a reaction co-ordinate diagram for a reaction based on the knowledge of free energy or enthalpy change associated with the transformation which helps him to place the reactant and product into perspective and whether any intermediate is formed or not. One guideline for drawing diagrams for complex reactions is the

text: principle of least motion

text: which says that a favored reaction proceeding from a reactant to an intermediate or from one intermediate to another or product is one which has the least change in nuclear position or electronic configuration. Thus, it can be said that the reactions involving dramatic changes in position of nuclei actually occur through a series of simple chemical reactions.

text: Hammond postulate

text: is another tool which assists in drawing the energy of a transition state relative to a reactant, an intermediate or a product. It states that the transition state resembles the reactant, intermediate or product that it is closest in energy to, as long the energy difference between the transition state and the adjacent structure is not too large. This postulate helps to accurately predict the shape of a reaction co-ordinate diagram and also gives an insight into the molecular structure at the transition state.

text: By contrast, polyester resins are usually made available in a 'promoted' form, such that the progress of previously-mixed resins from liquid to solid is already underway, albeit very slowly. The only variable available to the user is to change the rate of this process using a catalyst, often Methyl-Ethyl-Ketone-Peroxide (MEKP), which is very toxic. The presence of the catalyst in the final product actually detracts from the desirable properties, so that small amounts of catalyst are preferable, so long as the hardening proceeds at an acceptable pace. The rate of cure of polyesters can therefore be controlled by the amount and type of catalyst as well as by the temperature.

text: By contrast, polyester resins are usually made available in a 'promoted' form, such that the progress of previously-mixed resins from liquid to solid is already underway, albeit very slowly. The only variable available to the user is to change the rate of this process using a catalyst, often Methyl-Ethyl-Ketone-Peroxide (

text: MEKP

text: ), which is very toxic. The presence of the catalyst in the final product actually detracts from the desirable properties, so that small amounts of catalyst are preferable, so long as the hardening proceeds at an acceptable pace. The rate of cure of polyesters can therefore be controlled by the amount and type of catalyst as well as by the temperature.

text: Franciscus Donders used mental chronometry to study attention and it was considered a major field of intellectual inquiry by authors such as Sigmund Freud. Donders and his students conducted the first detailed investigations of the speed of mental processes. Donders measured the time required to identify a stimulus and to select a motor response. This was the time difference between stimulus discrimination and response initiation.  Donders also formalized the subtractive method which states that the time for a particular process can be estimated by adding that process to a task and taking the difference in reaction time between the two tasks. He also differentiated between three types of reactions: simple reaction, choice reaction, and go/no-go reaction.

text: Franciscus Donders

text: used

text: mental chronometry

text: to study attention and it was considered a major field of intellectual inquiry by authors such as

text: Sigmund Freud

text: . Donders and his students conducted the first detailed investigations of the speed of mental processes. Donders measured the time required to identify a stimulus and to select a motor response. This was the time difference between stimulus discrimination and response initiation.  Donders also formalized the subtractive method which states that the time for a particular process can be estimated by adding that process to a task and taking the difference in reaction time between the two tasks. He also differentiated between

text: three types of reactions

text: : simple reaction, choice reaction, and go/no-go reaction.

text: Similarly, a difference in chemical potential between groups of particles in the system drives a chemical reaction that changes the numbers of particles, and the corresponding product is the amount of chemical potential energy transformed in process. For example, consider a system consisting of two phases: liquid water and water vapor. There is a generalized "force" of evaporation that drives water molecules out of the liquid. There is a generalized "force" of condensation that drives vapor molecules out of the vapor. Only when these two "forces" (or chemical potentials) are equal is there equilibrium, and the net rate of transfer zero.

text: Variational transition-state theory is a refinement of transition-state theory.  When using transition-state theory to estimate a chemical reaction rate, the dividing surface is taken to be a surface that intersects a first-order saddle point and is also perpendicular to the reaction coordinate in all other dimensions.  When using variational transition-state theory, the position of the dividing surface between reactant and product regions is variationally optimized to minimize the reaction rate.  This minimizes the effects of recrossing, and gives a much more accurate result.

text: Variational transition-state theory is a refinement of

text: transition-state theory

text: .  When using transition-state theory to estimate a chemical reaction rate, the dividing surface is taken to be a surface that intersects a first-order saddle point and is also perpendicular to the reaction coordinate in all other dimensions.  When using variational transition-state theory, the position of the dividing surface between reactant and product regions is variationally optimized to minimize the reaction rate.  This minimizes the effects of recrossing, and gives a much more accurate result.

text: The third chapter is named "Maxwell's Demons". It starts off by stating that proteins are the molecular agents of teleonomic performance in living beings. Monod continues by writing that living beings are chemical machines, every organism constitutes a coherent and functional unit, and that the organism is a self-constructing machine whose macroscopic structure is not determined by outside forces but by autonomous internal interactions. The author spends much of the chapter reviewing general facts of biochemistry. He explains that proteins are composed of 100-10,000 amino acids and he distinguishes between elongated fibrous proteins that play a mechanical role and the more numerous globular proteins that are folded upon themselves. He talks about the extraordinary specificity of action that enzymes display as exemplified by their ability to not only recognize a specific geometric isomer but an optical isomer as well. He points out that enzymes are optically active themselves, L isomers are the "natural" isomers, and that the specificity of action and the sterospecificity of the reaction conducted by an enzyme are the result of the positioning of the molecules with respect to each other. Monod writes that an enzymatic reaction can be seen in two steps: The formation of a sterospecific complex between protein and substrate and the catalytic activation of a reaction within the complex (he stresses again that the reaction is oriented and specified by the structure of the complex). He next considers the energetic differences between covalent and non-covalent bonds and how the speed of a reaction is affected by activation energy. Since the activation energy of a covalent bond is high the reaction will have a slower speed than that of a non-covalent bond (which occurs spontaneously and rapidly). The author points out that non-covalent interactions attain stability only through numerous interactions and when applied over short distances. To attain stable non-covalent interaction there is a need for complementary sites between two interacting molecules so as to permit several atoms of the one to enter into contact with several atoms of the other. In this complex the molecule of substrate is strictly positioned by the multiple non-covalent interactions with the enzyme. Enzymatic catalysis is believed to result from the inductive and polarizing action of certain chemical groupings of the specific receptor. By virtue of an enzymes capacity to form sterospecific and non-covalent complexes with specific substrate the substrate is correctly presented in the precise orientation that specifies the catalytic effect of the enzyme. Monod reminds us that this reaction comes at the expense of chemical potential energy.

text: In its usual format, SHS is conducted starting from finely powdered reactants that are intimately mixed.  In some cases, the reagents are finely powdered whereas in other cases, they are sintered to minimize their surface area and prevent uninitiated exothermic reactions, which can be dangerous. In other cases, the particles are mechanically activated through techniques such as ball milling, which results in nanocomposite particles that contain both reactants within individual chemical cells. After reactant preparation, synthesis is initiated by point-heating of a small part (usually the top) of the sample. Once started, a wave of exothermic reaction sweeps through the remaining material. SHS has also been conducted with thin films, liquids, gases, powder–liquid systems, gas suspensions, layered systems, gas-gas systems, and others.  Reactions have been conducted in a vacuum and under both inert or reactive gases.  The temperature of the reaction can be moderated by the addition of inert salt that absorbs heat in the process of melting or evaporation, such as sodium chloride.

text: In its usual format, SHS is conducted starting from finely powdered reactants that are intimately mixed.  In some cases, the reagents are finely powdered whereas in other cases, they are

text: sintered

text: to minimize their surface area and prevent uninitiated exothermic reactions, which can be dangerous. In other cases, the particles are

text: mechanically activated

text: through techniques such as

text: ball milling

text: , which results in

text: nanocomposite

text: particles that contain both reactants within individual chemical cells. After reactant preparation, synthesis is initiated by point-heating of a small part (usually the top) of the sample. Once started, a wave of exothermic reaction sweeps through the remaining material. SHS has also been conducted with thin films, liquids, gases, powder–liquid systems, gas suspensions, layered systems, gas-gas systems, and others.  Reactions have been conducted in a vacuum and under both inert or reactive gases.  The temperature of the reaction can be moderated by the addition of inert salt that absorbs heat in the process of melting or evaporation, such as

text: sodium chloride

text: In simple terms, the ‘Barking Dog’ reaction is a combustion process, in which a fuel (carbon disulfide, CS) reacts with an oxidizing agent (nitrous oxide, NO), producing heat and elemental sulfur.  The flame front in the reaction is a zone of very hot, luminous gas, produced by the reactants decomposing.

text: In simple terms, the ‘Barking Dog’ reaction is a

text: combustion

text: process, in which a fuel (

text: carbon disulfide

text: , CS) reacts with an

text: oxidizing agent

text: nitrous oxide

text: , NO), producing heat and elemental

text: sulfur

text: .  The flame front in the reaction is a zone of very hot,

text: luminous

text: gas, produced by the reactants decomposing.

text: In enzymology, an agmatinase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , an agmatinase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: The Wacker process or the Hoechst-Wacker process (named after the chemical companies of the same name) refers to the oxidation of ethylene to acetaldehyde in the presence of palladium(II) chloride as the catalyst. This chemical reaction was one of the first homogeneous catalysis with organopalladium chemistry applied on an industrial scale.

text: The Wacker process or the Hoechst-Wacker process (named after the chemical companies of the same name) refers to the oxidation of

text: ethylene

text: to

text: acetaldehyde

text: in the presence of

text: palladium(II) chloride

text: as the

text: catalyst

text: . This

text: chemical reaction

text: was one of the first

text: homogeneous catalysis

text: with

text: organopalladium

text: chemistry applied on an industrial scale.

text: A zero order reaction has a rate that is independent of the concentration of the reactant(s). Increasing the concentration of the reacting species will not speed up the rate of the reaction i.e. the amount of substance reacted is proportional to the time. Zero order reactions are typically found when a material that is required for the reaction to proceed, such as a surface or a catalyst, is saturated by the reactants. The rate law for a zero order reaction is

text: A zero order reaction has a rate that is independent of the concentration of the reactant(s). Increasing the concentration of the reacting species will not speed up the rate of the reaction i.e. the amount of substance reacted is proportional to the time. Zero order reactions are typically found when a material that is required for the reaction to proceed, such as a surface or a

text: catalyst

text: , is saturated by the reactants. The rate law for a zero order reaction is

text: Chemical tests use reagents to indicate the presence of a specific chemical in an unknown solution. The reagents cause a unique reaction to occur based on the chemical it reacts with, allowing one to know what chemical is in the solution. An example is Heller's test where a test tube containing proteins has strong acids added to it. A cloudy ring forms where the substances meet, indicating the acids are denaturing the proteins. The cloud is a sign that proteins are present in a liquid. The method is used to detect proteins in a person's urine.

text: Chemical tests

text: use reagents to indicate the presence of a specific chemical in an unknown solution. The reagents cause a unique reaction to occur based on the chemical it reacts with, allowing one to know what chemical is in the solution. An example is Heller's test where a test tube containing proteins has strong acids added to it. A cloudy ring forms where the substances meet, indicating the acids are denaturing the proteins. The cloud is a sign that proteins are present in a liquid. The method is used to detect proteins in a person's urine.

text: This enzyme catalyzes the chemical reaction

text: This

text: enzyme

text: catalyzes

text: the

text: chemical reaction

text: The reaction with the surface is dependent on the chemical species involved.  Applying the Gibbs energy equation for reactions:

text: The reaction with the surface is dependent on the chemical species involved.  Applying the

text: Gibbs energy

text: equation for reactions:

text: Concurrent tandem catalysis (CTC) is a technique in chemistry which uses multiple catalysts on a single molecule in a one-pot reaction to produce a product otherwise not accessible by a single catalyst. Scheme 1 illustrates this process. Molecule A enters this catalytic system to produce the comonomer, B, which along with A enters the next catalytic process to produce the final product, P. This one-pot approach can decrease product loss from isolation or purification of intermediates. Reactions with relatively unstable products can be generated as intermediates because they are only transient species and are immediately used in a consecutive reaction.

text: Concurrent tandem catalysis (CTC) is a technique in

text: chemistry

text: which uses multiple

text: catalyst

text: s on a single molecule in a

text: one-pot reaction

text: to produce a product otherwise not accessible by a single catalyst. Scheme 1 illustrates this process. Molecule A enters this catalytic system to produce the

text: comonomer

text: , B, which along with A enters the next catalytic process to produce the final product, P. This one-pot approach can decrease product loss from isolation or purification of

text: intermediate

text: s. Reactions with relatively unstable

text: product

text: s can be generated as intermediates because they are only transient species and are immediately used in a consecutive

text: reaction

text: In enzymology, an inulosucrase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , an inulosucrase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: In 1864, Peter Waage and Cato Guldberg pioneered the development of chemical kinetics by formulating the law of mass action, which states that the speed of a chemical reaction is proportional to the quantity of the reacting substances.

text: In 1864,

text: Peter Waage

text: and

text: Cato Guldberg

text: pioneered the development of chemical kinetics by formulating the

text: law of mass action

text: , which states that the speed of a chemical reaction is proportional to the quantity of the reacting substances.

text: The center is studying hydrothermal growth process of ZnO nanorods for the last few years. A typical process was carried out in a sealed chemical bath containing an equimolar solution of zinc nitrate hexahydrate and hexamethylene tetramine at a temperature of 95 °C for a period of up to 20 hours. The thickness and length of the nanowires can be controlled by using different concentrations of the starting reactants and growth durations. A 0.5 mM chemical bath yielded nanowires with an average diameter of around 50 nm while a 25 mM bath resulted in wires with a thickness of up to about 1μm. The length of the wires depends both on the concentration of the precursor solution as well as the growth duration, and in 20 hours, nanowires as long as 10 µm can be grown.

text: The catalyst is a substance, usually used in small amounts relative to the reactants, that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. One or more kinds of catalysts can be loaded on another material with a high surface area, which serves as the support, to form a supported catalyst as a whole system. In a supported catalyst system, the significance of using the support are to increase the dispersion of the active phases, to have a better control of the porous structure, to improve mechanical strength, to prevent sintering and to assist catalysis. There is a wide spectrum of supports ranging from conventional and most commonly alumina to novel various kinds of activated carbon. Synthesis methods and functions vary greatly due to different kinds of support and catalytic materials.

text: The

text: catalyst

text: is a substance, usually used in small amounts relative to the reactants, that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. One or more kinds of catalysts can be loaded on another material with a high surface area, which serves as the support, to form a supported catalyst as a whole system. In a supported catalyst system, the significance of using the support are to increase the dispersion of the active phases, to have a better control of the porous structure, to improve mechanical strength, to prevent sintering and to assist catalysis. There is a wide spectrum of supports ranging from conventional and most commonly alumina to novel various kinds of activated carbon. Synthesis methods and functions vary greatly due to different kinds of support and catalytic materials.

text: Through a mechanochemical reaction process, β-CN can be synthesized. This method is achieved by ball milling high purity graphite powders down to an amorphous nanoscale size while under an argon atmosphere, then the argon is purged and the graphite powders are introduced to an NH gas atmosphere, which after high energy ball milling, has been found to form a nanosized flake-like structure of β-CN. During milling, fracture and welding of the reactants and graphite powder particles occur repeatedly from ball/powder collisions. Plastic deformation of the graphite powder particles occur due to the shear bands decomposing into sub-grains that are separated by low-angle grain boundaries, further milling decreases the sub-grain size until nanosize sub-grains form. The high pressure and intense motion promotes catalytic dissociation of NH molecules into monatomic nitrogen on the fractured surface of the carbon. Nanosized carbon powders act substantially different from its bulk material as a result of particle dimension and surface area, causing the nanosized carbon to easily react with the free nitrogen atoms, forming β-CN powder.

text: Through a mechanochemical reaction process, β-CN can be synthesized. This method is achieved by ball milling high purity graphite powders down to an amorphous nanoscale size while under an argon atmosphere, then the argon is purged and the graphite powders are introduced to an NH gas atmosphere, which after high energy

text: ball milling

text: , has been found to form a nanosized flake-like structure of β-CN. During milling, fracture and welding of the reactants and graphite powder particles occur repeatedly from ball/powder collisions.

text: Plastic deformation

text: of the graphite powder particles occur due to the shear bands decomposing into sub-grains that are separated by low-angle grain boundaries, further milling decreases the sub-grain size until nanosize sub-grains form. The high pressure and intense motion promotes

text: catalytic

text: dissociation of NH molecules into

text: monatomic

text: nitrogen on the fractured surface of the carbon. Nanosized carbon powders act substantially different from its bulk material as a result of particle dimension and surface area, causing the nanosized carbon to easily react with the free nitrogen atoms, forming β-CN powder.

text: Catalysts: There are two types of catalysts, positive and negative. Positive catalysts increase the reaction rate and negative catalysts (or inhibitors) slow down a reaction and possibly cause the reaction not occur at all. The purpose of a catalyst is to alter the activation energy. Figure 12 illustrates the purpose of a catalyst in that only the activation energy is changed and not the relative thermodynamic stabilities, shown in the figure as ΔH, of the products and reactants. This means that a catalyst will not alter the equilibrium concentrations of the products and reactants but will only allow the reaction to reach equilibrium faster. Figure 13 shows the catalyzed pathway occurring in multiple steps which is a more realistic depiction of a catalyzed process. The new catalyzed pathway can occur through the same mechanism as the uncatalyzed reaction or through an alternate mechanism. An enzyme is a biological catalyst that increases the rate for many vital biochemical reactions. Figure 13 shows a common way to illustrate the effect of an enzyme on a given biochemical reaction.

text: Catalysts: There are two types of

text: catalysts

text: , positive and negative. Positive catalysts increase the reaction rate and negative catalysts (or inhibitors) slow down a reaction and possibly cause the reaction not occur at all. The purpose of a catalyst is to alter the activation energy. Figure 12 illustrates the purpose of a catalyst in that only the

text: activation energy

text: is changed and not the relative thermodynamic stabilities, shown in the figure as ΔH, of the products and reactants. This means that a catalyst will not alter the equilibrium concentrations of the products and reactants but will only allow the reaction to reach equilibrium faster. Figure 13 shows the catalyzed pathway occurring in multiple steps which is a more realistic depiction of a catalyzed process. The new catalyzed pathway can occur through the same mechanism as the uncatalyzed reaction or through an alternate mechanism. An

text: enzyme

text: is a biological catalyst that increases the rate for many vital biochemical reactions. Figure 13 shows a common way to illustrate the effect of an enzyme on a given biochemical reaction.

text: Reactions A and B are minor and require acidic conditions. Reaction C proceeds in neutral or alkaline pH and is self-accelerating, as it is catalysed by the alcohol formed as a product. Its rate increases with concentration of the reagents and with temperature, from 1.1%/day at 20 °C to 4.6%/day at 40 °C for a 10% solution at pH=10. A decrease in pH from 10 to 6.5 increases the decomposition rate from 1.1%/day to 16%/day. Decomposition is also accelerated by the presence of metals, such as copper, iron, lead or zinc, which act as a catalyst.

text: He became part of the Manhattan Project at Columbia University, where he worked on methods to achieve the separation of the uranium-235 from the more plentiful isotope urainium-238 needed to complete an atomic bomb using the enriched uranium. The method of photochemistry that Bigeleisen researched did not lead to an effective method of separating the uranium isotopes, and gaseous diffusion and methods that took advantage of the electromagnetic properties of uranium proved to be more effective means of isotope separation. Bigeleisen's research led to the development of isotope chemistry based on the principle that heavier isotopes formed stronger chemical bonds allowing for the creation of a straightforward theory to explain the progress of chemical reactions through the interaction of isotopes in gaseous form, which he did together with Maria Goeppert-Mayer, who would later win the Nobel Prize in Physics. Chemists can gain a better understanding of a chemical reaction by using different isotopes to analyze the differing reaction rates, which has allowed for advances in chemical physics, geochemistry and molecular biology. Bigeleisen developed the basic theories of the effect of isotopic substitution on chemical equilibrium and on reaction rates (kinetic isotope effect).

text: He became part of the Manhattan Project at

text: Columbia University

text: , where he worked on methods to achieve the separation of the uranium-235 from the more plentiful isotope urainium-238 needed to complete an atomic bomb using the

text: enriched uranium

text: . The method of photochemistry that Bigeleisen researched did not lead to an effective method of separating the uranium isotopes, and

text: gaseous diffusion

text: and methods that took advantage of the electromagnetic properties of uranium proved to be more effective means of

text: isotope separation

text: . Bigeleisen's research led to the development of isotope chemistry based on the principle that heavier isotopes formed stronger

text: chemical bond

text: s allowing for the creation of a straightforward theory to explain the progress of chemical reactions through the interaction of isotopes in gaseous form, which he did together with

text: Maria Goeppert-Mayer

text: , who would later win the

text: Nobel Prize in Physics

text: . Chemists can gain a better understanding of a chemical reaction by using different isotopes to analyze the differing reaction rates, which has allowed for advances in

text: chemical physics

text: geochemistry

text: and

text: molecular biology

text: . Bigeleisen developed the basic theories of the effect of isotopic substitution on chemical equilibrium and on reaction rates (

text: kinetic isotope effect

text: is the consumption rate of A, a reactant. This is equal to the rate expression A is involved in. The rate expression is often related to the fractional conversion both through the consumption of A and through any k changes through temperature changes that are dependent on conversion.

text: For a chemical reaction a A + b B → p P + q Q, the rate equation or rate law is a mathematical expression used in chemical kinetics to link the rate of a reaction to the concentration of each reactant. It is often of the type:

text: For a

text: chemical reaction

text: a A + b B → p P + q Q, the rate equation or rate law is a

text: mathematical expression

text: used in chemical kinetics to link the rate of a reaction to the

text: concentration

text: of each reactant. It is often of the type:

text: In enzymology, a pentanamidase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , a pentanamidase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: The hypothesis that reaction rate is proportional to reactant concentrations is, strictly speaking, only true for elementary reactions (reactions with a single mechanistic step), but the empirical rate expression

text: The hypothesis that reaction rate is proportional to reactant concentrations is, strictly speaking, only true for

text: elementary reaction

text: s (reactions with a single mechanistic step), but the empirical rate expression

text: The production of [ML] in the reaction above by the "following" chemical reaction produces a species directly at the electrode that could display redox chemistry anywhere in a CV plot or none at all.  The change in coordination from [ML] to [ML] often prevents the observation of "reversible" behavior during electrochemical experiments like cyclic voltammetry.  On the forward scan the expected diffusion wave is observed, in example above the reduction of [ML] to [ML].  However on the return scan the corresponding wave is not observed, in the example above this would be the wave corresponding to the oxidation of [ML] to [ML].  In our example there is no [ML] to oxidize since it has been converted to [ML] through ligand loss.  The return wave can sometimes be observed by increasing the scan rates so the following chemical reaction can be observed before the chemical reaction takes place.  This often requires the use of ultramicroelectrodes (UME) capable of very high scan rates of 0.5 to 5.0 V/s.  Plots of forward and reverse peak ratios against modified forms of the scan rate often identify the rate of the chemical reaction.  It has become a common practice to model such plots with electrochemical simulations.  The results of such studies are of disputed practical relevance since simulation requires excellent experimental data, better than that routinely obtained and reported. Furthermore the parameters of such studies are rarely reported and often include an unreasonably high variable to data ratio (ref?).  A better practice is to look for a simple, well documented relationship between observed results and implied phenomena; or to investigate a specific physical phenomenon using an alternative technique such as chronoamperometry or those involving a rotating electrode.

