Question 1

For the reaction $$2NO_2(g) + CO(g) ightarrow 2NO(g) + CO_2$(g)$$, the experimentally determined rate law is $$	ext{Rate} = k[NO_2$]^2[CO]^0. $$What is the order of the reaction with respect to CO, and what does this imply about the effect of changing [CO] on the rate?

Accepted Answer

Order is 0; changing [CO] has no effect on the rate.

Question 2

A reaction has the following rate law: $$	ext{Rate} = k[A][B]^2. If $$the concentration of A is doubled and the concentration of B is tripled, by what factor does the reaction rate increase?

Accepted Answer

The rate increases by a factor of 18.

Question 3

Which of the following statements best describes the effect of a catalyst on a chemical reaction?

Accepted Answer

A catalyst provides an alternative pathway with a lower activation energy.

Question 4

For a first-order reaction, $$A ightarrow$$ products, the integrated rate law is $$\ln[A] = -kt + \ln[A]_0. If $$the initial concentration of A is 0.50 M and the rate constant $$k = 0.20\ 	ext{s}^{-1}$$, what is the concentration of A after 10 seconds?

Accepted Answer

$$[A] = 0.067\ 	ext{M}$$

Question 5

Which of the following is true about the half-life of a first-order reaction?

Accepted Answer

It is constant and given by $$t_{1/2} = \frac{0.693}{k}.$$

Question 6

The decomposition of hydrogen peroxide is catalyzed by the enzyme catalase in living organisms. Which statement best explains why this is important for cells?

Accepted Answer

Catalase allows the reaction to proceed at a much faster rate under physiological conditions.

Question 7

For the reaction $$A ightarrow B$$, the following data were collected:

Experiment 1: $$[A]_0 = 0.10\ 	ext{M}$$, initial rate = $$0.020\ 	ext{M/s}$$
Experiment 2: $$[A]_0 = 0.20\ 	ext{M}$$, initial rate = $$0.040\ 	ext{M/s}$$

What is the order of the reaction with respect to A?

Accepted Answer

First order

Question 8

A certain reaction has an activation energy of $$75\ 	ext{kJ/mol}. $$According to the Arrhenius equation, what will happen to the rate constant $$k if $$the temperature is increased?

Accepted Answer

The rate constant $$k$$ will increase.

Question 9

Which of the following best describes a reaction intermediate?

Accepted Answer

A substance that is formed in one step of a mechanism and consumed in a subsequent step.

Question 10

For the reaction $$2A ightarrow B$$, the rate law is $$	ext{Rate} = k[A]^2. If $$the initial concentration of A is $$0.50\ 	ext{M}$$ and the rate constant $$k = 0.10\ 	ext{M}^{-1}	ext{s}^{-1}$$, what is the half-life of A?

Accepted Answer

$$t_{1/2} = \frac{1}{k[A]_0}$$

Question 11

A student is monitoring the reaction $$A \rightarrow$$ products and plots $$[A]$$ versus time, $$\ln[A]$$ versus time, and $$1/[A]$$ versus time. Only the $$1/[A]$$ versus time plot is linear. What is the order of the reaction?

Accepted Answer

Second order

Question 12

Which of the following is NOT a requirement for a successful collision according to collision theory?

Accepted Answer

Reactant molecules must be in the gas phase.

Question 13

The rate law for a reaction is found to be $$	ext{Rate} = k[NO_2$]^2. $$Which of the following mechanisms is consistent with this rate law?

Accepted Answer

A mechanism in which the slow step involves two $$NO_2$$ molecules colliding.

Question 14

A reaction is found to be zero order in reactant A. Which of the following statements is true?

Accepted Answer

The rate of reaction is independent of [A].

Question 15

In a catalytic converter in a car, which of the following best describes the role of the catalyst?

Accepted Answer

It provides a surface for the reaction to occur, lowering the activation energy.

Question 16

The Arrhenius equation is $$k = Ae$$^{-E_a/(RT)}$$. Which of the following changes will increase the value of the rate constant k$?

Accepted Answer

Increasing the temperature.

Question 17

Which of the following is a correct statement about the rate-determining step in a reaction mechanism?

Accepted Answer

It determines the overall rate law for the reaction.

Question 18

A reaction has a rate law $$	ext{Rate} = k[A][B]. If $$the initial concentrations are $$[A]_0 = 0.10\ 	ext{M}$$ and $$[B]_0 = 0.20\ 	ext{M}$$, and the rate constant $$k = 0.50\ 	ext{M}^{-1}	ext{s}^{-1}$$, what is the initial rate?

Accepted Answer

$$0.005\ 	ext{M/s}$$

Question 19

Which of the following best explains why most reaction mechanisms do not involve termolecular elementary steps?

Accepted Answer

The probability of three molecules colliding simultaneously with proper orientation is extremely low.

Chemical Kinetics: Rates of Chemical Reactions

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