Chapter 13

Question 1

chemical kinetics

Answer 1

is the study of reaction rates, including how reaction rates change with varying conditions and which molecular events occur during the overall reaction.

Question 2

Factors Affecting Rate of Reaction

Answer 2

1. Concentrations of reactants
2. Concentration of catalyst
3. Temperature at which reaction occurs
4. Surface area of a solid reactant or catalyst

Question 3

Reaction rate

Answer 3

is the increase in molar concentration of product of a reaction per unit time or the decrease in molar concentration of reactant per unit time. The unit is usually mol/(L • s) or M/s

Question 4

reaction rate equations give

Answer 4

the average rate over the time interval t.

Question 5

As t decreases and approaches zero,

Answer 5

the equations give the instantaneous rate.

Question 6

Rates are determined experimentally in a variety of ways. For example

Answer 6

samples can be taken and analyzed from the reaction at several different intervals. Continuously following the reaction is more convenient. This can be done by measuring pressure, as shown on the next slide, or by measuring light absorbance when a color change is part of the reaction

Question 7

The reaction rate usually depends on

Answer 7

the concentration of one or more reactant. This relationship must be determined by experiment

Question 8

the rate law,

Answer 8

an equation that relates the rate of a reaction to the concentration of a reactant (and catalyst) raised to various powers. The proportionality constant, k, is the rate constant.

Question 9

reaction order with respect to a specific reactant is the

Answer 9

exponent of that species in the experimentally determined rate law.

Question 10

The overall order of a reaction is the

Answer 10

sum of the orders of the reactant species from the experimentally determined rate law.

Question 11

The rate law tells us the relationship between

Answer 11

the rate and the concentrations of reactants and catalysts.

Question 12

To find concentrations at various times, we need to use the

Answer 12

ntegrated rate law. The form used depends on the order of reaction in that reactant.

Question 13

The half-life of a reaction, t½, is the

Answer 13

time it takes for the reactant concentration to decrease to one-half of its initial value.

Question 14

the rate law is in the form of

Answer 14

y = mx + b, allowing us to use the slope and intercept to find the values

Question 15

__________ can also be used to determine the order of reaction in that reactant.

Answer 15

Graphs of concentration and time

Question 16

The rate constant depends strongly on

Answer 16

temperature

Question 17

Collision theory

Answer 17

assumes that reactant molecules must collide with an energy greater than some minimum value and with the proper orientation

Question 18

The minimum energy is called the

Answer 18

activation energy

Question 19

Transition-state theory

Answer 19

explains the reaction resulting from the collision of two molecules in terms of an activated complex (transition state)

Question 20

activated complex (transition state)

Answer 20

an unstable grouping of atoms that can break up to form products.

Question 21

The potential energy diagram for a reaction visually illustrates the

Answer 21

changes in energy that occur

Question 22

the reaction may take place in several steps. That set of steps is called the

Answer 22

reaction mechanism

Question 23

Each step in the reaction mechanism is called an

Answer 23

elementary reaction

Question 24

the rate of an elementary reaction is proportional to the

Answer 24

concentration of each reactant molecule.

Question 25

The slowest step in the reaction mechanism is called the

Answer 25

rate-determining step (RDS). The rate law for the RDS is the rate law for the overall reaction.

Question 26

The rate of a reaction is determined completely by

Answer 26

the slowest step, the rate-determining step.

Question 27

reaction intermediate

Answer 27

a species produced during a reaction that does not appear in the net equation because it reacts in a subsequent step in the mechanism.

Question 28

Catalysis is an

Answer 28

increase in the rate of reaction that results from the addition of a catalyst.

Question 29

A catalyst is not

Answer 29

consumed in a reaction. Rather, it is present in the beginning, is used in one step, and is produced again in a subsequent step. As a result, the catalyst does not appear in the overall reaction equation.

Question 30

A catalyst increases the reaction rate by

Answer 30

providing an alternative reaction path with a lower activation energy. When Ea is reduced, k increases exponentially.