text: The production of [ML] in the reaction above by the "following" chemical reaction produces a species directly at the electrode that could display redox chemistry anywhere in a CV plot or none at all.  The change in coordination from [ML] to [ML] often prevents the observation of "reversible" behavior during electrochemical experiments like cyclic voltammetry.  On the forward scan the expected diffusion wave is observed, in example above the reduction of [ML] to [ML].  However on the return scan the corresponding wave is not observed, in the example above this would be the wave corresponding to the oxidation of [ML] to [ML].  In our example there is no [ML] to oxidize since it has been converted to [ML] through ligand loss.  The return wave can sometimes be observed by increasing the scan rates so the following chemical reaction can be observed before the chemical reaction takes place.  This often requires the use of

text: ultramicroelectrode

text: s (UME) capable of very high scan rates of 0.5 to 5.0 V/s.  Plots of forward and reverse peak ratios against modified forms of the scan rate often identify the rate of the chemical reaction.  It has become a common practice to model such plots with electrochemical simulations.  The results of such studies are of disputed practical relevance since simulation requires excellent experimental data, better than that routinely obtained and reported. Furthermore the parameters of such studies are rarely reported and often include an unreasonably high variable to data ratio (ref?).  A better practice is to look for a simple, well documented relationship between observed results and implied phenomena; or to investigate a specific physical phenomenon using an alternative technique such as

text: chronoamperometry

text: or those involving a rotating electrode.

text: These are the solid reactants from which it is proposed to prepare a solid crystalline compound. The selection of reactant chemicals depends on the reaction conditions and expected nature of the product. The reactants are dried thoroughly prior to weighing. As increase in  surface area enhances the reaction rate, fine grained materials should be used if possible.

text: These are the solid reactants from which it is proposed to prepare a solid

text: crystalline

text: compound. The selection of reactant chemicals depends on the reaction conditions and expected nature of the product. The reactants are dried thoroughly prior to weighing. As increase in  surface area enhances the reaction rate, fine grained materials should be used if possible.

text: In the early part of the last century, a parallel concept called Unit Processes was used to classify reactive processes. Thus oxidations, reductions, alkylations, etc. formed separate unit processes and were studied as such. This was natural considering the close affinity of chemical engineering to industrial chemistry at its inception. Gradually however, the subject of chemical reaction engineering has largely replaced the unit process concept. This subject looks at the entire body of chemical reactions as having a personality of its own, independent of the particular chemical species or chemical bonds involved. The latter does contribute to this personality in no small measure, but to design and operate chemical reactors, a knowledge of characteristics such as rate behaviour, thermodynamics, single or multiphase nature, etc. are more important.  The emergence of chemical reaction engineering as a discipline truly signaled the severance of the umbilical cord connecting chemical engineering to industrial chemistry, and served to cement the truly unique character of this discipline.

text: In the early part of the last century, a parallel concept called

text: Unit Processes

text: was used to classify reactive processes. Thus

text: oxidation

text: s,

text: reduction

text: s,

text: alkylation

text: s, etc. formed separate unit processes and were studied as such. This was natural considering the close affinity of chemical engineering to industrial chemistry at its inception. Gradually however, the subject of

text: chemical reaction engineering

text: has largely replaced the unit process concept. This subject looks at the entire body of chemical reactions as having a personality of its own, independent of the particular chemical species or chemical bonds involved. The latter does contribute to this personality in no small measure, but to design and operate chemical reactors, a knowledge of characteristics such as

text: rate behaviour

text: thermodynamics

text: , single or multiphase nature, etc. are more important.  The emergence of chemical reaction engineering as a discipline truly signaled the severance of the umbilical cord connecting chemical engineering to industrial chemistry, and served to cement the truly unique character of this discipline.

text: The katal is not used to express the rate of a reaction; that is expressed in units of concentration per second (or moles per liter per second). Rather, it is used to express catalytic activity which is a property of the catalyst. The katal is invariant of the measurement procedure, but the numerical quantity value is not and depends on the experimental conditions. Therefore, in order to define the quantity of a catalyst, the rate of conversion of a defined chemical reaction is specified as mols reacted per second. One katal of trypsin, for example, is that amount of trypsin which breaks a mole of peptide bonds per second under specified conditions.

text: The katal is not used to express the rate of a reaction; that is expressed in units of concentration per second (or moles per liter per second). Rather, it is used to express catalytic activity which is a property of the catalyst. The katal is invariant of the measurement procedure, but the numerical quantity value is not and depends on the experimental conditions. Therefore, in order to define the quantity of a catalyst, the rate of conversion of a defined chemical reaction is specified as mols reacted per second. One katal of

text: trypsin

text: , for example, is that amount of trypsin which breaks a

text: mole

text: of

text: peptide

text: bonds per second under specified conditions.

text: In enzymology, a rhamnulokinase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , a rhamnulokinase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: When the rate at which polysilicon deposition occurs is slower than the rate at which unreacted silane arrives, then it is said to be surface-reaction-limited. A deposition process that is surface-reaction-limited is primarily dependent on reactant concentration and reaction temperature. Deposition processes must be surface-reaction-limited because they result in excellent thickness uniformity and step coverage. A plot of the logarithm of the deposition rate against the reciprocal of the absolute temperature in the surface-reaction-limited region results in a straight line whose slope is equal to –qE/k.

text: On this basis, many early papers in microwave chemistry postulated the possibility of exciting specific molecules, or functional groups within molecules.  However, the time within which thermal energy is repartitioned from such moieties is much shorter than the period of a microwave wave, thus precluding the presence of such 'molecular hot spots' under ordinary laboratory conditions. The oscillations produced by the radiation in these target molecules would be instantaneously transferred by collisions with the adjacent molecules, reaching at the same moment the thermal equilibrium. Processes with solid phases behave somewhat differently. In this case much higher heat transfer resistances are involved, and the possibility of the stationary presence of hot-spots should be contemplated. A differentiation between two kinds of hot spots has been noted in the literature, although the distinction is considered by many to be arbitrary.  Macroscopic hot spots were considered to comprise all large non-isothermal volumes that can be detected and measured by use of optical pyrometers (optical fibre or IR).  By these means it is possible to visualise thermal inhomogeneities within solid phases under microwave irradiation.  Microscopic hot spots are non-isothermal regions that exist at the micro- or nanoscale (e.g. supported metal nanoparticles inside a catalyst pellet) or in the molecular scale (e.g. a polar group on a catalyst structure).   The distinction has no serious significance, however, as microscopic hotspots such as those proposed to explain catalyst behaviour in several gas-phase catalytic reactions have been demonstrated by post-mortem methods  and in-situ methods. Some theoretical and experimental approaches have been published towards the clarification of the hot spot effect in heterogeneous catalysts.

text: nanoparticles

text: inside a

text: catalyst

text: pellet

text: ) or in the molecular scale (e.g. a polar group on a catalyst structure).   The distinction has no serious significance, however, as microscopic hotspots such as those proposed to explain catalyst behaviour in several gas-phase catalytic reactions have been demonstrated by post-mortem methods  and in-situ methods. Some theoretical and experimental approaches have been published towards the clarification of the hot spot effect in heterogeneous

text: catalysts

text: For physical reasons, it is usually assumed that reactant concentrations cannot be negative, and that each reaction only takes place if all its reactants are present, i.e. all have non-zero concentration. For mathematical reasons, it is usually assumed that

text: The study of catalysis and catalytic reactions is very important to the field of physical organic chemistry. A catalyst participates in the chemical reaction but is not consumed in the process.  A catalyst lowers the activation energy barrier (ΔG), increasing the rate of a reaction by either stabilizing the transition state structure or destabilizing a key reaction intermediate, and as only a small amount of catalyst is required it can provide economic access to otherwise expensive or difficult to synthesize organic molecules. Catalysts may also influence a reaction rate by changing the mechanism of the reaction.

text: The study of

text: catalysis

text: and catalytic reactions is very important to the field of physical organic chemistry. A

text: catalyst

text: participates in the chemical reaction but is not consumed in the process.  A catalyst lowers the

text: activation energy

text: barrier (ΔG), increasing the rate of a reaction by either stabilizing the transition state structure or destabilizing a key reaction intermediate, and as only a small amount of catalyst is required it can provide economic access to otherwise expensive or difficult to synthesize organic molecules. Catalysts may also influence a reaction rate by changing the

text: mechanism

text: of the reaction.

text: In chemical equilibrium the forward and reverse reaction rates are such that each chemical species is being created at the same rate it is being destroyed. In other words, the rate of the forward reaction is equal to the rate of the reverse reaction.

text: In

text: chemical equilibrium

text: the forward and reverse

text: reaction rate

text: s are such that each chemical species is being created at the same rate it is being destroyed. In other words, the rate of the forward reaction is equal to the rate of the reverse reaction.

text: A certain chemical reaction is performed at different temperatures and the reaction rate is determined. The plot of

text: In chemical kinetics, the entropy of activation of a reaction is one of the two parameters (along with the enthalpy of activation) which are typically obtained from the temperature dependence of a reaction rate constant, when these data are analyzed using the Eyring equation. The standard entropy of activation is symbolized ΔS and equals the change in entropy when the reactants change from their initial state to the activated complex or transition state (Δ = change, S = entropy, ‡ = activation). It determines the preexponential factor A of the Arrhenius equation for temperature dependence of reaction rates. The relationship depends on the molecularity of the reaction: for reactions in solution and unimolecular gas reactions  A = (ekT/h) exp(ΔS/R), while for bimolecular gas reactions  A = (ekT/h) (R'T/p) exp(ΔS/R). In these equations e is the base of natural logarithms, h is the Planck constant, k is the Boltzmann constant and T the absolute temperature. R' is the ideal gas constant in units of (bar*L)/(mol*K). The factor is needed because of the pressure dependence of the reaction rate. R' = 8.3145 * 10^-2 (bar*L)/(mol*K).

text: In

text: chemical kinetics

text: , the entropy of activation of a reaction is one of the two parameters (along with the enthalpy of activation) which are typically obtained from the temperature dependence of a reaction

text: rate constant

text: , when these data are analyzed using the

text: Eyring equation

text: . The standard entropy of activation is symbolized ΔS and equals the change in

text: entropy

text: when the reactants change from their initial state to the

text: activated complex

text: or transition state (Δ = change, S = entropy, ‡ = activation). It determines the

text: preexponential factor

text: A of the

text: Arrhenius equation

text: for temperature dependence of reaction rates. The relationship depends on the

text: molecularity

text: of the reaction: for reactions in solution and unimolecular gas reactions  A = (ekT/h) exp(ΔS/R), while for bimolecular gas reactions  A = (ekT/h) (R'T/p) exp(ΔS/R). In these equations e is the base of

text: natural logarithm

text: s, h is the

text: Planck constant

text: , k is the

text: Boltzmann constant

text: and T the

text: absolute temperature

text: . R' is the ideal gas constant in units of (bar*L)/(mol*K). The factor is needed because of the pressure dependence of the reaction rate. R' = 8.3145 * 10^-2 (bar*L)/(mol*K).

text: In chemistry, the law of mass action is the proposition that the rate of a chemical reaction is directly proportional to the product of the activities or concentrations of the reactants. It explains and predicts behaviors of solutions in dynamic equilibrium. Specifically, it implies that for a chemical reaction mixture that is in equilibrium, the ratio between the concentration of reactants and products is constant.

text: In chemistry, the law of mass action is the proposition that the

text: rate

text: of a

text: chemical reaction

text: is directly proportional to the product of the

text: activities

text: or

text: concentrations

text: of the

text: reactants

text: . It explains and predicts behaviors of

text: solutions

text: in

text: dynamic equilibrium

text: . Specifically, it implies that for a chemical reaction mixture that is in equilibrium, the ratio between the concentration of reactants and

text: products

text: is constant.

text: Nanoparticles are desirable in today’s industry for their  high surface area-to-volume ratio in comparison with larger particles of the same elements. Because chemical reactions occur at a rate directly proportional to the available surface area of reactant compounds, nanoparticles can generate reactions at a much faster rate than larger particles of equal mass. Nanoparticles therefore are among the most efficient means of producing reactions and are inherently valuable in the chemical industry. The same property makes them valuable in interactions with molecules.

text: The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which symbolically present the starting materials, end products, and sometimes intermediate products and reaction conditions.

text: The substance (or substances) initially involved in a chemical reaction are called

text: reactants or reagents

text: . Chemical reactions are usually characterized by a

text: chemical change

text: , and they yield one or more

text: products

text: , which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called

text: elementary reaction

text: s, and the information on the precise course of action is part of the

text: reaction mechanism

text: . Chemical reactions are described with

text: chemical equation

text: s, which symbolically present the starting materials, end products, and sometimes intermediate products and reaction conditions.

text: The equilibrium constant of a chemical reaction is the value of the reaction quotient when the reaction has reached equilibrium. An equilibrium constant value is independent of the analytical concentrations of the reactant and product species in a mixture, but depends on temperature and on ionic strength. Known equilibrium constant values can be used to determine the composition of a system at equilibrium.

text: The equilibrium constant of a chemical reaction is the value of the

text: reaction quotient

text: when the reaction has reached

text: equilibrium

text: . An equilibrium constant value is independent of the analytical concentrations of the reactant and product species in a mixture, but depends on temperature and on

text: ionic strength

text: . Known equilibrium constant values can be used to determine the

text: composition of a system at equilibrium

text: Many strategies exist in chemical synthesis that go beyond converting reactant A to reaction product B in a single step. In multistep synthesis, a chemical compound is synthesised though a series of individual chemical reactions, each with their own work-up.  For example, a laboratory synthesis of paracetamol can consist of three individual synthetic steps. In cascade reactions multiple chemical transformations take place within a single reactant, in  multi-component reactions up to 11 different reactants form a single reaction product and in a telescopic synthesis one reactant goes through multiple transformations without isolation of intermediates.

text: Many strategies exist in chemical synthesis that go beyond converting

text: reactant

text: A to reaction product B in a single step. In multistep synthesis, a chemical compound is synthesised though a series of individual chemical reactions, each with their own work-up.  For example, a laboratory synthesis of

text: paracetamol

text: can consist of three individual synthetic steps. In

text: cascade reaction

text: s multiple chemical transformations take place within a single reactant, in

text: multi-component reaction

text: s up to 11 different reactants form a single reaction product and in a

text: telescopic synthesis

text: one reactant goes through multiple transformations without isolation of intermediates.

text: There are many chemical reactions that occur in the catalytic reforming process, all of which occur in the presence of a catalyst and a high partial pressure of hydrogen. Depending upon the type or version of catalytic reforming used as well as the desired reaction severity, the reaction conditions range from temperatures of about 495 to 525 °C and from pressures of about 5 to 45 atm.

text: There are many chemical reactions that occur in the catalytic reforming process, all of which occur in the presence of a catalyst and a high

text: partial pressure

text: of hydrogen. Depending upon the type or version of catalytic reforming used as well as the desired reaction severity, the reaction conditions range from temperatures of about 495 to 525 °C and from pressures of about 5 to 45

text: atm

text: In a chemical reaction, chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time. Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but equal. Thus, there are no net changes in the concentrations of the reactant(s) and product(s). Such a state is known as dynamic equilibrium.

text: In a

text: chemical reaction

text: , chemical equilibrium is the state in which both reactants and products are present in

text: concentration

text: s which have no further tendency to change with time. Usually, this state results when the forward reaction proceeds at the same rate as the

text: reverse reaction

text: . The

text: reaction rate

text: s of the forward and backward reactions are generally not zero, but equal. Thus, there are no net changes in the concentrations of the reactant(s) and product(s). Such a state is known as

text: dynamic equilibrium

text: The main property of the NCL method is the reversibility of the first step, the thiol(ate)–thioester exchange reaction. Native chemical ligation is exquisitely regioselective because that thiol(ate)–thioester exchange step is freely reversible in the presence of an exogenous thiol added as catalyst. The high yields of final ligation product obtained, even in the presence of internal Cys residues in either/both segments, is the result of the irreversibility, under the reaction conditions used, of the second (S-to-N acyl shift) amide-forming step.

text: By convention the products form the numerator.However, the law of mass action is valid only for concerted one-step reactions that proceed through a single transition state and is not valid in general because rate equations do not, in general, follow the stoichiometry of the reaction as Guldberg and Waage had proposed (see, for example, nucleophilic aliphatic substitution by S1 or reaction of hydrogen and bromine to form hydrogen bromide). Equality of forward and backward reaction rates, however, is a necessary condition for chemical equilibrium, though it is not sufficient to explain why equilibrium occurs.

text: By convention the products form the

text: numerator

text: .However, the

text: law of mass action

text: is valid only for concerted one-step reactions that proceed through a single

text: transition state

text: and is not valid in general because

text: rate equations

text: do not, in general, follow the

text: stoichiometry

text: of the reaction as Guldberg and Waage had proposed (see, for example,

text: nucleophilic aliphatic substitution

text: by S1 or reaction of

text: hydrogen

text: and

text: bromine

text: to form

text: hydrogen bromide

text: ). Equality of forward and backward reaction rates, however, is a

text: necessary condition

text: for chemical equilibrium, though it is not

text: sufficient

text: to explain why equilibrium occurs.

text: An electrochemical cell consists of two half-cells. Each half-cell consists of an electrode and an electrolyte. The two half-cells may use the same electrolyte, or they may use different electrolytes. The chemical reactions in the cell may involve the electrolyte, the electrodes, or an external substance (as in fuel cells that may use hydrogen gas as a reactant). In a full electrochemical cell, species from one half-cell lose electrons (oxidation) to their electrode while species from the other half-cell gain electrons (reduction) from their electrode.

text: An electrochemical cell consists of two half-cells. Each half-cell consists of an

text: electrode

text: and an

text: electrolyte

text: . The two half-cells may use the same electrolyte, or they may use different electrolytes. The chemical reactions in the cell may involve the electrolyte, the electrodes, or an external substance (as in

text: fuel cell

text: s that may use hydrogen gas as a reactant). In a full electrochemical cell, species from one half-cell lose electrons (

text: oxidation

text: ) to their

text: electrode

text: while species from the other half-cell gain electrons (

text: reduction

text: ) from their electrode.

text: In chemical kinetics, the overall rate of a reaction is often approximately determined by the slowest step, known as the rate determining step (RDS) or rate-limiting step. For a given reaction mechanism, the prediction of the corresponding rate equation (for comparison with the experimental rate law) is often simplified by using this approximation of the rate determining step.

text: In

text: chemical kinetics

text: , the overall rate of a reaction is often approximately determined by the slowest step, known as the rate determining step (RDS) or rate-limiting step. For a given reaction mechanism, the prediction of the corresponding

text: rate equation

text: (for comparison with the experimental rate law) is often simplified by using this approximation of the rate determining step.

text: The study of chemical kinetics is used to determine the rate law for a reaction. The rate law provides a quantitative relationship between the rate of a chemical reaction and the concentrations or pressures of the chemical species present.  Rate laws must be determined by experimental measurement and generally cannot be elucidated from the chemical equation. The experimentally determined rate law refers to the stoichiometry of the transition state structure relative to the ground state structure. Determination of the rate law was historically accomplished by monitoring the concentration of a reactant during a reaction through gravimetric analysis, but today it is almost exclusively done through fast and unambiguous spectroscopic techniques. In most cases, the determination of rate equations is simplified by adding a large excess (“flooding”) all but one of the reactants.

text: The study of

text: chemical kinetics

text: is used to determine the

text: rate law

text: for a reaction. The rate law provides a quantitative relationship between the rate of a

text: chemical reaction

text: and the

text: concentrations

text: or

text: pressures

text: of the chemical species present.  Rate laws must be determined by experimental measurement and generally cannot be elucidated from the

text: chemical equation

text: . The experimentally determined rate law refers to the stoichiometry of the

text: transition state structure

text: relative to the ground state structure. Determination of the rate law was historically accomplished by monitoring the concentration of a reactant during a reaction through

text: gravimetric analysis

text: , but today it is almost exclusively done through fast and unambiguous

text: spectroscopic

text: techniques. In most cases, the determination of rate equations is simplified by adding a large excess (“flooding”) all but one of the reactants.

text: It is also commonly assumed that no reaction features the same chemical as both a reactant and a product (i.e. no catalysis or autocatalysis), and that increasing the concentration of a reactant increases the rate of any reactions that use it up. This second assumption is compatible with all physically reasonable kinetics, including mass action, Michaelis–Menten and Hill kinetics. Sometimes further assumptions are made about reaction rates, e.g. that all reactions obey mass action kinetics.

text: It is also commonly assumed that no reaction features the same chemical as both a reactant and a product (i.e. no

text: catalysis

text: or

text: autocatalysis

text: ), and that increasing the concentration of a reactant increases the rate of any reactions that use it up. This second assumption is compatible with all physically reasonable kinetics, including

text: mass action

text: Michaelis–Menten

text: and

text: Hill

text: kinetics. Sometimes further assumptions are made about reaction rates, e.g. that all reactions obey mass action kinetics.

text: where V̄ denotes a partial molar volume of a reactant or a product.

text: where V̄ denotes a

text: partial molar volume

text: of a reactant or a product.

text: The PRTase domain is homologous to many other PRTases involved in the purine nucleotide synthesis and salvage pathways. All PRTases involve the displacement of pyrophosphate in PRPP by a variety of nucleophiles. ATase is the only PRTase that has ammonia as a nucleophile. Pyrophosphate from PRPP is an excellent leaving group, so little chemical assistance is needed to promote catalysis. Rather, the primary function of the enzyme appears to be bringing the reactants together appropriately and preventing the wrong reaction, such as hydrolysis.

text: The PRTase domain is homologous to many other PRTases involved in the purine nucleotide synthesis and

text: salvage

text: pathways. All PRTases involve the displacement of pyrophosphate in PRPP by a variety of nucleophiles. ATase is the only PRTase that has ammonia as a nucleophile. Pyrophosphate from PRPP is an excellent leaving group, so little chemical assistance is needed to promote catalysis. Rather, the primary function of the enzyme appears to be bringing the reactants together appropriately and preventing the wrong reaction, such as hydrolysis.

text: In determining the degree at which bioconcentration occurs biological factors have to be kept in mind.The rate at which an organism is exposed through respiratory surfaces and contact with dermal surfaces of the organism, competes against the rate of excretion from an organism. The rate of excretion is a loss of chemical from the respiratory surface, growth dilution, fecal excretion, and metabolic biotransformation. Growth dilution is not an actual process of excretion but due to the mass of the organism increasing while the contaminant concentration remains constant dilution occurs.

text: In determining the degree at which bioconcentration occurs biological factors have to be kept in mind.The rate at which an organism is exposed through respiratory surfaces and contact with dermal surfaces of the organism, competes against the rate of excretion from an organism. The rate of excretion is a loss of chemical from the respiratory surface, growth dilution, fecal excretion, and

text: metabolic biotransformation

text: . Growth dilution is not an actual process of excretion but due to the mass of the organism increasing while the contaminant concentration remains constant dilution occurs.

text: In a chemical reaction, a reactant is considered to be in abundance if the quantity of that substance is high and virtually unchanged by the reaction.  Abundance differs from excess in that a reactant in excess is simply any reactant other than the limiting reagent; the amount by which a reactant is in excess is often specified, such as with terms like "twofold excess", indicating that there is twice the amount of reactant necessary for the limiting reagent to be completely reacted.  In this case, should the reaction go to completion, the quantity of the reactant in excess will have halved.

text: In a

text: chemical reaction

text: , a

text: reactant

text: is considered to be in abundance if the quantity of that substance is high and virtually unchanged by the reaction.  Abundance differs from excess in that a reactant in excess is simply any reactant other than the

text: limiting reagent

text: ; the amount by which a reactant is in excess is often specified, such as with terms like "twofold excess", indicating that there is twice the amount of reactant necessary for the limiting reagent to be completely reacted.  In this case, should the reaction go to completion, the quantity of the reactant in excess will have halved.

