Chesnut Chem 1212k Ch 16 Vocabulary

activation energy
(or activation barrier) The kinetic energy that reactant molecules must have to allow them to reach the transition state so that a reaction can occur.
arrhenius equation
An equation that relates the specific rate constant to activation energy and temperature.
catalyst
A substance that increases the rate at which a reaction occurs. It is regenerated during the course of the reaction and can then interact with more reactants to convert them into products.
chemical kinetics
The study of rates and mechanisms of chemical reactions and of the factors on which they depend.
collision theory
A theory of reaction rates that states that effective collisions between reactant molecules must take place for reaction to occur.
effective collision
A collision between molecules that results in reaction; one in which molecules collide with proper orientations and with sufficient energy to react.
elementary step
An individual step in the mechanism by which a reaction occurs. For each elementary step, the reaction orders do match the reactant coefficients in that step.
enzyme
A protein that acts as a catalyst in a biological system.
fundamental step
See Elementary step.
half-life of a reactant
The time required for half of that reactant to be converted into product(s).
heterogeneous catalyst
A catalyst that exists in a different phase (solid, liquid, or gas) from the reactants; the vast majority of heterogeneous catalysts are solids.
homogeneous catalyst
A catalyst that exists in the same phase (liquid or gas) as the reactants.
integrated rate equation
An equation that relates the concentration of a reactant remaining to the time elapsed; has different mathematical forms for different orders of reaction.
method of initial rates
A method of determining the rate-law expression by carrying out a reaction with different initial concentrations and analyzing the resulting changes in initial rates.
order of a reactant
The power to which the reactant’s concentration is raised in the rate-law expression.
order of a reaction
The sum of the powers to which all concentrations are raised in the rate-law expression; also called the overall order of a reaction.
rate constant
(also called specific rate constant) An experimentally determined proportionality constant that is different for different reactions and that, for a given reaction, changes only with temperature or the presence of a catalyst; k in the rate-law expression, rate = k[A]x[B]y.
rate of reaction
The change in concentration of a reactant or product per unit time.
rate-determining step
The slowest elementary step in a reaction mechanism; the step that limits the overall rate of reaction.
rate-law expression
(also called rate law) An equation that relates the rate of a reaction to the concentrations of the reactants and the specific rate constant; rate = k[A]x[B]y. The exponents of reactant concentrations do not necessarily match the coefficients in the overall balanced chemical equation. The rate-law expression must be determined from experimental data.
reaction coordinate
The progress along the potential energy pathway from reactants to products.
reaction intermediate
A species that is produced and then entirely consumed during a multistep reaction; usually short-lived.
reaction mechanism
The sequence of fundamental steps by which reactants are converted into products.
substrate
A reactant in an enzyme-catalyzed reaction.
thermodynamically favorable (spontaneous) reaction
A reaction that occurs with a net release of free energy, G; a reaction for which ?G is negative.
transition state
A relatively high-energy state in which bonds in reactant molecules are partially broken and new ones are partially formed.
transition state theory
A theory of reaction rates that states that reactants pass through high-energy transition states before forming products.
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