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8.9: Key Terms

Last updated

Aug 23, 2023
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- 8.8: Catalysis
- 8.10: Key Equations

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Example and Directions
Words (or words that have the same definition)	The definition is case sensitive	(Optional) Image to display with the definition [Not displayed in Glossary, only in pop-up on pages]	(Optional) Caption for Image	(Optional) External or Internal Link	(Optional) Source for Definition
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Glossary Entries
Word(s)	Definition	Image	Caption	Link	Source
activated complex	(also, transition state) unstable combination of reactant species formed during a chemical reaction
activation energy (E_a)	minimum energy necessary in order for a reaction to take place
Arrhenius equation	mathematical relationship between a reaction’s rate constant, activation energy, and temperature
average rate	rate of a chemical reaction computed as the ratio of a measured change in amount or concentration of substance to the time interval over which the change occurred
bimolecular reaction	elementary reaction involving two reactant species
catalyst	substance that increases the rate of a reaction without itself being consumed by the reaction
collision theory	model that emphasizes the energy and orientation of molecular collisions to explain and predict reaction kinetics
elementary reaction	reaction that takes place in a single step, precisely as depicted in its chemical equation
frequency factor (A)	proportionality constant in the Arrhenius equation, related to the relative number of collisions having an orientation capable of leading to product formation
half-life of a reaction (t_l/2)	time required for half of a given amount of reactant to be consumed
heterogeneous catalyst	catalyst present in a different phase from the reactants, furnishing a surface at which a reaction can occur
homogeneous catalyst	catalyst present in the same phase as the reactants
initial rate	instantaneous rate of a chemical reaction at t = 0 s (immediately after the reaction has begun)
instantaneous rate	rate of a chemical reaction at any instant in time, determined by the slope of the line tangential to a graph of concentration as a function of time
integrated rate law	equation that relates the concentration of a reactant to elapsed time of reaction
intermediate	species produced in one step of a reaction mechanism and consumed in a subsequent step
method of initial rates	common experimental approach to determining rate laws that involves measuring reaction rates at varying initial reactant concentrations
molecularity	number of reactant species involved in an elementary reaction
overall reaction order	sum of the reaction orders for each substance represented in the rate law
rate constant (k)	proportionality constant in a rate law
rate expression	mathematical representation defining reaction rate as change in amount, concentration, or pressure of reactant or product species per unit time
rate law	(also, rate equation) (also, differential rate laws) mathematical equation showing the dependence of reaction rate on the rate constant and the concentration of one or more reactants
rate of reaction	measure of the speed at which a chemical reaction takes place
rate-determining step	(also, rate-limiting step) slowest elementary reaction in a reaction mechanism; determines the rate of the overall reaction
reaction diagram	used in chemical kinetics to illustrate various properties of a reaction
reaction mechanism	stepwise sequence of elementary reactions by which a chemical change takes place
reaction order	value of an exponent in a rate law (for example, zero order for 0, first order for 1, second order for 2, and so on)
termolecular reaction	elementary reaction involving three reactant species
unimolecular reaction	elementary reaction involving a single reactant species

activated complex | (also, transition state) unstable combination of reactant species formed during a chemical reaction

activation energy (E_a) | minimum energy necessary in order for a reaction to take place

Arrhenius equation | mathematical relationship between a reaction’s rate constant, activation energy, and temperature

average rate | rate of a chemical reaction computed as the ratio of a measured change in amount or concentration of substance to the time interval over which the change occurred

bimolecular reaction | elementary reaction involving two reactant species

catalyst | substance that increases the rate of a reaction without itself being consumed by the reaction

collision theory | model that emphasizes the energy and orientation of molecular collisions to explain and predict reaction kinetics

elementary reaction | reaction that takes place in a single step, precisely as depicted in its chemical equation

frequency factor (A) | proportionality constant in the Arrhenius equation, related to the relative number of collisions having an orientation capable of leading to product formation

half-life of a reaction (t_l/2) | time required for half of a given amount of reactant to be consumed

heterogeneous catalyst | catalyst present in a different phase from the reactants, furnishing a surface at which a reaction can occur

homogeneous catalyst | catalyst present in the same phase as the reactants

initial rate | instantaneous rate of a chemical reaction at t = 0 s (immediately after the reaction has begun)

instantaneous rate | rate of a chemical reaction at any instant in time, determined by the slope of the line tangential to a graph of concentration as a function of time

integrated rate law | equation that relates the concentration of a reactant to elapsed time of reaction

intermediate | species produced in one step of a reaction mechanism and consumed in a subsequent step

method of initial rates | common experimental approach to determining rate laws that involves measuring reaction rates at varying initial reactant concentrations

molecularity | number of reactant species involved in an elementary reaction

overall reaction order | sum of the reaction orders for each substance represented in the rate law

rate constant (k) | proportionality constant in a rate law

rate expression | mathematical representation defining reaction rate as change in amount, concentration, or pressure of reactant or product species per unit time

rate law | (also, rate equation) (also, differential rate laws) mathematical equation showing the dependence of reaction rate on the rate constant and the concentration of one or more reactants

rate of reaction | measure of the speed at which a chemical reaction takes place

rate-determining step | (also, rate-limiting step) slowest elementary reaction in a reaction mechanism; determines the rate of the overall reaction

reaction diagram | used in chemical kinetics to illustrate various properties of a reaction

reaction mechanism | stepwise sequence of elementary reactions by which a chemical change takes place

reaction order | value of an exponent in a rate law (for example, zero order for 0, first order for 1, second order for 2, and so on)

termolecular reaction | elementary reaction involving three reactant species

unimolecular reaction | elementary reaction involving a single reactant species

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