text: In enzymology, an oxaloacetase () is an enzyme that catalyzes the chemical reaction:

text: In

text: enzymology

text: , an oxaloacetase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: Other examples of oscillatory systems are certain chemical reactions with multiple steps, some of which involve dynamic equilibria rather than reactions that go to completion. In such cases one can model the rise and fall of reactant and product concentration (or mass, or amount of substance) with the correct differential equations and a good understanding of chemical kinetics.

text: Other examples of oscillatory systems are certain chemical reactions with multiple steps, some of which involve dynamic equilibria rather than reactions that go to completion. In such cases one can model the rise and fall of reactant and product concentration (or mass, or amount of substance) with the correct differential equations and a good understanding of

text: chemical kinetics

text: Chemiluminescence differs from fluorescence or phosphorescence in that the electronic excited state is the product of a chemical reaction rather than of the absorption of a photon.  It is the antithesis of a photochemical reaction, in which light is used to drive an endothermic chemical reaction.  Here, light is generated from a chemically exothermic reaction.

text: Chemiluminescence differs from fluorescence or phosphorescence in that the electronic excited state is the product of a chemical reaction rather than of the

text: absorption of a photon

text: .  It is the antithesis of a

text: photochemical

text: reaction, in which light is used to drive an endothermic chemical reaction.  Here, light is generated from a chemically exothermic reaction.

text: The Heck reaction (also called the Mizoroki-Heck reaction) is the chemical reaction of an unsaturated  halide (or triflate) with an alkene in the presence of a base and a palladium catalyst (or palladium nanomaterial-based catalyst) to form a substituted alkene.  It is named after Tsutomu Mizoroki and Richard F. Heck. Heck was awarded the 2010 Nobel Prize in Chemistry, which he shared with Ei-ichi Negishi and Akira Suzuki, for the discovery and development of this reaction. This reaction was the first example of a carbon-carbon bond-forming reaction that followed a Pd(0)/Pd(II) catalytic cycle, the same catalytic cycle that is seen in other Pd(0)-catalyzed cross-coupling reactions. The Heck reaction is of great importance, as it allows one to do substitution reactions on planar sp-hybridized carbon atoms.

text: The Heck reaction (also called the Mizoroki-Heck reaction) is the

text: chemical reaction

text: of an unsaturated

text: halide

text: (or

text: triflate

text: ) with an

text: alkene

text: in the presence of a

text: base

text: and a

text: palladium catalyst

text: (or palladium

text: nanomaterial-based catalyst

text: ) to form a substituted alkene.  It is named after

text: Tsutomu Mizoroki

text: and

text: Richard F. Heck

text: . Heck was awarded the 2010

text: Nobel Prize in Chemistry

text: , which he shared with

text: Ei-ichi Negishi

text: and

text: Akira Suzuki

text: , for the discovery and development of this reaction. This reaction was the first example of a carbon-carbon bond-forming reaction that followed a Pd(0)/Pd(II) catalytic cycle, the same catalytic cycle that is seen in other Pd(0)-catalyzed

text: cross-coupling reaction

text: s. The Heck reaction is of great importance, as it allows one to do substitution reactions on planar sp-hybridized carbon atoms.

text: In chemistry, stereoselectivity is the property of a chemical reaction in which a single reactant forms an unequal mixture of stereoisomers during the non-stereospecific creation of a new stereocenter or during the non-stereospecific transformation of a pre-existing one. The selectivity arises from differences in steric effects and electronic effects in the mechanistic pathways leading to the different products. Stereoselectivity can vary in degree but it can never be total since the activation energy difference between the two pathways is finite. However, in favorable cases, the minor stereoisomer may not be detectable by the analytic methods used.

text: In

text: chemistry

text: , stereoselectivity is the property of a

text: chemical reaction

text: in which a single

text: reactant

text: forms an unequal mixture of

text: stereoisomers

text: during the

text: non-stereospecific

text: creation of a new

text: stereocenter

text: or during the

text: non-stereospecific

text: transformation of a pre-existing one. The selectivity arises from differences in

text: steric effects

text: and

text: electronic effects

text: in the

text: mechanistic pathways

text: leading to the different products. Stereoselectivity can vary in degree but it can never be total since the activation energy difference between the two pathways is finite. However, in favorable cases, the minor stereoisomer may not be detectable by the analytic methods used.

text: The overall rate constant for the SRL cleavage reaction is second order (k2/K1/2 of 108M-1s-1). This means the reaction rate is directly proportional to the concentrations of the reactant squared. The rate does not appear to be dependent on physical steps, i.e. the two molecules being able to locate each other in solution is not a factor in how quickly they react. This was determined by observing the rate of the reaction under varying viscosities. The dissociation of the products, the separation of the two molecules, also has no effect on the rate. It is suggested that the rate determining step for SRL cleaves occurs within the chemical cleavage of the phosphodiester bond.

text: Pathway 1 is described as an ECECC while pathway 2 would be described as an ECC.  If the catalyst was being considered for solid support pathway 1 which requires a single metal center to function would be a viable candidate.  In contrast a solid support system which separates the individual metal centers would render a catalysts that operates through pathway 2 useless since it requires a step which is second order in metal center.  Determining the reaction mechanism is much like other methods with some techniques unique to electrochemistry.  In most cases electron transfer can be assumed to be much faster than the chemical reactions.  Unlike stoichiometric reactions where the steps between the starting materials and the rate limiting step dominate in catalysis the observed reaction order is usually dominated by the steps between the catalytic resting state and the rate limiting step.

text: Pathway 1 is described as an ECECC while pathway 2 would be described as an ECC.  If the catalyst was being considered for solid support pathway 1 which requires a single metal center to function would be a viable candidate.  In contrast a solid support system which separates the individual metal centers would render a catalysts that operates through pathway 2 useless since it requires a step which is second order in metal center.  Determining the reaction mechanism is much like other methods with some techniques unique to electrochemistry.  In most cases electron transfer can be assumed to be much faster than the chemical reactions.  Unlike

text: stoichiometric

text: reactions where the steps between the starting materials and the

text: rate limiting step

text: dominate in

text: catalysis

text: the observed reaction order is usually dominated by the steps between the catalytic resting state and the rate limiting step.

text: In autocatalysis the catalyst is a product of the overall reaction, in contrast to all other types of catalysis considered in this article. The simplest example of autocatalysis is a reaction of type A + B → 2 B, in one or in several steps. The overall reaction is just A → B, so that B is a product. But since B is also a reactant, it may be present in the rate equation and affect the reaction rate. As the reaction proceeds, the concentration of B increases and can accelerate the reaction as a catalyst. In effect, the reaction accelerates itself or is autocatalyzed.

text: The secondary hydrogen isotope effects or secondary kinetic isotope effect (SKIE) arises in cases where the isotopic substitution is remote from the bond being broken.  The remote atom, nonetheless, influences the internal vibrations of the system that via changes in the zero point energy (ZPE) affect the rates of chemical reactions. Such effects are expressed as ratios of rate for the light isotope to that of the heavy isotope and can be "normal" (ratio is greater than or equal to 1) or "inverse" (ratio is less than 1) effects. SKIE are defined as α,β (etc.) secondary isotope effects where such prefixes refer to the position of the isotopic substitution relative to the reaction center (see alpha and beta carbon). The prefix α refers to the isotope associated with the reaction center while the prefix β refers to the isotope associated with an atom neighboring the reaction center and so on.

text: The secondary hydrogen isotope effects or secondary kinetic isotope effect (SKIE) arises in cases where the isotopic substitution is remote from the bond being broken.  The remote atom, nonetheless, influences the internal vibrations of the system that via changes in the zero point energy (ZPE) affect the rates of chemical reactions. Such effects are expressed as ratios of rate for the light isotope to that of the heavy isotope and can be "normal" (ratio is greater than or equal to 1) or "inverse" (ratio is less than 1) effects. SKIE are defined as α,β (etc.) secondary isotope effects where such prefixes refer to the position of the isotopic substitution relative to the reaction center (see

text: alpha and beta carbon

text: ). The prefix α refers to the isotope associated with the reaction center while the prefix β refers to the isotope associated with an atom neighboring the reaction center and so on.

text: The shuttling of chains back and forth from catalysts via a CSA can be viewed as a competing chemical equilibrium.  Note that the forward and reverse reactions of CSA binding and leaving either Cat1 or Cat2 are possible.  This competition means that a chain can leave Cat1 via a CSA and the reattach to Cat1, polymerizing the same tacticity.  The rate at which the reattachment of Cat1 occurs can be controlled by altering the relative concentrations of Cat1, Cat2 and CSA.  For example, if one wanted to produce a polymer with the properties mainly resulting from the use of Cat1 and only wanted to influence its properties slightly by the presence of Cat2, a greater concentration of Cat1 would be used than for Cat2.  The rate of alternation between tacticity can be controlled by altering the concentration of CSA relative to Cat1 and Cat2; having a higher concentration of CSA means that the chains will shuttle back and forth more rapidly, creating shorter units of alternating tacticity.

text: The shuttling of chains back and forth from catalysts via a CSA can be viewed as a competing

text: chemical equilibrium

text: .  Note that the forward and reverse reactions of CSA binding and leaving either Cat1 or Cat2 are possible.  This competition means that a chain can leave Cat1 via a CSA and the reattach to Cat1, polymerizing the same tacticity.  The

text: rate

text: at which the reattachment of Cat1 occurs can be controlled by altering the relative concentrations of Cat1, Cat2 and CSA.  For example, if one wanted to produce a polymer with the properties mainly resulting from the use of Cat1 and only wanted to influence its properties slightly by the presence of Cat2, a greater concentration of Cat1 would be used than for Cat2.  The rate of alternation between tacticity can be controlled by altering the concentration of CSA relative to Cat1 and Cat2; having a higher concentration of CSA means that the chains will shuttle back and forth more rapidly, creating shorter units of alternating tacticity.

text: symbol signifies that this is the transition state in a chemical reaction. The rate of this reaction is proportional to the concentration of the aqua ion, [A].

text: symbol signifies that this is the

text: transition state

text: in a chemical reaction. The rate of this reaction is proportional to the concentration of the aqua ion, [A].

text: Transition state theory (TST) explains the reaction rates of elementary chemical reactions. The theory assumes a special type of chemical equilibrium (quasi-equilibrium) between reactants and activated transition state complexes.

text: Transition state theory (TST) explains the

text: reaction rate

text: s of elementary

text: chemical reaction

text: s. The theory assumes a special type of

text: chemical equilibrium

text: (quasi-equilibrium) between

text: reactant

text: s and activated

text: transition state

text: complexes.

text: Catalytic oxidizer (also known as catalytic incinerator) is another category of oxidation systems that is similar to typical thermal oxidizers, but the catalytic oxidizers use a catalyst to promote the oxidation. Catalytic oxidation occurs through a chemical reaction between the VOC hydrocarbon molecules and a precious-metal catalyst bed that is internal to the oxidizer system. A catalyst is a substance that is used to accelerate the rate of a chemical reaction, allowing the reaction to occur in a normal temperature range between  and .

text: Catalytic oxidizer (also known as catalytic incinerator) is another category of oxidation systems that is similar to typical thermal oxidizers, but the catalytic oxidizers use a

text: catalyst

text: to promote the oxidation. Catalytic oxidation occurs through a chemical reaction between the VOC hydrocarbon molecules and a precious-metal catalyst bed that is internal to the oxidizer system. A catalyst is a substance that is used to accelerate the rate of a chemical reaction, allowing the reaction to occur in a normal temperature range between  and .

text: In chemical engineering and reactor engineering, space velocity refers to the quotient of the entering volumetric flow rate of the reactants divided by the reactor volume (or the catalyst bed volume) which indicates how many reactor volumes of feed can be treated in a unit time (for instance, a reactor with a space velocity of 7 h is able to process feed equivalent to seven times the reactor volume each hour). It is commonly regarded as the reciprocal of the reactor space time. In industry, space velocity can be further defined by the phase of the reactants at given conditions. Special values for this measurement exist for liquids and gases, and for systems that use solid catalysts.

text: In

text: chemical engineering

text: and

text: reactor engineering

text: , space velocity refers to the quotient of the entering

text: volumetric flow rate

text: of the

text: reactant

text: s divided by the

text: reactor

text: volume (or the

text: catalyst

text: bed volume) which indicates how many reactor volumes of feed can be treated in a unit time (for instance, a reactor with a space velocity of 7 h is able to process feed equivalent to seven times the reactor volume each hour). It is commonly regarded as the

text: reciprocal

text: of the reactor

text: space time

text: . In industry, space velocity can be further defined by the phase of the reactants at given conditions. Special values for this measurement exist for liquids and gases, and for systems that use solid catalysts.

text: The concepts of Lewis acid-base theory and Brønsted-Lowry acid-base theory may be applied to surfaces, however there is no general theory that serves to determine surface acidity or basicity. The qualitative treatment of Brønsted acid base theory is based on the thermodynamic equilibrium constant (K) of acid-base reactions between individual molecules in homogeneous systems. This treatment requires measurement of equilibrium concentrations of reactants and products. The presence of two phases also provides a problem for the quantitative acid-base determination of solids. When an acid or base is adsorbed on to an oxide surface it will perturb neighbouring acid-base sites. This perturbation will inevitably influence the relaxation of the surface and make it impossible to have acid-base reactions at the surface which only involve a single surface site.

text: The concepts of

text: Lewis acid-base theory

text: and

text: Brønsted-Lowry acid-base theory

text: may be applied to surfaces, however there is no general theory that serves to determine surface acidity or basicity. The qualitative treatment of Brønsted acid base theory is based on the thermodynamic

text: equilibrium constant

text: (K) of acid-base reactions between individual molecules in homogeneous systems. This treatment requires measurement of equilibrium concentrations of reactants and products. The presence of two phases also provides a problem for the quantitative acid-base determination of solids. When an acid or base is adsorbed on to an oxide surface it will perturb neighbouring acid-base sites. This perturbation will inevitably influence the

text: relaxation

text: of the surface and make it impossible to have acid-base reactions at the surface which only involve a single surface site.

text: Although the presence of an allylic alcohol does lead to increased stereoselectivity, the rates of these reactions are slower than systems lacking alcohols. However, the reaction rates of substrates with a hydrogen bonding group are still faster than the equivalent protected substrates. This observation is attributed to a balance of two factors. The first is the stabilization of the transition state as a result of the hydrogen bonding. The second is the electron withdrawing nature of the oxygen, which draws electron density away from the alkene, lowering its reactivity.

text: The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. A chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. Many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. Reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. Many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like the Woodward–Hoffmann rules often come in handy while proposing a mechanism for a chemical reaction.

text: The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its

text: mechanism

text: . A chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. Many

text: reaction intermediates

text: with variable stability can thus be envisaged during the course of a reaction. Reaction mechanisms are proposed to explain the

text: kinetics

text: and the relative product mix of a reaction. Many

text: physical chemists

text: specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like the

text: Woodward–Hoffmann rules

text: often come in handy while proposing a mechanism for a chemical reaction.

text: However NO is an unstable intermediate whose concentration is determined by the fact that the first step is in equilibrium, so that , where K is the equilibrium constant of the first step. Substitution of this equation in the previous equation leads to a rate equation expressed in terms of the original reactants

text: However NO is an unstable intermediate whose concentration is determined by the fact that the first step is in

text: equilibrium

text: , so that , where K is the

text: equilibrium constant

text: of the first step. Substitution of this equation in the previous equation leads to a rate equation expressed in terms of the original reactants

text: Chemical kinetics, also known as reaction kinetics, is the study of rates of chemical processes. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition states, as well as the construction of mathematical models that can describe the characteristics of a chemical reaction.

text: Chemical kinetics, also known as reaction kinetics, is the study of

text: rates

text: of

text: chemical process

text: es. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a

text: chemical reaction

text: and yield information about the

text: reaction's mechanism

text: and

text: transition state

text: s, as well as the construction of

text: mathematical model

text: s that can describe the characteristics of a chemical reaction.

text: Homogeneous reactions are chemical reactions in which the reactants and products are in the same phase, while heterogeneous reactions have reactants in two or more phases. Reactions that take place on the surface of a catalyst of a different phase are also heterogeneous. A reaction between two gases or two miscible liquids is homogeneous. A reaction between a gas and a liquid, a gas and a solid or a liquid and a solid is heterogeneous.

text: Homogeneous reactions are

text: chemical reaction

text: s in which the reactants and products are in the same

text: phase

text: , while heterogeneous reactions have

text: reactant

text: s in two or more phases. Reactions that take place on the surface of a catalyst of a different phase are also heterogeneous. A reaction between two gases or two miscible liquids is homogeneous. A reaction between a gas and a liquid, a gas and a solid or a liquid and a solid is heterogeneous.

text: The SSA is physically accurate only for systems that are both dilute and well-mixed in the reactant (solute) molecules.  An extension of the SSA which is aimed at circumventing the globally well-mixed requirement is the reaction-diffusion SSA (RD-SSA).  It subdivides the system volume into cubic subvolumes or “voxels” which are small enough that each can be considered well-mixed.  Chemical reactions are then considered to occur inside individual voxels and are modeled using the SSA.  The diffusion of reactant molecules to adjacent voxels is modeled by special “voxel-hopping” reactions that accurately simulate the diffusion equation provided the voxels are, again, sufficiently small.  But modeling a bimolecular reaction inside a voxel using the SSA’s reaction probability rate will be physically valid only if the reactant molecules are dilute inside the voxel, and that requires the voxels to be much larger than the reactant molecules.  These opposing requirements (smaller vs. larger) on the voxel size for the RD-SSA often cannot be simultaneously met.  In such cases, it will be necessary to adopt a much less restrictive simulation strategy that carefully tracks the location of every reactant molecule in the system.  An algorithm of that kind was devised in 2014 by Gillespie and co-workers.  Called the small-voxel tracking algorithm (SVTA), it subdivides the system volume into voxels that are smaller than the reactant molecules, and hence much smaller than the voxels used in the RD-SSA.  Diffusion is therefore modeled much more accurately in the SVTA than in the RD-SSA.  But inside such small voxels, the SSA’s bimolecular reaction probability rate will no longer be physically valid.  So the SVTA instead models bimolecular reactions using a novel extension of the diffusional voxel-hopping rule. That extension rectifies the physical incorrectness of the standard diffusion equation on the small space-time scales where collision-induced reactions occur.  The SVTA thus eliminates the requirements that the system be dilute and well-mixed, and it does so in a way that has theoretical support in molecular physics.  The price for this major gain in robustness and accuracy is a simulation procedure that is more computationally intensive.  Details of the SVTA and its justification in physical theory are given in the original paper; however, that paper does not develop a widely applicable, user-friendly software implementation of the SVTA.

text: For a reaction between reactants A and B to form product C

text: Unlike many other functions of state, entropy cannot be directly observed but must be calculated. Entropy can be calculated for a substance as the standard molar entropy from absolute zero (also known as absolute entropy) or as a difference in entropy from some other reference state which is defined as zero entropy. Entropy has the dimension of energy divided by temperature, which has a unit of joules per kelvin (J/K) in the International System of Units. While these are the same units as heat capacity, the two concepts are distinct. Entropy is not a conserved quantity: for example, in an isolated system with non-uniform temperature, heat might irreversibly flow and the temperature become more uniform such that entropy increases. The second law of thermodynamics states that a closed system has entropy which may increase or otherwise remain constant. Chemical reactions cause changes in entropy and entropy plays an important role in determining in which direction a chemical reaction spontaneously proceeds.

text: Unlike many other functions of state, entropy cannot be directly observed but must be calculated. Entropy can be calculated for a substance as the

text: standard molar entropy

text: from

text: absolute zero

text: (also known as absolute entropy) or as a difference in entropy from some other reference state which is defined as zero entropy. Entropy has the

text: dimension

text: of

text: energy

text: divided by

text: temperature

text: , which has a unit of

text: joule

text: s per

text: kelvin

text: (J/K) in the

text: International System of Units

text: . While these are the same units as

text: heat capacity

text: , the two concepts are distinct. Entropy is not a conserved quantity: for example, in an isolated system with non-uniform temperature, heat might irreversibly flow and the temperature become more uniform such that entropy increases. The

text: second law of thermodynamics

text: states that a closed system has entropy which may increase or otherwise remain constant. Chemical reactions cause changes in entropy and entropy plays an important role in determining in which direction a chemical reaction spontaneously proceeds.

text: For example, if  [A] is luminol and [B] is hydrogen peroxide in the presence of a suitable catalyst we have:

text: For example, if  [A] is

text: luminol

text: and [B] is

text: hydrogen peroxide

text: in the presence of a suitable catalyst we have:

text: The products of a chemical reaction influence several aspects of the reaction. If the products are lower in energy than the reactants, then the reaction will give off excess energy making it an exergonic reaction. Such reactions are thermodynamically favorable and tend to happen on their own. If the kinetics of the reaction are high enough, however, then the reaction may occur too slowly to be observed, or not even occur at all. This is the case with the conversion of diamond to lower energy graphite at atmospheric pressure, in such a reaction diamond is considered metastable and will not be observed converting into graphite.

text: The products of a chemical reaction influence several aspects of the reaction. If the products are lower in energy than the reactants, then the reaction will give off excess energy making it an

text: exergonic reaction

text: . Such reactions are thermodynamically favorable and tend to happen on their own. If the

text: kinetics

text: of the reaction are high enough, however, then the reaction may occur too slowly to be observed, or not even occur at all. This is the case with the conversion of diamond to lower energy graphite at atmospheric pressure, in such a reaction diamond is considered

text: metastable

text: and will not be observed converting into graphite.

text: The heat transfer rate of smokeless propellants increases with pressure; so the rate of gas generation from a given grain surface area increases at higher pressures. Accelerating gas generation from fast burning propellants may rapidly create a destructively high pressure spike before bullet movement increases reaction volume. Conversely, propellants designed for a minimum heat transfer pressure may cease decomposition into gaseous reactants if bullet movement decreases pressure before a slow burning propellant has been consumed. Unburned propellant grains may remain in the barrel if the energy-releasing flame zone cannot be sustained in the resultant absence of gaseous reactants from the inner zones.

text: The concentrations of individual compounds can be derived largely using the count rates of the precursor and product ions, and the reaction rate coefficients, k. Exothermic proton transfer reactions with HO are assumed to proceed at the collisional rate (see Collision Theory), the coefficient for which, k, is calculable using the method described by Su and Chesnavich, providing the polarizability and dipole moment are known for the reactant molecule. NO and O reactions proceed at k less frequently, and thus the reaction rates of the reactant molecule with these precursor ions must often be derived experimentally by comparing the decline in the count rates of each of the NO and O precursor ions to that of HO as the sample flow of reactant molecules is increased. The product ions and rate coefficients have been derived in this way for well over 200 volatile compounds, which can be found in the scientific literature.

text: The concentrations of individual compounds can be derived largely using the count rates of the precursor and product ions, and the

text: reaction rate coefficients

text: , k.

text: Exothermic

text: proton transfer reactions with HO are assumed to proceed at the collisional rate (see

text: Collision Theory

text: ), the coefficient for which, k, is calculable using the method described by Su and Chesnavich, providing the

text: polarizability

text: and

text: dipole moment

text: are known for the reactant molecule. NO and O reactions proceed at k less frequently, and thus the reaction rates of the reactant molecule with these precursor ions must often be derived experimentally by comparing the decline in the count rates of each of the NO and O precursor ions to that of HO as the sample flow of reactant molecules is increased. The product ions and rate coefficients have been derived in this way for well over 200 volatile compounds, which can be found in the scientific literature.

