kinetics

Question 1

activated complex

Answer 1

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

Question 2

activation energy (Ea)

Answer 2

minimum energy necessary in order for a reaction to take place

Question 3

Arrhenius equation

Answer 3

the mathematical relationship between a reaction’s rate constant, activation energy, and temperature

Question 4

average rate

Answer 4

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

Question 5

bimolecular reaction

Answer 5

elementary reaction involving two reactant species

Question 6

catalyst

Answer 6

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

Question 7

collision theory

Answer 7

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

Question 8

elementary reaction

Answer 8

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

Question 9

frequency factor (A)

Answer 9

proportionality constant in the Arrhenius equation, related to the relative number of collisions having an orientation capable of leading to product formation

Question 10

half-life of a reaction (tl/2)

Answer 10

time required for half of a given amount of reactant to be consumed

Question 11

heterogeneous catalyst

Answer 11

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

Question 12

homogeneous catalyst

Answer 12

catalyst present in the same phase as the reactants

Question 13

initial rate

Answer 13

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

Question 14

instantaneous rate

Answer 14

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

Question 15

integrated rate law

Answer 15

equation that relates the concentration of a reactant to elapsed time of reaction

Question 16

intermediate

Answer 16

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

Question 17

method of initial rates

Answer 17

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

Question 18

molecularity

Answer 18

number of reactant species involved in an elementary reaction

Question 19

overall reaction order

Answer 19

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

Question 20

rate constant (k)

Answer 20

proportionality constant in a rate law

Question 21

rate expression

Answer 21

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

Question 22

rate law

Answer 22

(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

Question 23

rate of reaction

Answer 23

measure of the speed at which a chemical reaction takes place

Question 24

rate-determining step

Answer 24

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

Question 25

reaction diagram

Answer 25

used in chemical kinetics to illustrate various properties of a reaction

Question 26

reaction mechanism

Answer 26

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

Question 27

reaction order

Answer 27

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)

Question 28

termolecular reaction

Answer 28

elementary reaction involving three reactant species

Question 29

unimolecular reaction

Answer 29

elementary reaction involving a single reactant species