Chapter 16

Question 1

activation energy

Answer 1

the minimum energy with which molecules must collide to react

Question 2

active site

Answer 2

the region of an enzyme formed by specific amino-acid side chains at which catalysis occurs

Question 3

Arrhenius equation

Answer 3

an equation that expresses the exponential relationship between temperature and the rate constant: k = Ae^-Ea/RT

Question 4

average rate

Answer 4

the change in concentration of reactants (or products) divided by a finite time period

Question 5

biomolecular reaction

Answer 5

an elementary reaction involving the collision of two reactant species

Question 6

catalyst

Answer 6

a substance or mixture that increases the rate of a reaction without being used up in the process

Question 7

chemical kinetics

Answer 7

the study of the rates of reactions and the factors that affect them

Question 8

collision theory

Answer 8

a model that explains reaction rate as based on the number, energy, and orientation of colliding particles

Question 9

effective collision

Answer 9

a collision in which the particles meet with sufficient energy and an orientation that allows them to react

Question 10

elementary reaction (elementary step)

Answer 10

a simple reaction that describes a single molecular event in a proposed reaction mechanism

Question 11

enzyme

Answer 11

a biological macromolecule (usually a protein) that acts as a catalyst

Question 12

enzyme substrate complex

Answer 12

the intermediate in an enzyme-catalyzed reaction, which consists of enzyme and substrate(s) and whose concentration determines the rate of product formation

Question 13

frequency factor

Answer 13

the product of the collision frequency Z and an orientation probability factor p that is specific for a reaction

Question 14

half-life

Answer 14

in chemical processes, the time required for the reactant concentration to reach half of its initial value. In nuclear processes, the time required for half the initial number of nuclei in a sample to decay

Question 15

heterogeneous catalyst

Answer 15

a catalyst that occurs in a different phase from the reactants, usually a solid interacting with gaseous or liquid reactants

Question 16

homogeneous catalyst

Answer 16

a catalyst (gas, liquid, or soluble solid) that exists in the same phase as the reactants

Question 17

hydrogenation

Answer 17

the addition of hydrogen to a carbon-carbon multiple bond to form a carbon-carbon single bond

Question 18

induced fit model

Answer 18

a model of enzyme action that pictures the binding of the substrate as inducing the active site to change its shape and become catalytically active

Question 19

initial rate

Answer 19

the instantaneous rate at the moment the reactants are mixed, that is, at t = 0

Question 20

instantaneous rate

Answer 20

the reaction rate at a particular time, given by the slope of a tangent to a plot of reactant concentration vs. time

Question 21

integrated rate law

Answer 21

a mathematical expression for reactant concentration as a function of time

Question 22

lock and key model

Answer 22

a model of enzyme function that pictures the enzyme active site and the substrate as rigid shapes that fit together as a lock and key, respectively

Question 23

molecularity

Answer 23

the number of reactant particles involved in an elementary step

Question 24

rate constant (k)

Answer 24

the proportionality constant that relates reaction rate to reactant (and product) concentrations

Question 25

rate-determining (rate-limiting) step

Answer 25

the slowest step in a reaction mechanism and therefore the step that limits the overall rate

Question 26

rate law (rate equation)

Answer 26

an equation that expresses the rate of a reaction as a function of reactant (and product) concentrations and temperature

Question 27

reaction energy diagram

Answer 27

a graph that shows the potential energy of a reacting system as it progresses from reactants to products

Question 28

reaction intermediate

Answer 28

a substance that is formed and used up during the overall reaction and therefore does not appear in the overall equation

Question 29

reaction mechanism

Answer 29

a series of elementary steps that sum to the overall reaction and is consistent with the rate law

Question 30

reaction orders

Answer 30

the exponent of a reactant concentration in a rate law that shows how the rate is affected by changes in that concentration

Question 31

reaction rate

Answer 31

the change in the concentrations of reactants (or products) with time

Question 32

substrate

Answer 32

a reactant that binds to the active site in an enzyme-catalyzed reaction

Question 33

transition state (activated complex)

Answer 33

an unstable species formed in an effective collision of reactants that exists momentarily when the system is highest in energy and that can either form products or re-form reactants

Question 34

transition state theory

Answer 34

a model that explains how the energy of reactant collisions is used to form a high-energy transitional species that can change to reactant or product

Question 35

unimolecular reaction

Answer 35

an elementary reaction that involves the decomposition or rearrangement of a single particle