text: Temporal Analysis of Products (TAP), (TAP-2), (TAP-3) is an experimental technique for studyingthe kinetics of physico-chemical interactions between gases and complex solid materials, primarily heterogeneous catalysts. The TAP methodology is based on short pulse-response experiments at low background pressure (10-10 Pa), which are used to probe different steps in a catalytic process on the surface of a porous material including diffusion, adsorption, surface reactions, and desorption.

text: Temporal Analysis of Products (TAP), (TAP-2), (TAP-3) is an experimental technique for studyingthe

text: kinetics

text: of

text: physico-chemical

text: interactions between gases and complex solid materials, primarily

text: heterogeneous catalysts

text: . The TAP methodology is based on short pulse-response experiments at low background pressure (10-10 Pa), which are used to probe different steps in a

text: catalytic process

text: on the surface of a

text: porous material

text: including

text: diffusion

text: adsorption

text: surface reactions

text: , and

text: desorption

text: Combination reactions can involve different types of reactants:

text: Many problems in molecular reaction dynamics demand the simultaneous measurement of a particle's speed and angular direction; the most demanding require the measurement of this velocity in coincidence with internal energy. Studies of molecular reactions, energy transfer processes and photodissociation can only be understood completely if the internal energies and velocities of all products can be specified.Product imaging approaches this goal by determining the three-dimensional velocity distribution of one state-selected product of the reaction.  For a reaction producing two products, because the speed of the unobserved sibling product is related to that of the measured product through conservation of momentum and energy, the internal state of the sibling can often be inferred.

text: Many problems in molecular

text: reaction dynamics

text: demand the simultaneous measurement of a particle's speed and angular direction; the most demanding require the measurement of this velocity in coincidence with internal energy. Studies of molecular reactions, energy transfer processes and photodissociation can only be understood completely if the internal energies and velocities of all products can be specified.Product imaging approaches this goal by determining the three-dimensional velocity distribution of one state-selected product of the reaction.  For a reaction producing two products, because the speed of the unobserved sibling product is related to that of the measured product through conservation of momentum and energy, the internal state of the sibling can often be inferred.

text: The first step in the WGS reaction is the high temperature shift which is carried out at temperatures between 320 °C and 450 °C. As mentioned before, the catalyst is a composition of iron-oxide, FeO(90-95%), and chromium oxides CrO (5-10%) which have an ideal activity and selectivity at these temperatures. When preparing this catalyst, one of the most important step is washing to remove sulfate that can turn into hydrogen sulfide and poison the LTS catalyst later in the process.  Chromium is added to the catalyst to stabilize the catalyst activity over time and to delay sintering of iron oxide. Sintering will decrease the active catalyst area, so by decreasing the sintering rate the lifetime of the catalyst will be extended. The catalyst is usually used in pellets form, and the size play an important role. Large pellets will be strong, but the reaction rate will be limited.

text: The first step in the WGS reaction is the high temperature shift which is carried out at temperatures between 320 °C and 450 °C. As mentioned before, the catalyst is a composition of iron-oxide, FeO(90-95%), and chromium oxides CrO (5-10%) which have an ideal activity and selectivity at these temperatures. When preparing this catalyst, one of the most important step is washing to remove sulfate that can turn into hydrogen sulfide and poison the LTS catalyst later in the process.  Chromium is added to the catalyst to stabilize the catalyst activity over time and to delay

text: sintering

text: of iron oxide. Sintering will decrease the active catalyst area, so by decreasing the sintering rate the lifetime of the catalyst will be extended. The catalyst is usually used in pellets form, and the size play an important role. Large pellets will be strong, but the reaction rate will be limited.

text: According to the Le Chatelier's principle, a lower temperature should be used to shift the chemical equilibrium towards the right, hence increasing the percentage yield. However too low of a temperature will lower the formation rate to an uneconomical level. Hence to increase the reaction rate, high temperatures (450 °C), medium pressures (1-2 atm), and vanadium(V) oxide (VO) are used to ensure a adequate (>95%) conversion. The catalyst only serves to increase the rate of reaction as it does not change the position of the thermodynamic equilibrium. The mechanism for the action of the catalyst comprises two steps:

text: According to the

text: Le Chatelier's principle

text: , a lower temperature should be used to shift the chemical equilibrium towards the right, hence increasing the percentage yield. However too low of a temperature will lower the formation rate to an uneconomical level. Hence to increase the reaction rate, high temperatures (450 °C), medium pressures (1-2

text: atm

text: ), and

text: vanadium(V) oxide

text: (VO) are used to ensure a adequate (>95%) conversion. The catalyst only serves to increase the rate of reaction as it does not change the position of the

text: thermodynamic equilibrium

text: . The mechanism for the action of the catalyst comprises two steps:

text: Most chemical reactions are reversible, that is they can and do run in both directions. The forward and reverse reactions are competing with each other and differ in reaction rates. These rates depend on the concentration and therefore change with time of the reaction: the reverse rate gradually increases and becomes equal to the rate of the forward reaction, establishing the so-called chemical equilibrium. The time to reach equilibrium depends on such parameters as temperature, pressure and the materials involved, and is determined by the minimum free energy. In equilibrium, the Gibbs free energy must be zero. The pressure dependence can be explained with the Le Chatelier's principle. For example, an increase in pressure due to decreasing volume causes the reaction to shift to the side with the fewer moles of gas.

text: Most chemical reactions are reversible, that is they can and do run in both directions. The forward and reverse reactions are competing with each other and differ in

text: reaction rates

text: . These rates depend on the concentration and therefore change with time of the reaction: the reverse rate gradually increases and becomes equal to the rate of the forward reaction, establishing the so-called chemical equilibrium. The time to reach equilibrium depends on such parameters as temperature, pressure and the materials involved, and is determined by the

text: minimum free energy

text: . In equilibrium, the

text: Gibbs free energy

text: must be zero. The pressure dependence can be explained with the

text: Le Chatelier's principle

text: . For example, an increase in pressure due to decreasing volume causes the reaction to shift to the side with the fewer moles of gas.

text: Reaction rates may also be defined on a basis that is not the volume of the reactor.  When a catalyst is used the reaction rate may be stated on a catalyst weight (mol g s) or surface area (mol m s) basis.  If the basis is a specific catalyst site that may be rigorously counted by a specified method, the rate is given in units of s and is called a turnover frequency.

text: Reaction rates may also be defined on a basis that is not the volume of the reactor.  When a

text: catalyst

text: is used the reaction rate may be stated on a catalyst weight (mol g s) or surface area (mol m s) basis.  If the basis is a specific catalyst site that may be rigorously counted by a specified method, the rate is given in units of s and is called a turnover frequency.

text: There are many ways to chemically synthesize glycosidic bonds. Fischer glycosidation refers to the synthesis of glycosides by the reaction of unprotected monosaccharides with alcohols (usually as solvent) in the presence of a strong acid catalyst. The Koenigs-Knorr reaction is the condensation of glycosyl halides and alcohols in the presence of metal salts such as silver carbonate or mercuric oxide.

text: There are many ways to chemically synthesize glycosidic bonds.

text: Fischer glycosidation

text: refers to the synthesis of glycosides by the reaction of unprotected monosaccharides with alcohols (usually as solvent) in the presence of a strong acid catalyst. The

text: Koenigs-Knorr reaction

text: is the condensation of glycosyl halides and alcohols in the presence of metal salts such as silver carbonate or mercuric oxide.

text: There is no specific number of reactants in a combination reaction.

text: As a catalyst is regenerated in a reaction, often only small amounts are needed to increase the rate of the reaction. In practice, however, catalysts are sometimes consumed in secondary processes.

text: In practice, almost all chemical compounds and materials are subject to biodegradation, the key is the relative rates of such processes - minutes, days, years, centuries...  A number of factors determine the degradation rate of organic compounds. Salient factors include light, water and oxygen. Temperature is also important because chemical reactions proceed more quickly at higher temperatures. The degradation rate of many organic compounds is limited by their bioavailability.  Compounds must be released into solution before organisms can degrade them.

text: The temperature achieved in the reaction in adiabatic conditions, when no heat is lost to the environment, can be estimated using the Hess's law – by calculating the energy produced by the reaction itself (subtracting the enthalpy of the reactants from the enthalpy of the products) and subtracting the energy consumed to heating the products (from their specific heat, when the materials only change their temperature, and their enthalpy of fusion and eventually enthalpy of vaporization, when the materials melt or boil). In real conditions, the reaction loses heat to the environment, the achieved temperature is therefore somewhat lower. The heat transfer rate is finite, so the faster the reaction is, the closer to adiabatic condition it runs and the higher is the achieved temperature.

text: The temperature achieved in the reaction in

text: adiabatic conditions

text: , when no heat is lost to the environment, can be estimated using the

text: Hess's law

text: – by calculating the energy produced by the reaction itself (subtracting the enthalpy of the reactants from the enthalpy of the products) and subtracting the energy consumed to heating the products (from their specific heat, when the materials only change their temperature, and their

text: enthalpy of fusion

text: and eventually

text: enthalpy of vaporization

text: , when the materials melt or boil). In real conditions, the reaction loses heat to the environment, the achieved temperature is therefore somewhat lower. The heat transfer rate is finite, so the faster the reaction is, the closer to adiabatic condition it runs and the higher is the achieved temperature.

text: The reaction is usually initiated by copper(II) chloride (CuCl), which is the most common catalyst in the production of 1,2-dichloroethane. In some cases, CuCl is supported on silica in presence of KCl, LaCl, or AlCl as cocatalysts. Aside from silica, a variety of supports have also been used including various types of alumina, diatomaceous earth, or pumice. Because this reaction is highly exothermic (238 kJ/mol), the temperature is monitored, to guard against thermal degradation of the catalyst.  The reaction is as follows:

text: The reaction is usually initiated by

text: copper(II) chloride

text: (CuCl), which is the most common catalyst in the production of

text: . In some cases, CuCl is

text: supported

text: on silica in presence of KCl, LaCl, or AlCl as cocatalysts. Aside from silica, a variety of supports have also been used including various types of

text: alumina

text: diatomaceous earth

text: , or

text: pumice

text: . Because this reaction is highly exothermic (238 kJ/mol), the temperature is monitored, to guard against thermal degradation of the catalyst.  The reaction is as follows:

text: is the reaction rate per volume of catalyst,

text: is the

text: reaction rate

text: per volume of catalyst,

text: There exist several ways to coat the inner surface with specific charges. Diffusion-limited patterning can be utilized because a bulk solution only penetrate the entrance of a nanochannel within a certain distance. Because the diffusion speed is different for each reactant. By introducing several steps of reactants flowing into the nanochannel, it is possible to pattern the surface with different surface charges inside the channel.

text: The intrinsic reaction co-ordinate (IRC), derived from the potential energy surface, is a parametric curve that connects two energy minima in the direction that traverses the minimum energy barrier (or shallowest ascent) passing through one or more saddle point(s). However, in reality if reacting species attains enough energy it may deviate from the IRC to some extent. The energy values (points on the hyper-surface) along the reaction coordinate result in a 1-D energy surface (a line) and when plotted against the reaction co-ordinate (energy vs reaction coordinate) gives what is called a reaction co-ordinate diagram (or energy profile). Another way of visualizing an energy profile is as a cross section of the hyper surface, or surface, long the reaction co-ordinate. Figure 5 shows an example of a cross section, represented by the plane, taken along the reaction coordinate and the potential energy is represented as a function or composite of two geometric variables  to form a 2-D energy surface. In principle, the potential energy function can depend on N variables but since an accurate visual representation of  a function of 3 or more variables cannot be produced (excluding level hypersurfaces) a 2-D surface has been shown. The points on the surface that intersect the plane are then projected onto the reaction coordinate diagram (shown on the right) to produce a 1-D slice of the surface along the IRC. The reaction coordinate is described by its parameters, which are frequently given as a composite of several geometric parameters, and can change direction as the reaction progresses so long as the smallest energy barrier (or activation energy (Ea)) is traversed. The saddle point represents the highest energy point lying on the reaction coordinate connecting the reactant and product; this is known as the transition state. A reaction co-ordinate diagram may also have one or more transient intermediates which are shown by high energy wells connected via a transition state peak. Any chemical structure that lasts longer than the time for typical bond vibrations (10 – 10s) can be considered as intermediate.

text: level hypersurfaces

text: ) a 2-D surface has been shown. The points on the surface that intersect the plane are then projected onto the reaction coordinate diagram (shown on the right) to produce a 1-D slice of the surface along the IRC. The reaction coordinate is described by its parameters, which are frequently given as a composite of several geometric parameters, and can change direction as the reaction progresses so long as the smallest energy barrier (or activation energy (Ea)) is traversed. The saddle point represents the highest energy point lying on the reaction coordinate connecting the reactant and product; this is known as the transition state. A reaction co-ordinate diagram may also have one or more transient intermediates which are shown by high energy wells connected via a transition state peak. Any chemical structure that lasts longer than the time for typical bond vibrations (10 – 10s) can be considered as intermediate.

text: , appear as factors with optional exponents associated with each. Other factors and terms not appearing in the equation, can be added to include effects such as the presence of non-reactingspecies in the rate equation. Such so-called third-body reactions are typical of the effect of a catalyst on a reaction, for example. Many of the factors are often collected into a single rate constant,

text: The relative stability of reactant and product does not define the feasibility of any reaction all by itself. For any reaction to proceed, the starting material must have enough energy to cross over an energy barrier. This energy barrier is known as activation energy (∆G) and the rate of reaction is dependent on the height of this barrier. A low energy barrier corresponds to a fast reaction and high energy barrier corresponds to a slow reaction.A reaction is in equilibrium when the rate of forward reaction is equal to the rate of reverse reaction. Such a reaction is said to be reversible. In principle, all the reactions are reversible but in some cases the equilibrium lies so much towards the product side that it is impossible to see the starting material. Usually, a reaction with equilibrium constant  10 is termed as irreversible. If the starting material and product(s) are in equilibrium then their relative abundance is decided by the difference in free energy between them.

text: The eddy dissipation model, based on the work of Magnussen and Hjertager is a turbulent-chemistry reaction model. Most fuels are fast burning and the overall rate of reaction is controlled by turbulence mixing. In the non-premixed flames, turbulence slowly mixes the fuel and oxidizer into the reaction zones where they burn quickly. In premixed flames the turbulence slowly mixes cold reactants and hot products into the reaction zones where reaction occurs rapidly. In such cases the combustion is said to be mixing-limited, and the complex and often unknown chemical kinetics can be safely neglected. In this model, the chemical reaction is governed by large eddy mixing time scale. Combustion initiates whenever there is turbulence present in the flow. It does not need an ignition source to initiate the combustion. It is good for the non-premixed combustion but for the premixed flames the reactant will burn at the moment they enter in the computation model, which is incorrect. The reactant need some time to get to the ignition temperature to initiate the combustion. It is a shortcoming of this model.

text: The eddy dissipation model, based on the work of Magnussen and Hjertager is a turbulent-chemistry reaction model. Most fuels are fast burning and the overall rate of reaction is controlled by turbulence mixing. In the non-premixed flames, turbulence slowly mixes the fuel and oxidizer into the reaction zones where they burn quickly. In premixed flames the turbulence slowly mixes cold reactants and hot products into the reaction zones where reaction occurs rapidly. In such cases the combustion is said to be mixing-limited, and the complex and often unknown chemical kinetics can be safely neglected. In this model, the chemical reaction is governed by large eddy mixing time scale. Combustion initiates whenever there is turbulence present in the flow. It does not need an ignition source to initiate the combustion. It is good for the non-premixed combustion but for the premixed flames the reactant will burn at the moment they enter in the

text: computation model

text: , which is incorrect. The reactant need some time to get to the ignition temperature to initiate the combustion. It is a shortcoming of this model.

text: In a platinum-based silicone cure system, also called an addition system (because the key reaction building polymer is an "Addition reaction"). With platinum as catalyst, two different chemical groups react, a silicone hydride and a vinyl. In this reaction, an ethyl group [C(H2)- C(H2)] is formed and there are no byproducts. Two separate components must be mixed to catalyze the polymers: the one component contains a platinum complex which must be mixed with the second, a hydride- and a vinyl-functional siloxane polymer, creating an ethyl bridge between the two.  Such silicone rubbers cure quickly, though the rate of or even ability to cure is easily inhibited in the presence of elemental tin, sulphur, and many amine compounds.

text: In a platinum-based silicone cure system, also called an addition system (because the key reaction building polymer is an "Addition reaction"). With platinum as catalyst, two different chemical groups react, a silicone hydride and a vinyl. In this reaction, an ethyl group [C(H2)- C(H2)] is formed and there are no byproducts. Two separate components must be mixed to catalyze the polymers: the one component contains a platinum

text: complex

text: which must be mixed with the second, a

text: hydride

text: - and a

text: vinyl

text: -functional

text: siloxane

text: polymer, creating an

text: ethyl

text: bridge between the two.  Such silicone rubbers cure quickly, though the rate of or even ability to cure is easily inhibited in the presence of elemental

text: tin

text: sulphur

text: , and many

text: amine

text: compounds.

text: Chemical reactions happen at a characteristic reaction rate at a given temperature and chemical concentration. Typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms.

text: Chemical reactions happen at a characteristic

text: reaction rate

text: at a given temperature and chemical concentration. Typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms.

text: This process has been demonstrated with dicyclopentadiene (DCPD) and Grubbs' catalyst (benzylidene-bis(tricyclohexylphosphine)dichlororuthenium). Both DCPD and Grubbs' catalyst are imbedded in an epoxy resin. The monomer on its own is relatively unreactive and polymerization does not take place. When a microcrack reaches both the capsule containing DCPD and the catalyst, the monomer is released from the core–shell microcapsule and comes in contact with exposed catalyst, upon which the monomer undergoes ring opening metathesis polymerization (ROMP). The metathesis reaction of the monomer involves the severance of the two double bonds in favor of new bonds.  The presence of the catalyst allows for the energy barrier (energy of activation) to be lowered, and the polymerization reaction can proceed at room temperature. The resulting polymer allows the epoxy composite material to regain 67% of its former strength.

text: This process has been demonstrated with

text: dicyclopentadiene

text: (DCPD) and

text: Grubbs' catalyst

text: (benzylidene-bis(tricyclohexylphosphine)dichlororuthenium). Both DCPD and

text: Grubbs' catalyst

text: are imbedded in an

text: epoxy

text: resin

text: . The

text: monomer

text: on its own is relatively unreactive and

text: polymerization

text: does not take place. When a microcrack reaches both the capsule containing DCPD and the

text: catalyst

text: , the

text: monomer

text: is released from the core–shell microcapsule and comes in contact with exposed catalyst, upon which the monomer undergoes

text: ring opening metathesis polymerization

text: (ROMP). The

text: metathesis

text: reaction of the

text: monomer

text: involves the severance of the two double bonds in favor of new bonds.  The presence of the

text: catalyst

text: allows for the

text: energy barrier

text: (energy of activation) to be lowered, and the polymerization

text: reaction

text: can proceed at room temperature. The resulting

text: polymer

text: allows the

text: epoxy

text: composite material

text: to regain 67% of its former strength.

text: Speed of processing refers to the maximum speed at which a given mental act may be efficiently executed. It is measured in reference to the reaction time to very simple tasks, such as the time needed to recognize an object.

text: Speed of processing refers to the maximum speed at which a given mental act may be efficiently executed. It is measured in reference to the

text: reaction time

text: to very simple tasks, such as the time needed to recognize an object.

text: Statistical copolymers are dictated by the reaction kinetics of the two chemically distinct monomer reactants, and are commonly referred to interchangeably as “random” in the polymer literature. As with other types of copolymers, random copolymers can have interesting and commercially desirable properties that blend those of the individual homopolymers. Examples of commercially relevant random copolymers include rubbers made from styrene-butadiene copolymers and resins from styrene-acrylic or methacrylic acid derivatives.  Copolymerization is particularly useful in tuning the glass transition temperature, which is important in the operating conditions of polymers; it is assumed that each monomer occupies the same amount of free volume whether it is in a copolymer or homopolymer, so the glass transition temperature falls between the Tg of each homopolymer and is dictated by the mole or mass fraction of each component.

text: Statistical copolymers are dictated by the reaction kinetics of the two chemically distinct monomer reactants, and are commonly referred to interchangeably as “random” in the polymer literature. As with other types of copolymers, random copolymers can have interesting and commercially desirable properties that blend those of the individual homopolymers. Examples of commercially relevant random copolymers include

text: rubber

text: s made from styrene-butadiene copolymers and resins from styrene-acrylic or

text: methacrylic acid

text: derivatives.  Copolymerization is particularly useful in tuning the

text: glass transition

text: temperature, which is important in the operating conditions of polymers; it is assumed that each monomer occupies the same amount of free volume whether it is in a copolymer or homopolymer, so the glass transition temperature falls between the Tg of each homopolymer and is dictated by the mole or mass fraction of each component.

text: Leptospermone can be synthesized from phloroglucinol by a reaction with isovaleroylnitrile in the presence of a zinc chloride catalyst.

text: Leptospermone

text: can be synthesized from phloroglucinol by a reaction with

text: isovaleroylnitrile

text: in the presence of a zinc chloride catalyst.

text: Polyaspartic chemistry was first introduced in the early 1990s making it a relatively new class of coating.  Polyaspartic is actually an aliphatic polyurea because it is derived from the reaction product of an aliphatic polyisocyanate component and a polyaspartic ester component, which is a new type of amine/diamine functional coreactant for aliphatic polyisocyanate.  Polyaspartic esters perform well as a reactive diluting agent for high solids polyurethane coatings.  For this reason, polyaspartic esters initially found use in conventional solvent-borne two-component polyurethane coatings.  Eventually, the advantages of using polyaspartic esters as the main component of the co-reactant for reaction with an aliphatic polyisocyanate in low to zero volatile organic compound (VOC) coatings has been realized. The rate of reaction of polyaspartic esters can be manipulated, thus extending the pot-life and controlling the cure rate of aliphatic coatings.  This allows formulators to create high solids coatings systems which are user-friendly with longer working times and still maintain a fast-cure.  Traditional aliphatic polyurea formulations required high-pressure, high-temperature plural component spray systems to be applied due to fast initial reaction rates.  Aliphatic polyaspartics can be formulated with slower reaction rates to accommodate batch-mixing and application by roller-applied methods or spray-applied through conventional single components paint sprayers without the use of solvent. As with aliphatic polyurethane or acrylic coatings, polyaspartic coatings are UV and light stable and will not yellow like aromatic epoxies, polyureas and polyurethanes.

text: Polyaspartic

text: chemistry

text: was first introduced in the early 1990s making it a relatively new class of

text: coating

text: .  Polyaspartic is actually an

text: aliphatic

text: polyurea

text: because it is derived from the

text: reaction

text: product of an aliphatic poly

text: isocyanate

text: component and a polyaspartic

text: ester

text: component, which is a new type of

text: amine

text: diamine

text: functional coreactant for aliphatic polyisocyanate.  Polyaspartic esters perform well as a reactive

text: diluting

text: agent for high solids

text: polyurethane

text: coatings.  For this reason, polyaspartic esters initially found use in conventional

text: solvent

text: -borne two-component polyurethane coatings.  Eventually, the advantages of using polyaspartic esters as the main component of the co-reactant for reaction with an aliphatic polyisocyanate in low to zero

text: volatile organic compound

text: (VOC) coatings has been realized. The rate of reaction of polyaspartic esters can be manipulated, thus extending the pot-life and controlling the cure rate of aliphatic coatings.  This allows formulators to create high solids coatings systems which are user-friendly with longer working times and still maintain a fast-cure.  Traditional aliphatic polyurea formulations required high-pressure, high-temperature plural component spray systems to be applied due to fast initial reaction rates.  Aliphatic polyaspartics can be formulated with slower reaction rates to accommodate batch-mixing and application by roller-applied methods or spray-applied through conventional single components paint sprayers without the use of solvent. As with aliphatic polyurethane or acrylic coatings, polyaspartic coatings are UV and light stable and will not yellow like aromatic epoxies, polyureas and polyurethanes.

