Book: Key Terms: 16

Question 1

activation energy (E_a)

Answer 1

an energy threshold that the colliding molecules must exceed in order to react

Question 2

active site

Answer 2

a small part of an enzyme’s surface, a region whose shape results from the amino-acid side chains involved in catalyzing the reaction

Question 3

Arrhenius equation

Answer 3

k = A e^(-E_a / (RT)), where k is the rate constant, T is the absolute temperature, R is the universal gas constant, E_a is the activation energy

Question 4

average rate

Answer 4

over a given period of time, the average rate is the slope of the line joining two points along the curve

Question 5

bimolecular reaction

Answer 5

a reaction in which two particles collide and react

Question 6

catalyst

Answer 6

a substance that increases the reaction rate without being consumed

Question 7

chemical kinetics

Answer 7

the study of how fast reactants change into products throughout the course of a chemical reaction

Question 8

collision theory

Answer 8

atoms, molecules, ions, must collide to react in this model

Question 9

effective collision

Answer 9

the collisions that actually lead to product because the atoms that become bonded in the product make contact

Question 10

elementary reaction (elementary setup)

Answer 10

the individual steps that make up a reaction mechanism. Each describes a single molecular event—one particle decomposing, two particles combining, etc.

Question 11

enzyme

Answer 11

a protein catalyst

Question 12

enzyme-substrate complex

Answer 12

substrate and enzyme form an intermediate enzyme-substrate complex (ES), whose concentration determines the rate of formation of product.

Question 13

frequency factor

Answer 13

the term A in the Arrhenius equation, which gives molecular orientation: it is given by A = pZ, where p is the orientation probability factor and Z is the collision frequency.

Question 14

half-life (t_1/2)

Answer 14

the time it takes for reactant concentration to reach half its initial value in a reaction.

Question 15

heterogeneous catalyst

Answer 15

speeds up a reaction in a different phase, such as solids interacting with gas or liquid reactants.

Question 16

homogeneous catalyst

Answer 16

catalyst that is both in the same phase as the reactants and products and exists in a solution with the reaction mixture.

Question 17

hydrogenation

Answer 17

An example of a heterogeneous catalyst which reduces carbon-carbon double bonds to single bonds by the introduction of H2

Question 18

induced-fit model

Answer 18

In this model, the substrate in enzyme action induces the active site to adopt a perfect fit; the enzyme changes shape when the substrate lands at the active site.

Question 19

initial rate

Answer 19

The instantaneous rate at the moment the reactants are mixed (t=0).

Question 20

instantaneous rate

Answer 20

The rate at a particular instant during the reaction.

Question 21

integrated rate laws

Answer 21

Forms of the rate equation that include time as a variable as to answer questions about how long it takes a specific process to occur.

Question 22

lock-and-key model

Answer 22

An older model which suggests enzyme action is characterized by a “key” (substrate) fitting a “lock” (active site), and then the chemical change proceeds.

Question 23

molecularity

Answer 23

Characterizes an elementary step; equal to the number of reactant particles in the step.

Question 24

rate constant

Answer 24

A proportionality constant showing up in the rate law that is specific for a given reaction at a given temperature.

Question 25

rate-determining (rate-limiting) step

Answer 25

One step in a set of elementary steps is usually much slower than all of the others. This is the rate-determining step (or rate-limiting step), as it limits how fast the overall reaction proceeds.

Question 26

rate law (rate law)

Answer 26

Expresses the rate of reaction as a function of concentrations and temperatures: Rate = k [A]^m [B]^n …

Question 27

reaction energy diagram

Answer 27

Plots how potential energy changes as the reaction proceeds from reactants to products (the reaction progress).

Question 28

reaction intermediate

Answer 28

A substance formed in one step of the mechanism of a reaction and used up in a subsequent step during the reaction.

Question 29

reaction mechanism

Answer 29

A sequence of single reaction steps that sum to the overall equation for a reaction.

Question 30

reaction orders

Answer 30

The exponents m and n in the rate law: r = k [A]^m [B]^n, which generally define how the rate is affected by reactant concentration.

Question 31

reaction rate

Answer 31

The change in the concentrations of reactants or products as a function of time.

Question 32

substrate

Answer 32

Reactant molecules in biological reactions involving active sites.

Question 33

transition state (activated complex)

Answer 33

In the transition state theory, at some point during a reaction an unstable species neither reactant nor product arises with partial bonds at the instant of highest potential energy. The activation energy of a reaction is used to reach the transition state.

Question 34

transition state theory

Answer 34

A model that focuses on the high-energy species that exists at the moment of an effective collision when reactants are becoming products.

Question 35

unimolecular reaction

Answer 35

An elementary step that involves the decomposition or rearrangement of a single particle.