text: Specialty chemicals are a category of relatively high valued, rapidly growing chemicals with diverse end product markets. Typical growth rates are one to three times GDP with prices over a dollar per pound. They are generally characterized by their innovative aspects. Products are sold for what they can do rather than for what chemicals they contain. Products include electronic chemicals, industrial gases, adhesives and sealants as well as coatings, industrial and institutional cleaning chemicals, and catalysts. In 2012, excluding fine chemicals, the $546 billion global speciality chemical market was 33% Paints, Coating and Surface Treatments, 27% Advanced Polymer, 14% Adhesives and Sealants, 13% additives and 13% pigments and inks.

text: Specialty chemicals

text: are a category of relatively high valued, rapidly growing chemicals with diverse end product markets. Typical growth rates are one to three times GDP with prices over a dollar per pound. They are generally characterized by their innovative aspects. Products are sold for what they can do rather than for what chemicals they contain. Products include electronic chemicals,

text: industrial gases

text: , adhesives and sealants as well as coatings, industrial and institutional cleaning chemicals, and catalysts. In 2012, excluding fine chemicals, the $546 billion global speciality chemical market was 33% Paints, Coating and Surface Treatments, 27% Advanced Polymer, 14% Adhesives and Sealants, 13% additives and 13% pigments and inks.

text: Pyridine (1) is reduced with sodium borohydride in presence of benzyl chloroformate to the Cbz protected dihydropyridine 2. The asymmetric Diels-Alder reaction with acrolein 3 is carried out with the McMillan catalyst to the aldehyde 4 as the endo isomer which is oxidized to the carboxylic acid 5 with sodium chlorite, monopotassium phosphate and 2-methyl-2-butene. Addition of bromine gives halolactonization product 6 and after replacement of the Cbz protective group by a BOC protective group in 7 (hydrogenolysis in the presence of di-tert-butyl dicarbonate) a carbonyl group is introduced in intermediate 8  by catalytic ruthenium(IV) oxide and sacrificial catalyst sodium periodate. Addition of ammonia cleaves the ester group to form amide 9 the alcohol group of which is mesylated to compound 10.  In the next step iodobenzene diacetate is added, converting the amide in a Hofmann rearrangement to the allyl carbamate 12 after capturing the intermediate isocyanate with allyl alcohol 11. On addition of sodium ethoxide in ethanol three reactions take place simultaneously: cleavage of the amide to form new an ethyl ester group, displacement of the mesyl group by newly formed BOC protected amine to an aziridine group and an elimination reaction forming the alkene group in 13 with liberation of HBr. In the final two steps the aziridine ring is opened by 3-pentanol 14 and boron trifluoride to aminoether 15 with the BOC group replaced by an acyl group and on removal of the other amine protecting group (Pd/C, PhP, and 1,3-dimethylbarbituric acid in ethanol) and addition of phosphoric acid oseltamivir 16 is obtained.

text: Pyridine (1) is

text: reduced

text: with

text: sodium borohydride

text: in presence of

text: benzyl chloroformate

text: to the

text: Cbz

text: protected

text: dihydropyridine

text: 2. The asymmetric Diels-Alder reaction with

text: acrolein

text: 3 is carried out with the

text: McMillan catalyst

text: to the

text: aldehyde

text: 4 as the

text: endo isomer

text: which is oxidized to the

text: carboxylic acid

text: 5 with

text: sodium chlorite

text: monopotassium phosphate

text: and

text: . Addition of

text: bromine

text: gives

text: halolactonization

text: product 6 and after replacement of the Cbz protective group by a

text: BOC

text: protective group in 7 (

text: hydrogenolysis

text: in the presence of

text: di-tert-butyl dicarbonate

text: ) a

text: carbonyl

text: group is introduced in intermediate 8  by catalytic

text: ruthenium(IV) oxide

text: and

text: sacrificial catalyst

text: sodium periodate

text: . Addition of

text: ammonia

text: cleaves the ester group to form

text: amide

text: 9 the

text: alcohol

text: group of which is

text: mesyl

text: ated to compound 10.  In the next step

text: iodobenzene diacetate

text: is added, converting the amide in a

text: Hofmann rearrangement

text: to the allyl

text: carbamate

text: 12 after capturing the intermediate isocyanate with

text: allyl alcohol

text: 11. On addition of

text: sodium ethoxide

text: in ethanol three reactions take place simultaneously: cleavage of the

text: amide

text: to form new an ethyl

text: ester

text: group, displacement of the mesyl group by newly formed BOC protected

text: amine

text: to an

text: aziridine

text: group and an

text: elimination reaction

text: forming the

text: alkene

text: group in 13 with liberation of HBr. In the final two steps the aziridine ring is opened by

text: 14 and

text: boron trifluoride

text: to aminoether 15 with the BOC group replaced by an

text: acyl

text: group and on removal of the other amine protecting group (

text: Pd/C

text: PhP

text: , and

text: 1,3-dimethylbarbituric acid

text: in ethanol) and addition of

text: phosphoric acid

text: oseltamivir 16 is obtained.

text: Last, but not least, the right choice of catalyst is important too. In acidic electrolytes the catalysts are usually precious metals like platinum, ruthenium, iridium and rhodium. In alkaline electrolytes, like zinc-air batteries and alkaline fuel cells, it is usual to use less expensive catalysts like carbon, manganese, silver, nickel foam or nickel mesh.

text: Last, but not least, the right choice of catalyst is important too. In acidic electrolytes the

text: catalyst

text: s are usually precious metals like

text: platinum

text: ruthenium

text: iridium

text: and

text: rhodium

text: . In alkaline electrolytes, like zinc-air batteries and

text: alkaline fuel cell

text: s, it is usual to use less expensive catalysts like

text: carbon

text: manganese

text: silver

text: nickel foam

text: or

text: nickel

text: mesh

text: Also required are the equations of state, relating the pressure, opacity and energy generation rate to other local variables appropriate for the material, such as temperature, density, chemical composition, etc.  Relevant equations of state for pressure may have to include the perfect gas law, radiation pressure, pressure due to degenerate electrons, etc. Opacity cannot be expressed exactly by a single formula. It is calculated for various compositions at specific densities and temperatures and presented in tabular form. Stellar structure codes (meaning computer programs calculating the model's variables) either interpolate in a density-temperature grid to obtain the opacity needed, or use a fitting function based on the tabulated values. A similar situation occurs for accurate calculations of the pressure equation of state. Finally, the nuclear energy generation rate is computed from nuclear physics experiments, using reaction networks to compute reaction rates for each individual reaction step and equilibrium abundances for each isotope in the gas.

text: Also required are the

text: equations of state

text: , relating the pressure, opacity and energy generation rate to other local variables appropriate for the material, such as temperature, density, chemical composition, etc.  Relevant equations of state for pressure may have to include the perfect gas law, radiation pressure, pressure due to degenerate electrons, etc. Opacity cannot be expressed exactly by a single formula. It is calculated for various compositions at specific densities and temperatures and presented in tabular form. Stellar structure codes (meaning computer programs calculating the model's variables) either interpolate in a density-temperature grid to obtain the opacity needed, or use a

text: fitting function

text: based on the tabulated values. A similar situation occurs for accurate calculations of the pressure equation of state. Finally, the nuclear energy generation rate is computed from

text: nuclear physics

text: experiments, using reaction networks to compute reaction rates for each individual reaction step and equilibrium abundances for each isotope in the gas.

text: Information about the mechanism of a reaction is often provided by the use of chemical kinetics to determine the rate equation and the reaction order in each reactant.

text: Information about the mechanism of a reaction is often provided by the use of

text: chemical kinetics

text: to determine the

text: rate equation

text: and the

text: reaction order

text: in each reactant.

text: As a system increases in size, system properties that depend on quantity of matter (with extensive properties) might change. The chemical and physical properties of a system affect each other and create varying results. The surface area to liquid ratio is a good example of such a property. On a small chemical scale, in a flask, say, there is a relatively large surface area to liquid ratio. However, if the reaction in question is scaled up to fit in a 500-gallon tank, the surface area to liquid ratio becomes much smaller. As a result of this difference in surface area to liquid ratio, the exact nature of the thermodynamics and the reaction kinetics of the process changes in a non-linear fashion. This is why a reaction in a beaker can behave vastly differently from the same reaction in a large-scale production process.

text: As a system increases in size, system properties that depend on quantity of matter (with

text: extensive properties

text: ) might change. The chemical and physical properties of a system affect each other and create varying results. The surface area to liquid ratio is a good example of such a property. On a small chemical scale, in a flask, say, there is a relatively large surface area to liquid ratio. However, if the reaction in question is scaled up to fit in a 500-gallon tank, the surface area to liquid ratio becomes much smaller. As a result of this difference in surface area to liquid ratio, the exact nature of the thermodynamics and the reaction kinetics of the process changes in a non-linear fashion. This is why a reaction in a beaker can behave vastly differently from the same reaction in a large-scale production process.

text: Alternately, the isokinetic (or isoequilibrium) temperature may be reached by observing that, if a linear relationship is found, then the difference between the ΔH's for any closely related reactants will be related to the difference between ΔS's for the same reactants:

text: The law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed. Hence, the quantity of mass is "conserved" over time. The law implies that mass can neither be created nor destroyed, although it may be rearranged in space, or the entities associated with it may be changed in form, as for example when light or physical work is transformed into particles that contribute the same mass to the system as the light or work had contributed. Thus, during any chemical reaction, nuclear reaction, or radioactive decay in an isolated system, the total mass of the reactants or starting materials must be equal to the mass of the products.

text: The law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of

text: matter

text: and

text: energy

text: , the

text: mass

text: of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed. Hence, the quantity of mass is "conserved" over time. The law implies that mass can neither be created nor destroyed, although it may be rearranged in space, or the entities associated with it may be changed in form, as for example when light or

text: physical work

text: is transformed into particles that contribute the same mass to the system as the light or work had contributed. Thus, during any

text: chemical reaction

text: nuclear reaction

text: , or

text: radioactive decay

text: in an isolated system, the total mass of the reactants or starting materials must be equal to the mass of the products.

text: In thermodynamics, chemical potential, also known as partial molar free energy, is a form of potential energy that can be absorbed or released during a chemical reaction or phase transition. The chemical potential of a species in a mixture is defined as the rate of change of a free energy of a thermodynamic system with respect to the change in the number of atoms or molecules of the species that are added to the system. Thus, it is the partial derivative of the free energy with respect to the amount of the species, all other species' concentrations in the mixture remaining constant. When both temperature and pressure are held constant, chemical potential is the partial molar Gibbs free energy. At chemical equilibrium or in phase equilibrium the total sum of chemical potentials is zero, as the free energy is at a minimum.

text: In

text: thermodynamics

text: , chemical potential, also known as partial molar free energy, is a form of

text: potential energy

text: that can be absorbed or released during a chemical reaction or

text: phase transition

text: . The chemical potential of a species in a mixture is defined as the rate of change of a

text: free energy

text: of a

text: thermodynamic system

text: with respect to the change in the number of atoms or molecules of the species that are added to the system. Thus, it is the

text: partial derivative

text: of the free energy with respect to the amount of the species, all other species' concentrations in the mixture remaining constant. When both temperature and pressure are held constant, chemical potential is the partial molar

text: Gibbs free energy

text: . At

text: chemical equilibrium

text: or in

text: phase equilibrium

text: the total sum of chemical potentials is zero, as the free energy is at a minimum.

text: For example the initial rate can be measured in a series of experiments at different initial concentrations of reactant A with all other concentrations [B], [C], ... kept constant, so that

text: Arenes are reactants in many organic reactions.

text: Chemical equations are used to graphically illustrate chemical reactions. They consist of chemical or structural formulas of the reactants on the left and those of the products on the right. They are separated by an arrow (→) which indicates the direction and type of the reaction; the arrow is read as the word "yields". The tip of the arrow points in the direction in which the reaction proceeds. A double arrow () pointing in opposite directions is used for equilibrium reactions. Equations should be balanced according to the stoichiometry, the number of atoms of each species should be the same on both sides of the equation. This is achieved by scaling the number of involved molecules (

text: Chemical equation

text: s are used to graphically illustrate chemical reactions. They consist of

text: chemical

text: or

text: structural formula

text: s of the reactants on the left and those of the products on the right. They are separated by an arrow (→) which indicates the direction and type of the reaction; the arrow is read as the word "yields". The tip of the arrow points in the direction in which the reaction proceeds. A double arrow () pointing in opposite directions is used for

text: equilibrium reaction

text: s. Equations should be balanced according to the

text: stoichiometry

text: , the number of atoms of each species should be the same on both sides of the equation. This is achieved by scaling the number of involved molecules (

text: Hexamethylbenzene can be prepared by the reaction of phenol with methanol at 400 °C in the presence of an alumina catalyst.

text: Hexamethylbenzene can be prepared by the reaction of

text: phenol

text: with

text: methanol

text: at 400 °C in the presence of an

text: alumina

text: catalyst

text: In a PFR, sometimes called continuous tubular reactor (CTR), one or more fluid reagents are pumped through a pipe or tube. The chemical reaction proceeds as the reagents travel through the PFR. In this type of reactor, the changing reaction rate creates a gradient with respect to distance traversed; at the inlet to the PFR the rate is very high, but as the concentrations of the reagents decrease and the concentration of the product(s) increases the reaction rate slows. Some important aspects of the PFR:

text: In a PFR, sometimes called continuous tubular reactor (CTR), one or more fluid reagents are

text: pump

text: ed through a pipe or tube. The chemical reaction proceeds as the reagents travel through the PFR. In this type of reactor, the changing reaction rate creates a

text: gradient

text: with respect to distance traversed; at the inlet to the PFR the rate is very high, but as the concentrations of the reagents decrease and the concentration of the product(s) increases the reaction rate slows. Some important aspects of the PFR:

text: Haensel worked on surface catalysts, patenting various methods for improving chemical processes in the oil industry.  Platinum was known to chemists as a catalyst, but was considered too expensive for industrial use.  Haensel, however, understood that only the surface mattered, so produced ceramic supports with tiny amounts of platinum metal on the surface, eventually showing that 0.01% could be effective.  It has since been realised that the platinum was in the form of nanoparticles, long before this idea was common.  The metal combined with the acid surface of alumina to carry out two chemical processes, resulting in the production of  gasoline with a higher octane rating.  At that time, octane rating was improved by the addition of anti-knock agents such as tetraethyllead.  The development of the platforming process allowed the eventual removal of lead from gasoline. In addition, hydrogen was produced, which was valuable in itself but also helped to remove sulfur, giving a cleaner, more environmentally friendly process.

text: Haensel worked on surface

text: catalyst

text: s, patenting various methods for improving chemical processes in the oil industry.

text: Platinum

text: was known to chemists as a catalyst, but was considered too expensive for industrial use.  Haensel, however, understood that only the surface mattered, so produced ceramic supports with tiny amounts of platinum metal on the surface, eventually showing that 0.01% could be effective.  It has since been realised that the platinum was in the form of

text: nanoparticle

text: s, long before this idea was common.  The metal combined with the acid surface of

text: alumina

text: to carry out two chemical processes, resulting in the production of

text: gasoline

text: with a higher

text: octane rating

text: .  At that time, octane rating was improved by the addition of

text: anti-knock agent

text: s such as

text: tetraethyllead

text: .  The development of the platforming process allowed the eventual removal of lead from gasoline. In addition,

text: hydrogen

text: was produced, which was valuable in itself but also helped to remove

text: sulfur

text: , giving a cleaner, more

text: environmentally friendly

text: process.

text: The temperature achieved during the reaction determines the outcome. In an ideal case, the reaction produces a well-separated melt of metal and slag. For this, the temperature has to be high enough to melt both the reaction products, the resulting metal and the fuel oxide. Too low temperature will result in a mixture of sintered metal and slag, too high temperature – above boiling point of any reactant or product – will lead to rapid production of gas, dispersing the burning reaction mixture, sometimes with effects similar to a low-yield explosion.  In compositions intended for production of metal by aluminothermic reaction, these effects can be counteracted. Too low reaction temperature (e.g. when producing silicon from sand) can be boosted with addition of a suitable oxidizer (e.g. sulfur in aluminium-sulfur-sand compositions), too high temperatures can be reduced by using a suitable coolant and/or slag flux. The flux often used in amateur compositions is calcium fluoride, as it reacts only minimally, has relatively low melting point, low melt viscosity at high temperatures (therefore increasing fluidity of the slag) and forms a eutectic with alumina. Too much of flux however dilutes the reactants to the point of not being able to sustain combustion. The type of metal oxide also has dramatic influence to the amount of energy produced; the higher the oxide, the higher the amount of energy produced. A good example is the difference between manganese(IV) oxide and manganese(II) oxide, where the former produces too high temperature and the latter is barely able to sustain combustion; to achieve good results a mixture with proper ratio of both oxides should be used.

text: The temperature achieved during the reaction determines the outcome. In an ideal case, the reaction produces a well-separated melt of metal and slag. For this, the temperature has to be high enough to melt both the reaction products, the resulting metal and the fuel oxide. Too low temperature will result in a mixture of sintered metal and slag, too high temperature – above boiling point of any reactant or product – will lead to rapid production of gas, dispersing the burning reaction mixture, sometimes with effects similar to a low-yield explosion.  In compositions intended for production of metal by

text: aluminothermic reaction

text: , these effects can be counteracted. Too low reaction temperature (e.g. when producing silicon from sand) can be boosted with addition of a suitable oxidizer (e.g. sulfur in aluminium-sulfur-sand compositions), too high temperatures can be reduced by using a suitable coolant and/or slag

text: flux

text: . The flux often used in amateur compositions is

text: calcium fluoride

text: , as it reacts only minimally, has relatively low melting point, low melt viscosity at high temperatures (therefore increasing fluidity of the slag) and forms a eutectic with alumina. Too much of flux however dilutes the reactants to the point of not being able to sustain combustion. The type of metal oxide also has dramatic influence to the amount of energy produced; the higher the oxide, the higher the amount of energy produced. A good example is the difference between

text: manganese(IV) oxide

text: and

text: manganese(II) oxide

text: , where the former produces too high temperature and the latter is barely able to sustain combustion; to achieve good results a mixture with proper ratio of both oxides should be used.

text: An isodesmic reaction is a chemical reaction in which the type of chemical bonds broken in the reactant are the same as the type of bonds formed in the reaction product. This type of reaction is often used as a hypothetical reaction in thermochemistry.

text: An isodesmic reaction is a

text: chemical reaction

text: in which the type of

text: chemical bond

text: s broken in the

text: reactant

text: are the same as the type of bonds formed in the reaction product. This type of reaction is often used as a hypothetical reaction in

text: thermochemistry

text: The maximum and minimum for any ξ occur whenever the first of the reactants is depleted for the forward reaction; or the first of the "products" is depleted if the reaction as viewed as being pushed in the reverse direction. This is a purely kinematic restriction on the reaction simplex, a hyperplane in composition space, or N‑space, whose dimensionality equals the number of linearly-independent chemical reactions. This is necessarily less than the number of chemical components, since each reaction manifests a relation between at least two chemicals. The accessible region of the hyperplane depends on the amounts of each chemical species actually present, a contingent fact. Different such amounts can even generate different hyperplanes, all sharing the same algebraic stoichiometry.

text: The

text: maximum and minimum

text: for any ξ occur whenever the first of the reactants is depleted for the forward reaction; or the first of the "products" is depleted if the reaction as viewed as being pushed in the reverse direction. This is a purely

text: kinematic

text: restriction on the reaction

text: simplex

text: , a

text: hyperplane

text: in composition space, or N‑space, whose

text: dimension

text: ality equals the number of

text: linearly-independent

text: chemical reactions. This is necessarily less than the number of chemical components, since each reaction manifests a relation between at least two chemicals. The accessible region of the hyperplane depends on the amounts of each chemical species actually present, a contingent fact. Different such amounts can even generate different hyperplanes, all sharing the same algebraic stoichiometry.

text: Enzyme catalysis is the increase in the rate of a chemical reaction by the active site of a protein. The protein catalyst (enzyme) may be part of a multi-subunit complex, and/or may transiently or permanently associate with a Cofactor (e.g. adenosine triphosphate). Catalysis of biochemical reactions in the cell is vital due to the very low reaction rates of the uncatalysed reactions at room temperature and pressure. A key driver of protein evolution is the optimization of such catalytic activities via protein dynamics.

text: Enzyme catalysis is the increase in the

text: rate

text: of a

text: chemical reaction

text: by the

text: active site

text: of a

text: protein

text: . The protein

text: catalyst

text: enzyme

text: ) may be part of a

text: multi-subunit complex

text: , and/or may transiently or permanently associate with a

text: Cofactor

text: (e.g.

text: adenosine triphosphate

text: Catalysis

text: of

text: biochemical

text: reactions in the

text: cell

text: is vital due to the very low reaction rates of the uncatalysed reactions at room temperature and pressure. A key driver of protein evolution is the optimization of such catalytic activities via

text: protein dynamics

text: A positive non-linear effect, (+)-NLE, is present in an asymmetric reaction which demonstrates a higher product ee (ee ) than predicted by an ideal linear situation (Figure 1).  It is often referred to as asymmetric amplification, a term coined by Oguni and co-workers. An example of a positive non-linear effect is observed in the case of Sharpless epoxidation with the substrate geraniol. In all cases of chemical reactivity exhibiting (+)-NLE, there is an innate tradeoff between overall reaction rate and enantioselectivity. The overall rate is slower and the enantioselectivity is higher relative to a linear behaving reaction.

text: A positive non-linear effect, (+)-NLE, is present in an asymmetric reaction which demonstrates a higher product ee (ee ) than predicted by an ideal linear situation (Figure 1).  It is often referred to as asymmetric amplification, a term coined by Oguni and co-workers. An example of a positive non-linear effect is observed in the case of Sharpless

text: epoxidation

text: with the substrate geraniol. In all cases of chemical reactivity exhibiting (+)-NLE, there is an innate tradeoff between overall reaction rate and enantioselectivity. The overall rate is slower and the enantioselectivity is higher relative to a linear behaving reaction.

text: Strictly speaking the above equation holds also for systems with chemical reactions if the terms in the balance equation are taken to refer to total mass, i.e. the sum of all the chemical species of the system. In the absence of a chemical reaction the amount of any chemical species flowing in and out will be the same; this gives rise to an equation for each species present in the system. However, if this is not the case then the mass balance equation must be amended to allow for the generation or depletion (consumption) of each chemical species. Some use one term in this equation to account for chemical reactions, which will be negative for depletion and positive for generation. However, the conventional form of this equation is written to account for both a positive generation term (i.e. product of reaction) and a negative consumption term (the reactants used to produce the products). Although overall one term will account for the total balance on the system, if this balance equation is to be applied to an individual species and then the entire process, both terms are necessary. This modified equation can be used not only for reactive systems, but for population balances such as arise in particle mechanics problems. The equation is given below; note that it simplifies to the earlier equation in the case that the generation term is zero.

text: Strictly speaking the above equation holds also for systems with

text: chemical reaction

text: particle mechanics

text: problems. The equation is given below; note that it simplifies to the earlier equation in the case that the generation term is zero.

text: Phenyl-2-nitropropene is a chemical compound with the chemical formula is CHNO. It can be produced by the reaction of benzaldehyde and nitroethane in the presence of a basic catalyst. In this reaction, the base deprotonates nitroethane to form a resonance stabilized anion. This anion nucleophilically adds to the aldehyde forming a beta nitro alcohol, which is subsequently dehydrated to yield the nitroalkene. This reaction is known as a nitroaldol reaction. Phenyl-2-nitropropene can be reduced in the presence of a catalyst to produce phenylacetone, which is a controlled precursor of methamphetamine. However, with lithium aluminium hydride it can simply be reduced to directly form amphetamine in moderate yields.

text: Phenyl-2-nitropropene is a

text: chemical compound

text: with the chemical formula is CHNO. It can be produced by the reaction of

text: benzaldehyde

text: and

text: nitroethane

text: in the presence of a basic catalyst. In this reaction, the base deprotonates nitroethane to form a resonance stabilized anion. This anion nucleophilically adds to the aldehyde forming a beta nitro alcohol, which is subsequently dehydrated to yield the

text: nitroalkene

text: . This reaction is known as a

text: nitroaldol reaction

text: . Phenyl-2-nitropropene can be

text: reduced

text: in the presence of a catalyst to produce

text: phenylacetone

text: , which is a controlled precursor of methamphetamine. However, with

text: lithium aluminium hydride

text: it can simply be reduced to directly form

text: amphetamine

text: in moderate yields.

text: If the temperature was increased, the heat content of the system would increase, so the system would consume some of that heat by shifting the equilibrium to the left, thereby producing less ammonia. More ammonia would be produced if the reaction was run at a lower temperature, but a lower temperature also lowers the rate of the process, so, in practice (the Haber process) the temperature is set at a compromise value that allows ammonia to be made at a reasonable rate with an equilibrium concentration that is not too unfavorable.

text: If the temperature was increased, the heat content of the system would increase, so the system would consume some of that heat by shifting the equilibrium to the left, thereby producing less ammonia. More ammonia would be produced if the reaction was run at a lower temperature, but a lower temperature also lowers the rate of the process, so, in practice (the

text: Haber process

text: ) the temperature is set at a compromise value that allows

text: ammonia

text: to be made at a reasonable rate with an equilibrium concentration that is not too unfavorable.

text: There are certain conditions that must be met for this chain reaction to occur. Certain fuel densities are necessary, or the neutrons won't impact a sufficient number of other unstable atoms before escaping the reactor. It is also easier for unstable nuclei to absorb neutrons when the neutrons are traveling at a certain speed. For , slower neutrons are more likely to cause a fission reaction. In order to slow down the neutrons in a reactor core, a moderator is used. Water is the most common moderator in use today. The neutrons are slowed down as they travel through the water. As the reaction speeds up and the temperature of the reactor increases, increasing the temperature of the moderator, the neutrons aren’t slowed down as effectively. This in turn reduces the rate of nuclear reactions inside the core, since the faster neutrons aren’t as easy to absorb. This effect, the negative temperature coefficient, makes the reactor inherently resistant to "excursion", or a sudden, uncontrolled increase in temperature.

text: There are certain conditions that must be met for this chain reaction to occur. Certain fuel densities are necessary, or the neutrons won't impact a sufficient number of other unstable atoms before escaping the reactor. It is also easier for unstable nuclei to absorb neutrons when the neutrons are traveling at a certain speed. For , slower neutrons are more likely to cause a fission reaction. In order to slow down the neutrons in a reactor core, a

text: moderator

text: is used. Water is the most common moderator in use today. The neutrons are slowed down as they travel through the water. As the reaction speeds up and the temperature of the reactor increases, increasing the temperature of the moderator, the neutrons aren’t slowed down as effectively. This in turn reduces the rate of nuclear reactions inside the core, since the faster neutrons aren’t as easy to absorb. This effect, the negative

text: temperature coefficient

text: , makes the reactor inherently resistant to "

text: excursion

text: ", or a sudden, uncontrolled increase in temperature.

text: The concept of chemical equilibrium was developed after Berthollet (1803) found that some chemical reactions are reversible. For any reaction mixture to exist at equilibrium, the rates of the forward and backward (reverse) reactions are equal. In the following chemical equation with arrows pointing both ways to indicate equilibrium, A and B are reactant chemical species, S and T are product species, and α, β, σ, and τ are the stoichiometric coefficients of the respective reactants and products:

text: The concept of chemical equilibrium was developed after

text: Berthollet

text: (1803) found that some

text: chemical reaction

text: s are

text: reversible

text: . For any reaction mixture to exist at equilibrium, the

text: rates

text: of the forward and backward (reverse) reactions are equal. In the following

text: chemical equation

text: with arrows pointing both ways to indicate equilibrium, A and B are

text: reactant

text: chemical species, S and T are product species, and

text: α

text: β

text: σ

text: , and

text: τ

text: are the

text: stoichiometric coefficient

text: s of the respective reactants and products:

text: The mole is widely used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions.  For example, the chemical equation  implies that 2 mol of dihydrogen (H) and 1 mol of dioxygen (O) react to form 2 mol of water (HO). The mole may also be used to express the number of atoms, ions, or other elementary entities in a given sample of any substance. The concentration of a solution is commonly expressed by its molarity, defined as the number of moles of the dissolved substance per litre of solution.

text: The mole is widely used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions.  For example, the chemical equation  implies that 2 mol of

text: dihydrogen

text: (H) and 1 mol of

text: dioxygen

text: (O) react to form 2 mol of water (HO). The mole may also be used to express the number of atoms, ions, or other elementary entities in a given sample of any substance. The

text: concentration

text: of a solution is commonly expressed by its

text: molarity

text: , defined as the number of moles of the dissolved substance per

text: litre

text: of solution.

text: is among the fastest chemical reactions known, with a reaction rate constant of  at room temperature. Such a rapid rate is characteristic of a diffusion-controlled reaction, in which the rate is limited by the speed of molecular diffusion.

text: is among the fastest chemical reactions known, with a

text: reaction rate constant

text: of  at room temperature. Such a rapid rate is characteristic of a

text: diffusion-controlled reaction

text: , in which the rate is limited by the speed of molecular

text: diffusion

text: In MOCVD, group III alkyls are already partially dissociated in the gas stream. These diffuse through a stagnant boundary layer that exists over the heated substrate, after which they dissociate into the atomic group III elements. These atoms then migrate to the appropriate lattice site and deposit epitaxially by associating with a group V atom that was derived from the thermal decomposition of the hydrides. The growth rate here is usually limited by the diffusion rate of the group III alkyls through the boundary layer. Gas phase reactions between the reactants have also been observed in this process.

text: R is the net rate of production of species i by chemical reaction and S is the rate of creation by addition from the dispersed phase and the user defined source. J is the diffusion flux of species i, which arises due to concentration gradients and differs in both laminar and turbulent flows. In turbulent flows, computational fluid dynamics also considers the effects of turbulent diffusivity. The net source of chemical species i due to reaction, R which appeared as the source term in the species transport equation is computed as the sum of the reaction sources over the N reactions that the species participate in.

text: R is the net rate of production of species i by chemical reaction and S is the rate of creation by addition from the dispersed phase and the user defined source. J is the diffusion flux of species i, which arises due to concentration gradients and differs in both laminar and turbulent flows. In turbulent flows,

text: computational fluid dynamics

text: also considers the effects of

text: turbulent

text: diffusivity. The net source of chemical species i due to reaction, R which appeared as the source term in the species transport equation is computed as the sum of the reaction sources over the N reactions that the species participate in.

text: Of course, the reactants should also be mixed in the optimal proportions. This is the case when each reactant ion plus its associated electrons accounts for half the pressure. Assuming that the total pressure is fixed, this means that density of the non-hydrogenic ion is smaller than that of the hydrogenic ion by a factor 2/(Z+1). Therefore, the rate for these reactions is reduced by the same factor, on top of any differences in the values of <σv>/T. On the other hand, because the - reaction has only one reactant, its rate is twice as high as when the fuel is divided between two different hydrogenic species, thus creating a more efficient reaction.

text: Bimolecular reactions are highly dependent on the concentration of substrates. Therefore, when a supramolecular container encapsulates both reactants within its small cavity, the effective local concentration of the reactants is increased and, as a result of an entropic effect, the rate of the reaction is accelerated. That is to say an intramolecular reaction is faster than its corresponding intermolecular reaction.

text: Bimolecular

text: reactions are highly dependent on the concentration of substrates. Therefore, when a supramolecular container encapsulates both reactants within its small cavity, the

text: effective local concentration

text: of the reactants is increased and, as a result of an entropic effect, the rate of the reaction is accelerated. That is to say an intramolecular reaction is faster than its corresponding intermolecular reaction.

text: The partial order with respect to a given reactant can be evaluated by the method of flooding (or of isolation) of Ostwald. In this method, the concentration of one reactant is measured with all other reactants in large excess so that their concentration remains essentially constant. For a reaction a·A + b·B → c·C with rate law:

text: The partial order with respect to a given reactant can be evaluated by the method of flooding (or of isolation) of

text: Ostwald

text: . In this method, the concentration of one reactant is measured with all other reactants in large excess so that their concentration remains essentially constant. For a reaction a·A + b·B → c·C with rate law:

text: In enzymology, a riboflavinase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , a riboflavinase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: Many traditional chemical conversions used in various industries suffer from inherent drawbacks from both an economic and environmental viewpoint. Non-specific reactions can afford low product yields, copious amounts of waste and impure products. The need for elevated temperatures and pressures leads to high energy consumption and high capital investment costs. Disposal of unwanted by-products may be difficult and/or expensive and hazardous solvents may be required. In stark contrast, enzymatic reactions are performed under mild conditions of temperature and pressure, in water as solvent, and exhibit very high rates and are often highly specific. Moreover, they are produced from renewable raw materials and are biodegradable. In addition, the mild operating conditions of enzymatic processes mean that they can be performed in relatively simple equipment and are easy to control. In short, they reduce the environmental footprint of manufacturing by reducing the consumption of energy and chemicals and concomitant generation of waste.

text: Many traditional chemical conversions used in various industries suffer from inherent drawbacks from both an economic and environmental viewpoint. Non-specific reactions can afford low product yields, copious amounts of waste and impure products. The need for elevated temperatures and pressures leads to high energy consumption and high

text: capital investment

text: costs. Disposal of unwanted by-products may be difficult and/or expensive and hazardous solvents may be required. In stark contrast, enzymatic reactions are performed under mild conditions of temperature and pressure, in water as solvent, and exhibit very high rates and are often highly specific. Moreover, they are produced from renewable raw materials and are

text: biodegradable

text: . In addition, the mild operating conditions of enzymatic processes mean that they can be performed in relatively simple equipment and are easy to control. In short, they reduce the environmental footprint of manufacturing by reducing the consumption of energy and chemicals and concomitant generation of waste.

text: The diagram shows a typical reflux apparatus for applying energy to chemical reactions. It includes an optional beaker of water between the reactants and the heat. This is often used as a safety precaution when using flammable reactants and a Bunsen burner in order to keep the flame away from the reactants. In modern laboratories, open flames are avoided due to the many flammable solvents often in use, and electrical heating, (e.g., with a hot plate or mantle) is preferred. Furthermore, a high boiling, thermally stable silicone oil is generally used to immerse the reaction vessel, rather than water which evaporates too readily to be useful for lengthy reactions. Using an oil bath, temperatures of up to several hundred degrees can easily be achieved, which is higher than the boiling point of most commonly used solvents. If even higher temperatures are required, the oil bath can be replaced with a sand bath.

text: The diagram shows a typical reflux apparatus for applying energy to chemical reactions. It includes an optional beaker of water between the reactants and the heat. This is often used as a safety precaution when using flammable reactants and a

text: Bunsen burner

text: in order to keep the flame away from the reactants. In modern laboratories, open flames are avoided due to the many flammable solvents often in use, and electrical heating, (e.g., with a

text: hot plate

text: or mantle) is preferred. Furthermore, a high boiling, thermally stable

text: silicone oil

text: is generally used to immerse the reaction vessel, rather than water which evaporates too readily to be useful for lengthy reactions. Using an oil bath, temperatures of up to several hundred degrees can easily be achieved, which is higher than the boiling point of most commonly used

text: solvent

text: s. If even higher temperatures are required, the oil bath can be replaced with a

text: sand bath

text: In enzymology, a guanidinoacetase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , a guanidinoacetase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: Catalytic activity is usually denoted by the symbol z  and measured in mol/s, a unit which was called katal and defined the SI unit for catalytic activity since 1999. Catalytic activity is not a kind of reaction rate, but a property of the catalyst under certain conditions, in relation to a specific chemical reaction. Catalytic activity of one katal (Symbol 1 kat = 1 mol/s) of a catalyst means an amount of that catalyst (substance, in Mol) that leads to a net reaction of one Mol per second of the reactants to the resulting reagents or other outcome which was intended for this chemical reaction. A catalyst may and usually will have different catalytic activity for distinct reactions. See katal for an example.

text: Catalytic activity is usually denoted by the symbol z  and measured in

text: mol

text: /s, a unit which was called

text: katal

text: and defined the SI unit for catalytic activity since 1999. Catalytic activity is not a kind of reaction rate, but a property of the

text: catalyst

text: under certain conditions, in relation to a specific

text: chemical reaction

text: . Catalytic activity of one katal (Symbol 1 kat = 1 mol/s) of a catalyst means an amount of that catalyst (substance, in

text: Mol

text: ) that leads to a net reaction of one Mol per second of the reactants to the resulting

text: reagent

text: s or other outcome which was intended for this chemical reaction. A catalyst may and usually will have different catalytic activity for distinct reactions. See

text: katal

text: for an example.

text: This deoxygenation reaction is a radical substitution. In the related Barton decarboxylation the reactant is a carboxylic acid.

text: This deoxygenation reaction is a

text: radical substitution

text: . In the related

text: Barton decarboxylation

text: the reactant is a

text: carboxylic acid

text: In the case of saturation kinetics described above, provided that [A] is not present in a large excess relative to [B], saturation conditions will only apply at the beginning of the reaction. As the substrate is consumed, the concentration decreases and eventually [A] is no longer sufficient to completely overwhelm [Cat]. This is manifested by a gradual change in rate from 0-order to some higher (i.e. 1st, 2nd, etc.) order in [A]. This can also be described as a change in catalyst resting state from the bound form to the unbound form over the course of the reaction.

text: The rate of a chemical reaction is influenced by many different factors, such as temperature, pH, reactant and product concentrations and other effectors. The degree to which these factors change the reaction rate is described by the elasticity coefficient. This coefficient is defined as follows:

text: The rate of a chemical reaction is influenced by many different factors, such as temperature,

text: pH

text: reactant

text: and

text: product

text: concentrations and other effectors. The degree to which these factors change the reaction rate is described by the elasticity coefficient. This coefficient is defined as follows:

text: Such reactions are conducted in the presence of acidic catalysts. The other principal route to thiols involves the addition of hydrogen sulfide to alkenes. Such reactions are usually conducted in the presence of an acid catalyst or UV light. Halide displacement, using the suitable organic halide and sodium hydrogen sulfide has also been utilized.

text: Such reactions are conducted in the presence of acidic catalysts. The other principal route to thiols involves the addition of hydrogen sulfide to alkenes. Such reactions are usually conducted in the presence of an acid

text: catalyst

text: or UV light. Halide displacement, using the suitable organic halide and sodium hydrogen sulfide has also been utilized.

text: In enzymology, an anhydrosialidase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , an anhydrosialidase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: The development of diphenylphosphinobinapthyl (BINAP) and diphenylphosphinoferrocene (DPPF) as ligands for the Buchwald–Hartwig amination provided the first reliable extension to primary amines and allowed efficient coupling of aryl iodides and triflates. (It is believed that the bidentate ligands prevent formation of the palladium iodide dimer after oxidative addition, speeding up the reaction.) These ligands typically produce the coupled products at higher rates and better yields than the first generation of catalysts. The initial reports of these ligands as catalysts were somewhat unexpected given the mechanistic evidence for monoligated complexes serving as the active catalysts in the first-generation system. In fact, the first examples from both labs were published in the same issue of JACS.

text: The development of

text: diphenylphosphinobinapthyl

text: (BINAP) and

text: diphenylphosphinoferrocene

text: (DPPF) as ligands for the Buchwald–Hartwig amination provided the first reliable extension to primary amines and allowed efficient coupling of aryl iodides and triflates. (It is believed that the bidentate ligands prevent formation of the palladium iodide dimer after oxidative addition, speeding up the reaction.) These ligands typically produce the coupled products at higher rates and better yields than the first generation of catalysts. The initial reports of these ligands as catalysts were somewhat unexpected given the mechanistic evidence for monoligated complexes serving as the active catalysts in the first-generation system. In fact, the first examples from both labs were published in the same issue of

entity_name: Journal of the American Chemical Society

text: JACS

text: Propane dehydrogenation (PDH) converts propane into propene and by-product hydrogen. The propene from propane yield is about 85 m%. Reaction by-products (mainly hydrogen) are usually used as fuel for the propane dehydrogenation reaction. As a result, propene tends to be the only product, unless local demand exists for hydrogen.  This route is popular in regions, such as the Middle East, where there is an abundance of propane from oil/gas operations. In this region, the propane output is expected to be capable of supplying not only domestic needs, but also the demand from China, where many PDH projects are scheduled to go on stream.  However, as natural gas offerings in the United States are significantly increasing due to the rising exploitation of shale gas, propane prices are decreasing.  Chemical companies are already planning to establish PDH plants in the USA to take advantage of the low price raw material, obtained from shale gas. Numerous plants dedicated to propane dehydrogenation are currently under construction around the world.  There are already five licensed technologies. The propane dehydrogenation process may be accomplished through different commercial technologies. The main differences between each of them concerns the catalyst employed, design of the reactor and strategies to achieve higher conversion rates.

text: Propane

text: dehydrogenation

text: (PDH) converts propane into propene and by-product hydrogen. The propene from propane yield is about 85 m%. Reaction by-products (mainly hydrogen) are usually used as fuel for the propane dehydrogenation reaction. As a result, propene tends to be the only product, unless local demand exists for hydrogen.  This route is popular in regions, such as the

text: Middle East

text: , where there is an abundance of

text: propane

text: from oil/gas operations. In this region, the propane output is expected to be capable of supplying not only domestic needs, but also the demand from China, where many PDH projects are scheduled to go on stream.  However, as natural gas offerings in the United States are significantly increasing due to the rising exploitation of shale gas,

text: propane

text: prices are decreasing.  Chemical companies are already planning to establish PDH plants in the USA to take advantage of the low price raw material, obtained from shale gas. Numerous plants dedicated to

text: propane

text: dehydrogenation are currently under construction around the world.  There are already five licensed technologies. The propane dehydrogenation process may be accomplished through different commercial technologies. The main differences between each of them concerns the catalyst employed, design of the reactor and strategies to achieve higher conversion rates.

text: Substrate analogs (substrate state analogues), are chemical compounds with a chemical structure that resemble the substrate molecule in an enzyme-catalyzed chemical reaction. Substrate analogs can act as competitive inhibitors of an enzymatic reaction. An example is phosphoramidate to the Tetrahymena group I ribozyme

text: Substrate analogs (substrate state analogues), are

text: chemical compound

text: s with a

text: chemical structure

text: that resemble the

text: substrate molecule

text: in an

text: enzyme-catalyzed

text: chemical reaction

text: . Substrate analogs can act as competitive inhibitors of an enzymatic reaction. An example is phosphoramidate to the Tetrahymena group I ribozyme

text: Kirchhoff showed in 1858 that the variation of the heat of a chemical reaction is given by the difference in heat capacity between products and reactants: dΔH / dT = ΔC. Integration of this equation permits the evaluation of the heat of reaction at one temperature from measurements at another temperature.

text: Kirchhoff showed in 1858 that the variation of the heat of a chemical reaction is given by the difference in

text: heat capacity

text: A reaction can also have an undefined reaction order with respect to a reactant if the rate is not simply proportional to some power of the concentration of that reactant; for example, one cannot talk about reaction order in the rate equation for a bimolecular reaction between adsorbed molecules:

text: A reaction can also have an undefined reaction order with respect to a reactant if the rate is not simply proportional to some power of the concentration of that reactant; for example, one cannot talk about reaction order in the rate equation for a bimolecular reaction between

text: adsorbed molecules

text: The reaction rate (rate of reaction)  or speed of reaction for a reactant or product in a particular reaction is intuitively defined as how quickly or slowly a reaction takes place. For example, the oxidative rusting of iron under Earth's atmosphere is a slow reaction that can take many years, but the combustion of cellulose in a fire is a reaction that takes place in fractions of a second.

text: The reaction rate (rate of reaction)  or speed of reaction for a

text: reactant

text: or

text: product

text: in a particular

text: reaction

text: is intuitively defined as how quickly or slowly a reaction takes place. For example, the

text: oxidative rusting

text: of

text: iron

text: under

text: Earth's atmosphere

text: is a slow reaction that can take many years, but the combustion of

text: cellulose

text: in a fire is a reaction that takes place in fractions of a second.

text: For zero-order reactions, the reaction rate is independent of the concentration of a reactant, so that changing its concentration has no effect on the speed of the reaction. This may occur when there is a bottleneck which limits the number of reactant molecules that can react at the same time, for example if the reaction requires contact with an enzyme or a catalytic surface.

text: For zero-order reactions, the

text: reaction rate

text: is independent of the concentration of a reactant, so that changing its concentration has no effect on the speed of the reaction. This may occur when there is a bottleneck which limits the number of reactant molecules that can react at the same time, for example if the reaction requires contact with an enzyme or a catalytic surface.

text: In a solid, only those particles that are at the surface can be involved in a reaction. Crushing a solid into smaller parts means that more particles are present at the surface, and the frequency of collisions between these and reactant particles increases, and so reaction occurs more rapidly. For example, Sherbet (powder) is a mixture of very fine powder of malic acid (a weak organic acid) and sodium hydrogen carbonate. On contact with the saliva in the mouth, these chemicals quickly dissolve and react, releasing carbon dioxide and providing for the fizzy sensation. Also, fireworks manufacturers modify the surface area of solid reactants to control the rate at which the fuels in fireworks are oxidised, using this to create different effects. For example, finely divided aluminium confined in a shell explodes violently. If larger pieces of aluminium are used, the reaction is slower and sparks are seen as pieces of burning metal are ejected.

text: In a solid, only those particles that are at the surface can be involved in a reaction. Crushing a solid into smaller parts means that more particles are present at the surface, and the frequency of collisions between these and reactant particles increases, and so reaction occurs more rapidly. For example,

text: Sherbet (powder)

text: is a mixture of very fine powder of

text: malic acid

text: (a weak organic acid) and

text: sodium hydrogen carbonate

text: . On contact with the

text: saliva

text: in the mouth, these chemicals quickly dissolve and react, releasing

text: carbon dioxide

text: and providing for the fizzy sensation. Also,

text: fireworks

text: manufacturers modify the surface area of solid reactants to control the rate at which the fuels in fireworks are oxidised, using this to create different effects. For example, finely divided

text: aluminium

text: confined in a shell explodes violently. If larger pieces of aluminium are used, the reaction is slower and sparks are seen as pieces of burning metal are ejected.

text: In enzymology, a diguanidinobutanase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , a diguanidinobutanase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: The idea behind parity symmetry is that the equations of particle physics are invariant under mirror inversion. This leads to the prediction that the mirror image of a reaction (such as a chemical reaction or radioactive decay) occurs at the same rate as the original reaction. Parity symmetry appears to be valid for all reactions involving electromagnetism and strong interactions. Until 1956, parity conservation was believed to be one of the fundamental geometric conservation laws (along with conservation of energy and conservation of momentum). However, in 1956 a careful critical review of the existing experimental data by theoretical physicists Tsung-Dao Lee and Chen-Ning Yang revealed that while parity conservation had been verified in decays by the strong or electromagnetic interactions, it was untested in the weak interaction. They proposed several possible direct experimental tests. The first test based on beta decay of cobalt-60 nuclei was carried out in 1956 by a group led by Chien-Shiung Wu, and demonstrated conclusively that weak interactions violate the P symmetry or, as the analogy goes, some reactions did not occur as often as their mirror image.

text: The idea behind parity symmetry is that the equations of particle physics are invariant under mirror inversion. This leads to the prediction that the mirror image of a reaction (such as a

text: chemical reaction

text: or

text: radioactive decay

text: ) occurs at the same rate as the original reaction. Parity symmetry appears to be valid for all reactions involving

text: electromagnetism

text: and

text: strong interaction

text: s. Until 1956, parity conservation was believed to be one of the fundamental geometric conservation laws (along with

text: conservation of energy

text: and

text: conservation of momentum

text: ). However, in 1956 a careful critical review of the existing experimental data by theoretical physicists

text: Tsung-Dao Lee

text: and

text: Chen-Ning Yang

text: revealed that while parity conservation had been verified in decays by the strong or electromagnetic interactions, it was untested in the weak interaction. They proposed several possible direct experimental tests. The first test based on

text: beta decay

text: of

text: nuclei was carried out in 1956 by a group led by

text: Chien-Shiung Wu

text: , and demonstrated conclusively that weak interactions violate the P symmetry or, as the analogy goes, some reactions did not occur as often as their mirror image.

text: Christiansen and Kramers also noted that if, in one link of the reaction chain, two or more unstable molecules are produced, the reaction chain would branch and grow. The result is in fact an exponential growth, thus giving rise to explosive increases in reaction rates, and indeed to chemical explosions themselves. This was the first proposal for the mechanism of chemical explosions.

text: Christiansen and Kramers also noted that if, in one link of the reaction chain, two or more unstable

text: molecules

text: are produced, the reaction chain would branch and grow. The result is in fact an exponential growth, thus giving rise to explosive increases in reaction rates, and indeed to chemical explosions themselves. This was the first proposal for the mechanism of chemical explosions.

text: The composition of solutions containing reactants A and H is easy to calculate as a function of p[H]. When [H] is known, the free concentration [A] is calculated from the mass-balance equation in A.

text: The composition of solutions containing reactants A and H is easy to calculate as a function of

text: p[H

text: ]. When [H] is known, the free concentration [A] is calculated from the mass-balance equation in A.

text: Fischer–Tropsch iron catalysts need alkali promotion to attain high activity and stability (e.g. 0.5 wt% ). Addition of Cu for reduction promotion, addition of ,  for structural promotion and maybe some manganese can be applied for selectivity control (e.g. high olefinicity). The working catalyst is only obtained when—after reduction with hydrogen—in the initial period of synthesis several iron carbide phases and elemental carbon are formed whereas iron oxides are still present in addition to some metallic iron. With iron catalysts two directions of selectivity have been pursued. One direction has aimed at a low-molecular-weight olefinic hydrocarbon mixture to be produced in an entrained phase or fluid bed process (Sasol–Synthol process). Due to the relatively high reaction temperature (approx. 340 °C), the average molecular weight of the product is so low that no liquid product phase occurs under reaction conditions. The catalyst particles moving around in the reactor are small (particle diameter 100 µm) and carbon deposition on the catalyst does not disturb reactor operation. Thus a low catalyst porosity with small pore diameters as obtained from fused magnetite (plus promoters) after reduction with hydrogen is appropriate. For maximising the overall gasoline yield, C and C alkenes have been oligomerized at Sasol. However, recovering the olefins for use as chemicals in, e.g., polymerization processes is advantageous today. The second direction of iron catalyst development has aimed at highest catalyst activity to be used at low reaction temperature where most of the hydrocarbon product is in the liquid phase under reaction conditions. Typically, such catalysts are obtained through precipitation from nitrate solutions. A high content of a carrier provides mechanical strength and wide pores for easy mass transfer of the reactants in the liquid product filling the pores. The main product fraction then is a paraffin wax, which is refined to marketable wax materials at Sasol; however, it also can be very selectively hydrocracked to a high quality diesel fuel. Thus, iron catalysts are very flexible.

text: C-terminus - C4 photosynthesis - cadherin - calbindin -calcitonin - calcitonin gene-related peptide - calcitonin gene-related peptide receptor - calcitonin receptor - calcitriol receptor - calcium channel - calcium signaling - calcium-binding protein - Calmodulin - calmodulin-binding protein - Calvin cycle - CAM photosynthesis - CAM plants - cancer - capsid - Carbohydrate - Carbon - Carbon fixation - Carboxylic acid - carcinoembryonic antigen - carrier - carrier protein - CAS registry number - casein - catabolism - catalyst - catalytic domain - CCR5 receptor - CD4 antigen - CD45 antigen - CD95 antigen - CDC28 protein kinase - cell - cell adhesion molecule - Cell biology - cell cycle protein - cell membrane - cell membrane transport - cell nucleus - cell surface receptor - cellular respiration - cellulose - centriole - centromere - centrosome - Chaperone - Chelation - Chemical bond - Chemical compound - Conformation - chemical element - Chemical equilibrium - Chemical formula - Chemical nomenclature - Chemical property - Chemical reaction - Chemical series - Chemical thermodynamics - Cheminformatics - chemiosmosis - chemiosmotic hypothesis - chemiosmotic potential - Chemist - Chemistry - Chemistry basic topics - chemotroph - chemokine receptor - chemoreceptor - chiasma - Chimera (protein) - chimeric protein - Chirality - chloride channel - chlorophyll - chloroplast - chloroplast membrane - cholecystokinin receptor - cholesterine - cholinergic receptor - chorionic gonadotropin - chromatid - chromatin - ciclosporin - Chromatography - Chromosomal crossover - chromosome - chromosome walking - cilium - circular dichroism -  - cis face - Citric acid - Citric acid cycle - cladistics - cloning - coenzyme - cofactor (biochemistry) - colchicine - collagen - colloid - colony-stimulating factor - Colony stimulating factor 1 receptor - Colorimeter - comparative biochemistry - competitive inhibition - complement 3A - complement 5A - complement factor B - complement membrane attack complex - complement receptor - complex - computational biology - computational chemistry - computational genomics - concanavalin A - Concentration - concentration gradient - consensus sequence - conserved sequence - Cooperative - Cooperative binding - Cooperativity - cooperativity cellular respiration - corticotropin - corticotropin receptor - corticotropin-releasing hormone - corticotropin-releasing hormone receptor - cotransport metabolism - covalent bond - Covalent radius - CpG island - cristae - cryptobiology - Crystal structure - Crystallography - cuticula - CXCR4 receptor - cyclic AMP receptor - cyclic AMP receptor protein - cyclic AMP-responsive DNA-binding protein - cyclic electron flow - Cyclic nucleotide - cyclic peptide - cyclin - cyclin A - cyclin B - cyclin E - cyclin-dependent kinase - cycloleucine - cyclosporin - cyclosporine - cystatin - cysteine - cystic fibrosis transmembrane conductance regulator - cytochrome B - cytochrome C - cytochrome P-450 - cytochrome P-450 CYP1A1 - cytochrome C oxidase - cytokine receptor - cytoplasm - cytoplasmic and nuclear receptor - Cytosine - cytoskeletal protein - cytoskeleton - cytosol - cytotoxic T cell -

text: C-terminus

text: C4 photosynthesis

text: cadherin

text: calbindin

text: calcitonin

text: calcitonin gene-related peptide

text: calcitonin gene-related peptide receptor

text: calcitonin receptor

text: calcitriol receptor

text: calcium channel

text: calcium signaling

text: calcium-binding protein

text: Calmodulin

text: calmodulin-binding protein

text: Calvin cycle

text: CAM photosynthesis

text: CAM plants

text: cancer

text: capsid

text: Carbohydrate

text: Carbon

text: Carbon fixation

text: Carboxylic acid

text: carcinoembryonic antigen

text: carrier

text: carrier protein

text: CAS registry number

text: casein

text: catabolism

text: catalyst

text: catalytic domain

text: CCR5 receptor

text: CD4 antigen

text: CD45 antigen

text: CD95 antigen

text: CDC28 protein kinase

text: cell

text: cell adhesion molecule

text: Cell biology

text: cell cycle protein

text: cell membrane

text: cell membrane transport

text: cell nucleus

text: cell surface receptor

text: cellular respiration

text: cellulose

text: centriole

text: centromere

text: centrosome

text: Chaperone

text: Chelation

text: Chemical bond

text: Chemical compound

text: Conformation

text: chemical element

text: Chemical equilibrium

text: Chemical formula

text: Chemical nomenclature

text: Chemical property

text: Chemical reaction

text: Chemical series

text: Chemical thermodynamics

text: Cheminformatics

text: chemiosmosis

text: chemiosmotic hypothesis

text: chemiosmotic potential

text: Chemist

text: Chemistry

text: Chemistry basic topics

text: chemotroph

text: chemokine receptor

text: chemoreceptor

text: chiasma

text: Chimera (protein)

text: chimeric protein

text: Chirality

text: chloride channel

text: chlorophyll

text: chloroplast

text: chloroplast membrane

text: cholecystokinin receptor

text: cholesterine

text: cholinergic receptor

text: chorionic gonadotropin

text: chromatid

text: chromatin

text: ciclosporin

text: Chromatography

text: Chromosomal crossover

text: chromosome

text: chromosome walking

text: cilium

text: circular dichroism

text: cis face

text: Citric acid

text: Citric acid cycle

text: cladistics

text: cloning

text: coenzyme

text: cofactor (biochemistry)

text: colchicine

text: collagen

text: colloid

text: colony-stimulating factor

text: Colony stimulating factor 1 receptor

text: Colorimeter

text: comparative biochemistry

text: competitive inhibition

text: complement 3A

text: complement 5A

text: complement factor B

text: complement membrane attack complex

text: complement receptor

text: complex

text: computational biology

text: computational chemistry

text: computational genomics

text: concanavalin A

text: Concentration

text: concentration gradient

text: consensus sequence

text: conserved sequence

text: Cooperative

text: Cooperative binding

text: Cooperativity

text: cooperativity cellular respiration

text: corticotropin

text: corticotropin receptor

text: corticotropin-releasing hormone

text: corticotropin-releasing hormone receptor

text: cotransport metabolism

text: covalent bond

text: Covalent radius

text: CpG island

text: cristae

text: cryptobiology

text: Crystal structure

text: Crystallography

text: cuticula

text: CXCR4 receptor

text: cyclic AMP receptor

text: cyclic AMP receptor protein

text: cyclic AMP-responsive DNA-binding protein

text: cyclic electron flow

text: Cyclic nucleotide

text: cyclic peptide

text: cyclin

text: cyclin A

text: cyclin B

text: cyclin E

text: cyclin-dependent kinase

text: cycloleucine

text: cyclosporin

text: cyclosporine

text: cystatin

text: cysteine

entity_name: Cystic fibrosis transmembrane conductance regulator

text: cystic fibrosis transmembrane conductance regulator

text: cytochrome B

text: cytochrome C

text: cytochrome P-450

text: cytochrome P-450 CYP1A1

text: cytochrome C oxidase

text: cytokine receptor

text: cytoplasm

text: cytoplasmic and nuclear receptor

text: Cytosine

text: cytoskeletal protein

text: cytoskeleton

text: cytosol

text: cytotoxic T cell

text: the  "chemical affinity" or "reaction force" between A and B did not just depend on the chemical nature of the reactants, as had previously been supposed, but also depended on the amount of each reactant in a reaction mixture. Thus the Law of Mass Action was first stated as follows:

text: He started by detailed experimental work on the formation of hydrogen iodide. His technique was to mix hydrogen and iodine in a sealed tube, which he placed in a thermostat and held at a constant high temperature. The reaction eventually reached an equilibrium, at which the rate of formation of hydrogen iodide was equal to the rate of decomposition to the original reaction (H + I ≡ 2HI). The equilibrium mixture of hydrogen, iodine, and hydrogen iodide was frozen by rapid cooling, and the amount of hydrogen iodide present could be analyzed. Using different amounts of initial reactants, Bodenstein could vary the amounts present at equilibrium and verify the law of chemical equilibrium proposed in 1863 by Cato Maximilian Guldberg and Peter Waage. His work, published in 1899, was one of the first equilibrium investigations over an extended temperature range.

text: He started by detailed experimental work on the formation of hydrogen iodide. His technique was to mix hydrogen and iodine in a sealed tube, which he placed in a thermostat and held at a constant high temperature. The reaction eventually reached an

text: equilibrium

text: , at which the rate of formation of hydrogen iodide was equal to the rate of decomposition to the original reaction (H + I ≡ 2HI). The equilibrium mixture of hydrogen, iodine, and hydrogen iodide was frozen by rapid cooling, and the amount of hydrogen iodide present could be analyzed. Using different amounts of initial reactants, Bodenstein could vary the amounts present at equilibrium and verify the law of chemical equilibrium proposed in 1863 by

text: Cato Maximilian Guldberg

text: and

text: Peter Waage

text: . His work, published in 1899, was one of the first equilibrium investigations over an extended temperature range.

text: The equilibrium of the reaction is dependent on the concentrations of the reactants, the solvent and the temperature. The necessary quantity of urea for the formation of inclusion compounds varies from about 1 to 0.8 mole of urea per methyl- and methylene group in a carbon chain. The urea is added as a supersaturated aqueous solution to compensate for losses due to adduct formation during the process. In order to avoid a too high concentrations of adducts in the dewaxed oil a solvent such as methyl isobutyl ketone or methylene chloride is used for dilution. The ratio of oil to water phase is about 1 to 0.5. The mixing of the oil and water phases occurs at slightly elevated temperatures of about 35 °C. In the course of the reaction the mixture is cooled to room temperature. Lower temperatures are advantageous for the formation of inclusion complexes.

text: The equilibrium of the reaction is dependent on the concentrations of the reactants, the solvent and the temperature. The necessary quantity of urea for the formation of inclusion compounds varies from about 1 to 0.8 mole of urea per methyl- and methylene group in a carbon chain. The urea is added as a

text: supersaturated

text: aqueous solution to compensate for losses due to adduct formation during the process. In order to avoid a too high concentrations of adducts in the dewaxed oil a

text: solvent

text: such as

text: methyl isobutyl ketone

text: or

text: methylene chloride

text: is used for dilution. The ratio of oil to water phase is about 1 to 0.5. The mixing of the oil and water phases occurs at slightly elevated temperatures of about 35 °C. In the course of the reaction the mixture is cooled to room temperature. Lower temperatures are advantageous for the formation of inclusion complexes.

text: The eruption is caused by a physical reaction, rather than any chemical reaction. The addition of the Mentos leads to the rapid nucleation of carbon dioxide gas bubbles precipitating out of solution. Gasses, in general, are more soluble in liquids at elevated pressures. Carbonated sodas contain elevated levels of carbon dioxide under pressure. The solution becomes supersaturated with carbon dioxide when the bottle is opened, and the pressure is released. Under these conditions, carbon dioxide begins to precipitate from solution, forming gas bubbles. Normally, this process is relatively slow, because the activation energy for this process is high. The activation energy for a process like bubble nucleation depends on where the bubble forms. It is highest for bubbles that form in the liquid itself (homogeneous nucleation), and lower if the bubble forms on some other surface (heterogeneous nucleation). When the pressure is released from a soda bottle, the bubbles tend to form on the sides of the bottle. But because they are smooth and clean, the activation energy is still relatively high, and the process is slow. The addition of other nucleation sites provides an alternate pathway for the reaction to occur with lower activation energy, much like a catalyst. For instance dropping grains of salt or sand into the solution lowers the activation energy, and increases the rate of carbon dioxide precipitation. The physical characteristics of Mentos (surface roughness, easy dissolution into the liquid, etc.) have the effect of drastically reducing the activation energy for carbon dioxide bubble formation, so that the nucleation rate becomes exceedingly high. This formation of gaseous carbon dioxide within the water, which due to hydrogen bonding and its high surface tension wants to maintain a connected matrix of molecules, causes the water to foam, ultimately generating the "jet"—or "geyser"—or eruption-like nature of the effusion. The foaming is aided by the presence of chemicals like potassium benzoate and aspartame in Diet Coke, and gelatin and gum arabic in the Mentos candy, all which influence the nature of water's surface tension and degree to which it can foam.

text: The eruption is caused by a physical reaction, rather than any chemical reaction. The addition of the Mentos leads to the rapid

text: nucleation

text: of

text: carbon dioxide

text: gas bubbles

text: precipitating

text: out of solution. Gasses, in general, are more

text: soluble

text: in liquids at elevated pressures. Carbonated sodas contain elevated levels of carbon dioxide under pressure. The solution becomes

text: supersaturated

text: with carbon dioxide when the bottle is opened, and the pressure is released. Under these conditions, carbon dioxide begins to precipitate from solution, forming gas bubbles. Normally, this process is relatively slow, because the

text: activation energy

text: for this process is high. The activation energy for a process like bubble nucleation depends on where the bubble forms. It is highest for bubbles that form in the liquid itself (homogeneous nucleation), and lower if the bubble forms on some other surface (

text: heterogeneous nucleation

text: ). When the pressure is released from a soda bottle, the bubbles tend to form on the sides of the bottle. But because they are smooth and clean, the activation energy is still relatively high, and the process is slow. The addition of other nucleation sites provides an alternate pathway for the reaction to occur with lower activation energy, much like a catalyst. For instance dropping grains of salt or sand into the solution lowers the activation energy, and increases the rate of carbon dioxide precipitation. The physical characteristics of Mentos (surface roughness, easy

text: dissolution

text: into the liquid, etc.) have the effect of drastically reducing the activation energy for carbon dioxide bubble formation, so that the nucleation rate becomes exceedingly high. This formation of gaseous carbon dioxide within the water, which due to

text: hydrogen bonding

text: and its high

text: surface tension

text: wants to maintain a connected matrix of molecules, causes the water to

text: foam

text: , ultimately generating the "jet"—or "geyser"—or eruption-like nature of the effusion. The foaming is aided by the presence of chemicals like

text: potassium benzoate

text: and

text: aspartame

text: in Diet Coke, and

text: gelatin

text: and

text: gum arabic

text: in the Mentos candy, all which influence the nature of water's surface tension and degree to which it can foam.

text: In the presence of a catalyst, less free energy is required to reach the transition state, but the total free energy from reactants to products does not change. A catalyst may participate in multiple chemical transformations. The effect of a catalyst may vary due to the presence of other substances known as inhibitors or poisons (which reduce the catalytic activity) or promoters (which increase the activity). The opposite of a catalyst, a substance that reduces the rate of a reaction, is an inhibitor.

text: In the presence of a catalyst, less

text: free energy

text: is required to reach the

text: transition state

text: , but the total free energy from reactants to products does not change. A catalyst may participate in multiple chemical transformations. The effect of a catalyst may vary due to the presence of other substances known as inhibitors or

text: poisons

text: (which reduce the catalytic activity) or promoters (which increase the activity). The opposite of a catalyst, a substance that reduces the rate of a reaction, is an

text: inhibitor

text: This model of the chemical reactions makes several predictions that were examined in experiments published by Jerry Goodisman in 2001. Goodisman notes that numerous recent authors propose chemical reactions for the lemon battery that involve dissolution of the copper electrode into the electrolyte. Goodman excludes this reaction as being inconsistent with the experiments, and notes that the correct chemistry, which involves the evolution of hydrogen at the copper electrode, has been known for many years. Most of the detailed predictions of the model apply to the battery's voltage that is measured directly by a meter; nothing else is connected to the battery. When the electrolyte was modified by adding zinc sulfate (ZnSO), the voltage from the cell was reduced as predicted using the Nernst equation for the model. The Nernst equation essentially says how much the voltage drops as more zinc sulfate is added. The addition of copper sulfate (CuSO) did not affect the voltage. This result is consistent with the fact that copper atoms from the electrode are not involved in the chemical reaction model for the cell.

text: This model of the chemical reactions makes several predictions that were examined in experiments published by Jerry Goodisman in 2001. Goodisman notes that numerous recent authors propose chemical reactions for the lemon battery that involve dissolution of the copper electrode into the electrolyte. Goodman excludes this reaction as being inconsistent with the experiments, and notes that the correct chemistry, which involves the evolution of hydrogen at the copper electrode, has been known for many years. Most of the detailed predictions of the model apply to the battery's voltage that is measured directly by a meter; nothing else is connected to the battery. When the electrolyte was modified by adding zinc sulfate (ZnSO), the voltage from the cell was reduced as predicted using the

text: Nernst equation

text: for the model. The Nernst equation essentially says how much the voltage drops as more zinc sulfate is added. The addition of copper sulfate (CuSO) did not affect the voltage. This result is consistent with the fact that copper atoms from the electrode are not involved in the chemical reaction model for the cell.

text: Heterogeneous catalysts act in a different phase than the reactants. Most heterogeneous catalysts are solids that act on substrates in a liquid or gaseous reaction mixture. Diverse mechanisms for reactions on surfaces are known, depending on how the adsorption takes place (Langmuir-Hinshelwood, Eley-Rideal, and Mars-van Krevelen). The total surface area of solid has an important effect on the reaction rate. The smaller the catalyst particle size, the larger the surface area for a given mass of particles.

text: Heterogeneous catalysts act in a different

text: phase

text: than the

text: reactants

text: . Most heterogeneous catalysts are

text: solid

text: s that act on substrates in a

text: liquid

text: or gaseous

text: reaction mixture

text: . Diverse mechanisms for

text: reactions on surfaces

text: are known, depending on how the adsorption takes place (

text: Langmuir-Hinshelwood

text: Eley-Rideal

text: , and Mars-van Krevelen). The total surface area of solid has an important effect on the reaction rate. The smaller the catalyst particle size, the larger the surface area for a given mass of particles.

text: With only 75 natural metals in existence (and not all of these showing extensive catalytic activities) the design of new catalysts is very much dominated by the development of new classes of ligands. Certain ligands, often referred to as 'privileged ligands', have been found to be effective in a wide range of reactions; examples include BINOL, Salen and BOX. However, most catalysts are rarely general, requiring certain functional groups in the substrate to form the transition state complex correctly: arbitrary structures cannot be used. For example, Noyori asymmetric hydrogenation with BINAP/Ru requires a β-ketone, although another catalyst, BINAP/diamine-Ru, widens the scope to α,β-olefins and aromatics.

text: With only 75 natural metals in existence (and not all of these showing extensive catalytic activities) the design of new catalysts is very much dominated by the development of new classes of

text: ligand

text: s. Certain ligands, often referred to as '

text: privileged ligand

text: s', have been found to be effective in a wide range of reactions; examples include

text: BINOL

text: Salen

text: and

text: BOX

text: . However, most catalysts are rarely general, requiring certain functional groups in the substrate to form the transition state complex correctly: arbitrary structures cannot be used. For example,

text: Noyori asymmetric hydrogenation

text: with BINAP/Ru requires a β-ketone, although another catalyst, BINAP/diamine-Ru, widens the scope to α,β-olefins and aromatics.

text: In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. In catalysed photolysis, light is absorbed by an adsorbed substrate. In photogenerated catalysis, the photocatalytic activity (PCA) depends on the ability of the catalyst to create electron–hole pairs, which generate free radicals (e.g. hydroxyl radicals: •OH) able to undergo secondary reactions. Its practical application was made possible by the discovery of water electrolysis by means of titanium dioxide.The commercially used process is called the advanced oxidation process (AOP). There are several ways the AOP can be carried out; these may (but do not necessarily) involve TiO or even the use of UV light. Generally the defining factor is the production and use of the hydroxyl radical.

text: In

text: chemistry

text: , photocatalysis is the acceleration of a

text: photoreaction

text: in the presence of a

text: catalyst

text: . In catalysed

text: photolysis

text: light

text: is absorbed by an

text: adsorbed

text: substrate. In photogenerated catalysis, the photocatalytic activity (PCA) depends on the ability of the catalyst to create

text: electron–hole pairs

text: , which generate

text: free radical

text: s (e.g.

text: hydroxyl radical

text: s: •OH) able to undergo secondary reactions. Its practical application was made possible by the discovery of

text: water

text: electrolysis

text: by means of

text: titanium dioxide

text: .The commercially used process is called the

text: advanced oxidation process

text: (AOP). There are several ways the AOP can be carried out; these may (but do not necessarily) involve TiO or even the use of UV light. Generally the defining factor is the production and use of the

text: hydroxyl

text: radical

text: In a conventional chemical rocket engine the rocket carries with itself in flight both its fuel and its oxidizer.  The chemical reaction between the fuel and the oxidizer produces reactant products which are nominally gasses at the pressures and temperatures in the rocket's  combustion chamber.  The reaction is also highly energetic (exothermic) releasing tremendous energy in the form of heat; that is imparted to the reactant products in the combustion chamber giving this mass enormous internal energy which, when expanded through a nozzle is capable of producing very high exhaust velocities. The exhaust is directed rearward through the nozzle, thereby producing a thrust forward.

text: In a conventional chemical rocket engine the rocket carries with itself in flight both its fuel and its

text: oxidizer

text: .  The chemical reaction between the fuel and the oxidizer produces reactant products which are nominally gasses at the pressures and temperatures in the rocket's  combustion chamber.  The reaction is also highly energetic (exothermic) releasing tremendous energy in the form of heat; that is imparted to the reactant products in the combustion chamber giving this mass enormous internal energy which, when expanded through a

text: nozzle

text: is capable of producing very high exhaust velocities. The exhaust is directed rearward through the nozzle, thereby producing a thrust forward.

text: Chemical chain reactions were first proposed by German chemist Max Bodenstein in 1913, and were reasonably well understood before nuclear chain reactions were proposed. It was understood that chemical chain reactions were responsible for exponentially increasing rates in reactions, such as produced chemical explosions.

text: Chemical

text: chain reaction

text: s were first proposed by German chemist

text: Max Bodenstein

text: in 1913, and were reasonably well understood before nuclear chain reactions were proposed. It was understood that chemical chain reactions were responsible for exponentially increasing rates in reactions, such as produced chemical explosions.

text: Reactions can take place between two solids. However, because of the relatively small diffusion rates in solids, the corresponding chemical reactions are very slow in comparison to liquid and gas phase reactions. They are accelerated by increasing the reaction temperature and finely dividing the reactant to increase the contacting surface area.

text: Reactions can take place between two solids. However, because of the relatively small

text: diffusion

text: rates in solids, the corresponding chemical reactions are very slow in comparison to liquid and gas phase reactions. They are accelerated by increasing the reaction temperature and finely dividing the reactant to increase the contacting surface area.

text: Alanopine dehydrogenase () is an enzyme that catalyzes the chemical reaction

text: Alanopine dehydrogenase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: A reaction inhibitor is a substance that decreases the rate of, or prevents, a chemical reaction.A catalyst, in contrast, is a substance that increases the rate of a chemical reaction.

text: A reaction inhibitor is a

text: substance

text: that decreases the rate of, or prevents, a

text: chemical reaction

text: .A catalyst, in contrast, is a substance that increases the rate of a chemical reaction.

text: Steam serves several roles in this reaction.  It is the source of heat for powering the endothermic reaction, and it removes coke that tends to form on the iron oxide catalyst through the water gas shift reaction.  The potassium promoter enhances this decoking reaction.  The steam also dilutes the reactant and products, shifting the position of chemical equilibrium towards products.  A typical styrene plant consists of two or three reactors in series, which operate under vacuum to enhance the conversion and selectivity.  Typical per-pass conversions are ca. 65% for two reactors and 70-75% for three reactors.  Selectivity to styrene is 93-97%.  The main byproducts are benzene and toluene.  Because styrene and ethylbenzene have similar boiling points (145 and 136 °C, respectively), their separation requires tall distillation towers and high return/reflux ratios.  At its distillation temperatures, styrene tends to polymerize.  To minimize this problem, early styrene plants added elemental sulfur to inhibit the polymerization.  During the 1970s, new free radical inhibitors consisting of nitrated phenol-based retarders were developed.  More recently, a number of additives have been developed that exhibit superior inhibition against polymerization. However, the nitrated phenols are still widely used because of their relatively low cost.  These reagents are added prior to the distillation.

text: Steam serves several roles in this reaction.  It is the source of heat for powering the

text: endothermic

text: reaction, and it removes coke that tends to form on the iron oxide catalyst through the

text: water gas shift reaction

text: .  The potassium promoter enhances this decoking reaction.  The steam also dilutes the reactant and products, shifting the position of

text: chemical equilibrium

text: towards products.  A typical styrene plant consists of two or three reactors in series, which operate under vacuum to enhance the conversion and selectivity.  Typical per-pass conversions are ca. 65% for two reactors and 70-75% for three reactors.  Selectivity to styrene is 93-97%.  The main byproducts are benzene and

text: toluene

text: .  Because styrene and ethylbenzene have similar boiling points (145 and 136 °C, respectively), their separation requires tall

text: distillation tower

text: s and high return/reflux ratios.  At its distillation temperatures, styrene tends to polymerize.  To minimize this problem, early styrene plants added elemental sulfur to inhibit the polymerization.  During the 1970s, new free radical inhibitors consisting of nitrated

text: phenol

text: -based retarders were developed.  More recently, a number of additives have been developed that exhibit superior inhibition against polymerization. However, the nitrated phenols are still widely used because of their relatively low cost.  These reagents are added prior to the distillation.

text: For thermally robust materials, high temperature methods are often employed.  For example, bulk solids are prepared using tube furnaces, which allow reactions to be conducted up to ca. 1100 °C. Special equipment e.g. ovens consisting of a tantalum tube through which an electric current is passed can be used for even higher temperatures up to 2000 °C. Such high temperatures are at times required to induce diffusion of the reactants, but this depends strongly on the system studied. Some solid state reactions already proceed at temperatures as low as 100 °C.

text: For thermally robust materials, high temperature methods are often employed.  For example, bulk solids are prepared using

text: tube furnace

text: s, which allow reactions to be conducted up to ca. 1100 °C. Special equipment e.g. ovens consisting of a tantalum tube through which an electric current is passed can be used for even higher temperatures up to 2000 °C. Such high temperatures are at times required to induce diffusion of the reactants, but this depends strongly on the system studied. Some solid state reactions already proceed at temperatures as low as 100 °C.

text: where X is the reactant (kerogen) and κ is the reaction rate constant which introduces the temperature-dependence via the Arrhenius equation.

text: where X is the reactant (kerogen) and κ is the

text: reaction rate constant

text: which introduces the temperature-dependence via the

text: Arrhenius equation

text: With the writings of Théophile de Donder as precedent, Ilya Prigogine and Defay in Chemical Thermodynamics (1954) defined chemical affinity as the rate of change of the uncompensated heat of reaction Q as the reaction progress variable or reaction extent ξ grows infinitesimally:

text: With the writings of

text: Théophile de Donder

text: as precedent,

text: Ilya Prigogine

text: and Defay in Chemical Thermodynamics (1954) defined chemical affinity as the rate of change of the uncompensated

text: heat

text: of reaction Q as the

text: reaction progress variable

text: or reaction extent ξ grows infinitesimally:

text: In enzymology, a lysyltransferase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , a lysyltransferase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: The mechanism of the Suzuki reaction is best viewed from the perspective of the palladium catalyst.  The first step is the oxidative addition of palladium to the halide 2 to form the organopalladium species 3.  Reaction with base gives intermediate 4, which via transmetalation with the boron-ate complex 6  (produced by reaction of the boronic acid 5 with base) forms the organopalladium species 8.  Reductive elimination of the desired product 9 restores the original palladium catalyst 1 which completes the catalytic cycle. The Suzuki coupling takes place in the presence of a base and for a long time the role of the base was never fully understood. The base was first believed to form a trialkyl borate (RB-OR), in the case of a reaction of an trialkylborane (BR) and alkoxide (OR); this species could be considered as being more nucleophilic and then more reactive towards the palladium complex present in the transmetalation step. Duc and coworkers investigated the role of the base in the reaction mechanism for the Suzuki coupling and they found that the base has three roles: Formation of the palladium complex [ArPd(OR)L], formation of the trialkyl borate and the acceleration of the reductive elimination step by reaction of the alkoxide with the palladium complex.

text: The

text: mechanism

text: of the Suzuki reaction is best viewed from the perspective of the palladium catalyst.  The first step is the

text: oxidative addition

text: of palladium to the

text: halide

text: 2 to form the

text: organopalladium

text: species 3.  Reaction with base gives

text: intermediate

text: 4, which via

text: transmetalation

text: with the boron-

text: ate complex

text: 6  (produced by reaction of the boronic acid 5 with base) forms the

text: organopalladium

text: species 8.

text: Reductive elimination

text: of the desired product 9 restores the original palladium catalyst 1 which completes the

text: catalytic cycle

text: . The Suzuki coupling takes place in the presence of a base and for a long time the role of the base was never fully understood. The base was first believed to form a trialkyl borate (RB-OR), in the case of a reaction of an trialkylborane (BR) and

text: alkoxide

text: (OR); this species could be considered as being more

text: nucleophilic

text: and then more reactive towards the palladium complex present in the transmetalation step. Duc and coworkers investigated the role of the base in the reaction mechanism for the Suzuki coupling and they found that the base has three roles: Formation of the palladium complex [ArPd(OR)L], formation of the trialkyl borate and the acceleration of the reductive elimination step by reaction of the alkoxide with the palladium complex.

text: If the concentration of a reactant remains constant (because it is a catalyst or it is in great excess with respect to the other reactants), its concentration can be included in the rate constant, obtaining a pseudo–first-order (or occasionally pseudo–second-order) rate equation. For a typical second-order reaction with rate equation r = k[A][B], if the concentration of reactant B is constant then r = k[A][B] = k'[A], where the pseudo–first-order rate constant k' = k[B]. The second-order rate equation has been reduced to a pseudo–first-order rate equation, which makes the treatment to obtain an integrated rate equation much easier.

text: If the concentration of a reactant remains constant (because it is a

text: catalyst

text: or it is in great excess with respect to the other reactants), its concentration can be included in the rate constant, obtaining a pseudo–first-order (or occasionally pseudo–second-order) rate equation. For a typical second-order reaction with rate equation r = k[A][B], if the concentration of reactant B is constant then r = k[A][B] = k'[A], where the pseudo–first-order rate constant k' = k[B]. The second-order rate equation has been reduced to a pseudo–first-order rate equation, which makes the treatment to obtain an integrated rate equation much easier.

text: A catalyst is a substance that alters the rate of a chemical reaction but remains chemically unchanged afterwards. The catalyst increases the rate of the reaction by providing a different reaction mechanism to occur with a lower activation energy. In autocatalysis a reaction product is itself a catalyst for that reaction leading to positive feedback. Proteins that act as catalysts in biochemical reactions are called enzymes. Michaelis–Menten kinetics describe the rate of enzyme mediated reactions. A catalyst does not affect the position of the equilibrium, as the catalyst speeds up the backward and forward reactions equally.

text: A

text: catalyst

text: is a substance that alters the rate of a chemical reaction but remains

text: chemically

text: unchanged afterwards. The catalyst increases the rate of the reaction by providing a different

text: reaction mechanism

text: to occur with a lower

text: activation energy

text: . In

text: autocatalysis

text: a reaction product is itself a catalyst for that reaction leading to

text: positive feedback

text: . Proteins that act as catalysts in biochemical reactions are called

text: enzyme

text: s.

text: Michaelis–Menten kinetics

text: describe the

text: rate of enzyme mediated reactions

text: . A catalyst does not affect the position of the equilibrium, as the catalyst speeds up the backward and forward reactions equally.

text: The most important points on a PES are the stationary points where the surface is flat, i.e. parallel to a horizontal line corresponding to one geometric parameter, a plane corresponding to two such parameters or even a hyper-plane corresponding to more than two geometric parameters. The energy values corresponding to the transition states and the ground state of the reactants and products can be found using the potential energy function by calculating the function's critical points or the stationary points.  Stationary points occur when 1st partial derivative of the energy with respect to each geometric parameter is equal to zero.

text: The most important points on a PES are the

text: stationary points

text: where the surface is flat, i.e. parallel to a horizontal line corresponding to one geometric parameter, a plane corresponding to two such parameters or even a hyper-plane corresponding to more than two geometric parameters. The energy values corresponding to the transition states and the ground state of the reactants and products can be found using the potential energy function by calculating the function's critical points or the stationary points.  Stationary points occur when 1st partial derivative of the energy with respect to each geometric parameter is equal to zero.

text: The principle can be shown graphically by plotting the reaction rate against a property such as the heat of adsorption of the reactant by the catalyst. Such plots pass through a maximum, looking roughly like a triangle or an inverted parabola, and are called volcano plots because of their shape. Analogous three-dimensional plots can also be built against two different properties, such as the heats of adsorption of the two reactants for a two-component reaction. In that case the plot is generally shown as a contour plot and is called a volcano surface. Volcano plots were introduced by Balandin.

text: The principle can be shown graphically by plotting the

text: reaction rate

text: against a property such as the

text: heat of adsorption

text: of the reactant by the catalyst. Such plots pass through a maximum, looking roughly like a triangle or an inverted parabola, and are called volcano plots because of their shape. Analogous three-dimensional plots can also be built against two different properties, such as the heats of adsorption of the two reactants for a two-component reaction. In that case the plot is generally shown as a

text: contour plot

text: and is called a volcano surface. Volcano plots were introduced by Balandin.

text: The rate law or rate equation for a chemical reaction is a differential equation that links the reaction rate with concentrations or pressures of reactants and constant parameters (normally rate coefficients and partial reaction orders). To determine the rate equation for a particular system one combines the reaction rate with a mass balance for the system.

text: The rate law or

text: rate equation

text: for a

text: chemical reaction

text: is a differential equation that links the

text: reaction rate

text: reaction order

text: s). To determine the rate equation for a particular system one combines the reaction rate with a

text: mass balance

text: for the system.

text: To evaluate the usefulness of these reactions, in addition to the reactants, the products, and the energy released, one needs to know something about the cross section. Any given fusion device has a maximum plasma pressure it can sustain, and an economical device would always operate near this maximum. Given this pressure, the largest fusion output is obtained when the temperature is chosen so that <σv>/T is a maximum. This is also the temperature at which the value of the triple product nTτ required for ignition is a minimum, since that required value is inversely proportional to <σv>/T (see Lawson criterion). (A plasma is "ignited" if the fusion reactions produce enough power to maintain the temperature without external heating.) This optimum temperature and the value of <σv>/T at that temperature is given for a few of these reactions in the following table.

text: To evaluate the usefulness of these reactions, in addition to the reactants, the products, and the energy released, one needs to know something about the cross section. Any given fusion device has a maximum plasma pressure it can sustain, and an economical device would always operate near this maximum. Given this pressure, the largest fusion output is obtained when the temperature is chosen so that <σv>/T is a maximum. This is also the temperature at which the value of the triple product nTτ required for

text: ignition

text: is a minimum, since that required value is inversely proportional to <σv>/T (see

text: Lawson criterion

text: ). (A plasma is "ignited" if the fusion reactions produce enough power to maintain the temperature without external heating.) This optimum temperature and the value of <σv>/T at that temperature is given for a few of these reactions in the following table.

text: A unit operation is a physical step in an individual chemical engineering process. Unit operations (such as crystallization, filtration, drying and evaporation) are used to prepare reactants, purifying and separating its products, recycling unspent reactants, and controlling energy transfer in reactors. On the other hand, a unit process is the chemical equivalent of a unit operation. Along with unit operations, unit processes constitute a process operation. Unit processes (such as nitration and oxidation) involve the conversion of material by biochemical, thermochemical and other means. Chemical engineers responsible for these are called process engineers.

text: A unit operation is a physical step in an individual chemical engineering process. Unit operations (such as

text: crystallization

text: filtration

text: drying

text: and

text: evaporation

text: ) are used to prepare reactants, purifying and separating its products, recycling unspent reactants, and controlling energy transfer in reactors. On the other hand, a unit process is the chemical equivalent of a unit operation. Along with unit operations, unit processes constitute a process operation. Unit processes (such as

text: nitration

text: and

text: oxidation

text: ) involve the conversion of material by

text: biochemical

text: thermochemical

text: and other means. Chemical engineers responsible for these are called process engineers.

text: The parish church was originally dedicated to Saint Veep, but when it was rebuilt in 1336 it was rededicated to Saint Quiricus and Saint Julietta.

text: The parish church was originally dedicated to Saint Veep, but when it was rebuilt in 1336 it was rededicated to

text: Saint Quiricus and Saint Julietta

text: In enzymology, an uronolactonase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , an uronolactonase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: In Los Angeles, working class waitress Eva Sanchez returns home to her daughter Cali and terminally ill father Rico, who also despises the New Founding Fathers. Rico slips out to a waiting limousine, leaving a note for his family revealing that he has sold himself as a Purge offering in exchange for $100,000 to be paid to Eva and Cali following the Purge.

text: In Los Angeles, working class

text: waitress

text: Eva Sanchez returns home to her daughter Cali and terminally ill father Rico, who also despises the New Founding Fathers. Rico slips out to a waiting

text: limousine

text: , leaving a note for his family revealing that he has sold himself as a Purge offering in exchange for $100,000 to be paid to Eva and Cali following the Purge.

text: In enzymology, a galactolipase () is an enzyme that catalyzes the chemical reaction

text: In

text: enzymology

text: , a galactolipase () is an

text: enzyme

text: that

text: catalyzes

text: the

text: chemical reaction

text: A reagent  is a substance or compound added to a system to cause a chemical reaction, or added to see if a reaction occurs. The terms reactant and reagent are often used interchangeably—however, a reactant is more specifically a substance consumed in the course of a chemical reaction. Solvents, though involved in the reaction, are usually not called reactants. Similarly, catalysts are not consumed by the reaction, so they are not reactants. In biochemistry, especially in connection with enzyme-catalyzed reactions, the reactants are commonly called substrates.

text: A reagent  is a substance or compound added to a system to cause a chemical reaction, or added to see if a reaction occurs. The terms reactant and reagent are often used interchangeably—however, a reactant is more specifically a substance consumed in the course of a chemical reaction.

text: Solvent

text: s, though involved in the reaction, are usually not called reactants. Similarly,

text: catalysts

text: are not consumed by the reaction, so they are not reactants. In

text: biochemistry

text: , especially in connection with

text: enzyme

text: -catalyzed reactions, the reactants are commonly called

text: substrates

text: Biochemical computers use the immense variety of feedback loops that are characteristic of biological chemical reactions in order to achieve computational functionality. Feedback loops in biological systems take many forms, and many different factors can provide both positive and negative feedback to a particular biochemical process, causing either an increase in chemical output or a decrease in chemical output, respectively. Such factors may include the quantity of catalytic enzymes present, the amount of reactants present, the amount of products present, and the presence of molecules that bind to and thus alter the chemical reactivity of any of the aforementioned factors. Given the nature of these biochemical systems to be regulated through many different mechanisms, one can engineer a chemical pathway comprising a set of molecular components that react to produce one particular product under one set of specific chemical conditions and another particular product under another set of conditions. The presence of the particular product that results from the pathway can serve as a signal, which can be interpreted—along with other chemical signals—as a computational output based upon the starting chemical conditions of the system (the input).

text: Biochemical computers use the immense variety of feedback loops that are characteristic of biological

text: chemical reactions

text: Following the first flights in 1906 some modifications were made: the triangular section keel between the gondolas was extended fore and aft, the biplane elevators were replaced by two sets of quadruple elevators mounted at either end of the cylindrical section of the hull and the rudders were mounted between the tips of the horizontal stabilisers.

text: When a catalyst is involved in the collision between the reactant molecules, less energy is required for the chemical change to take place, and hence more collisions have sufficient energy for reaction to occur. The reaction rate therefore increases.

text: When it is finely divided, as with palladium on carbon, palladium forms a versatile catalyst; it speeds hydrogenation, dehydrogenation, and petroleum cracking. A large number of carbon–carbon bonding reactions in organic chemistry (such as the Heck reaction and Suzuki coupling) are facilitated by palladium compound catalysts. (See Palladium Compounds and palladium-catalyzed coupling reactions.)

text: When it is finely divided, as with

text: palladium on carbon

text: , palladium forms a versatile

text: catalyst

text: ; it speeds

text: hydrogenation

text: dehydrogenation

text: , and

text: petroleum cracking

text: . A large number of

text: carbon–carbon bonding

text: reactions in

text: organic chemistry

text: (such as the

text: Heck reaction

text: and

text: Suzuki coupling

text: ) are facilitated by palladium compound catalysts. (See

text: Palladium Compounds

text: and

text: palladium-catalyzed coupling reactions

text: Love Games is the debut full-length album from Evan Rogers, singer-songwriter-producer and part of the duo of Carl Sturken and Evan Rogers.  In addition to Carl Sturken's contributions, John Nevin (who also would appear on Donny Osmond's 1989 comeback album) appears here on bass; he would resurface in 1991 as part of the Sturken/Rogers R&B/dance-rock band Rythm Syndicate.

text: Love Games is the debut full-length album from Evan Rogers, singer-songwriter-producer and part of the duo of

text: Carl Sturken and Evan Rogers

text: .  In addition to Carl Sturken's contributions, John Nevin (who also would appear on

text: Donny Osmond's 1989 comeback album

text: ) appears here on bass; he would resurface in 1991 as part of the Sturken/Rogers R&B/dance-rock band

text: Rythm Syndicate

text: DNA is the seventh studio album by the American rock band Trapt, released on August 19, 2016. The album's recording was partly funded by a 2014 campaign on Indiegogo. The band was originally set to release the album in 2015. Best Buy offered a Limited Edition, which included the 2 bonus track "Panic Room" and "Chasing Highs", as well as the front cover of the insert sleeve being autographed by the band.

text: Chemical reduction is one half of a redox reaction, which results in the gain of electrons. One of the reactants in the reaction becomes oxidized, or loses electrons, while the other reactant becomes reduced, or gains electrons. In ISCR, reducing compounds, compounds that accept electrons given by other compounds in a reaction, are used to change the contaminants into harmless compounds.

text: Chemical reduction is one half of a

text: redox

text: reaction, which results in the gain of electrons. One of the reactants in the reaction becomes oxidized, or loses electrons, while the other reactant becomes reduced, or gains electrons. In ISCR, reducing compounds, compounds that accept electrons given by other compounds in a reaction, are used to change the contaminants into harmless compounds.

text: The compound is corrosive to most metals. It reacts with iron, evolving carbon tetrachloride.  Perchloromethyl mercaptan is oxidized by nitric acid to trichloromethanesulfonyl chloride (ClCSOCl), a white solid.