Q: For the reaction $$2\,\mathrm{NO}_2(g) \rightarrow 2\,\mathrm{NO}(g) + \mathrm{O}_2(g)$$, which of the following correctly expresses the rate of disappearance of $$\mathrm{NO}_2 in $$terms of the rate of appearance of $$\mathrm{O}_2$$?

$$\text{Rate} = -\dfrac{1}{2} \dfrac{d[\mathrm{NO}_2]}{dt} = \dfrac{d[\mathrm{O}_2]}{dt}$$

Q: A reaction has a rate constant $$k_1 = 2.5$$ \times $$10^{-3}$$\,\mathrm{s}^{-1}$$ at 300$$\,\mathrm{K}$$ and k_2$ = 7.5 \times 10$$^{-3}$$\,\mathrm{s}^{-1} at$$ $$320\,\mathrm{K}. $$Using the two-point form of the Arrhenius equation, what is the activation energy $$E_a$$? ($$R = 8.314\,\mathrm{J\,$$mol^{-1}$$\,K$$^{-1}$$})$$

$$E_a = \dfrac{8.314 \times \ln(7.5 \times 10$$^{-3}$$ / 2.5 \times 10$$^{-3}$$)}{(1/300) - (1/320)} = 4.0 \times 10$$^{4}$$\,\mathrm{J\,$$mol^{-1}$$}$$

Question 1

Which of the following best defines chemical kinetics?

Accepted Answer

The study of the rates at which chemical processes occur and the factors that affect these rates.

Question 2

For the reaction $$2\,\mathrm{NO}_2(g) \rightarrow 2\,\mathrm{NO}(g) + \mathrm{O}_2(g)$$, which of the following correctly expresses the rate of disappearance of $$\mathrm{NO}_2 in $$terms of the rate of appearance of $$\mathrm{O}_2$$?

Accepted Answer

$$	ext{Rate} = -\dfrac{1}{2} \dfrac{d[\mathrm{NO}_2]}{dt} = \dfrac{d[\mathrm{O}_2]}{dt}$$

Question 3

A reaction is found to be first order in $$A$$ and second order in $$B. $$Which of the following is the correct rate law for this reaction?

Accepted Answer

$$	ext{Rate} = k[A][B]^2$$

Question 4

Which statement correctly describes the effect of reactant concentration on the rate of a zero-order reaction?

Accepted Answer

The rate is independent of the reactant concentration.

Question 5

Given the following initial rate data for the reaction $$A + B \rightarrow C$$:

- Experiment 1: $$[A]=0.10\,\mathrm{M}$$, $$[B]=0.10\,\mathrm{M}$$, Rate = $$0.020\,\mathrm{M/s}
- $$Experiment 2: $$[A]=0.20\,\mathrm{M}$$, $$[B]=0.10\,\mathrm{M}$$, Rate = $$0.040\,\mathrm{M/s}
- $$Experiment 3: $$[A]=0.10\,\mathrm{M}$$, $$[B]=0.20\,\mathrm{M}$$, Rate = $$0.080\,\mathrm{M/s}$$

What is the rate law for this reaction?

Accepted Answer

$$	ext{Rate} = k[A][B]^2$$

Question 6

For a first-order reaction, which of the following is the correct integrated rate law?

Accepted Answer

$$\ln [A]_t = -kt + \ln [A]_0$$

Question 7

The units of the rate constant $$k$$ for a second-order reaction are:

Accepted Answer

$$\mathrm{M}^{-1}\,\mathrm{s}^{-1}$$

Question 8

A reaction has a half-life of 10 minutes and follows first-order kinetics. What is the rate constant $$k$$ for this reaction?

Accepted Answer

$$k = \dfrac{0.693}{10\,\mathrm{min}} = 0.0693\,\mathrm{min}^{-1}$$

Question 9

Which graphical plot would yield a straight line for a second-order reaction with respect to $$A$$?

Accepted Answer

$$\dfrac{1}{[A]} vs$$. $$t$$

Question 10

The Arrhenius equation is $$k = A e$$^{-E_a/(RT)}$$. Which term represents the activation energy?

Accepted Answer

$$E_a$$

Question 11

A reaction has a rate constant $$k_1 = 2.5$$ 	imes $$10^{-3}$$\,\mathrm{s}^{-1}$$ at 300$$\,\mathrm{K}$$ and k_2$ = 7.5 	imes 10$$^{-3}$$\,\mathrm{s}^{-1} at$$ $$320\,\mathrm{K}. $$Using the two-point form of the Arrhenius equation, what is the activation energy $$E_a$$? ($$R = 8.314\,\mathrm{J\,$$mol^{-1}$$\,K$$^{-1}$$})$$

Accepted Answer

$$E_a = \dfrac{8.314 	imes \ln(7.5 	imes 10$$^{-3}$$ / 2.5 	imes 10$$^{-3}$$)}{(1/300) - (1/320)} = 4.0 	imes 10$$^{4}$$\,\mathrm{J\,$$mol^{-1}$$}$$

Question 12

On a potential energy diagram for a chemical reaction, what does the difference in energy between the reactants and products represent?

Accepted Answer

The overall energy change ($$\Delta E) of $$the reaction.

Question 13

According to collision theory, which of the following is NOT required for a successful reaction between two molecules?

Accepted Answer

The molecules must be in the same phase.

Question 14

Which of the following statements about catalysts is correct?

Accepted Answer

A catalyst increases the rate of a reaction by lowering the activation energy.

Question 15

A reaction mechanism consists of the following steps:

1) $$A + B \rightarrow C ($$slow)
2) $$C + D \rightarrow E ($$fast)

What is the rate law for the overall reaction?

Accepted Answer

$$	ext{Rate} = k[A][B]$$

Question 16

Which of the following best describes a reaction intermediate?

Accepted Answer

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

Question 17

Which of the following is an example of heterogeneous catalysis?

Accepted Answer

The catalytic converter in a car, where solid platinum catalyzes gas-phase reactions.

Question 18

If the half-life of a reactant in a first-order reaction is 5.0 minutes, how long will it take for the concentration to decrease to one-eighth of its original value?

Accepted Answer

15.0 minutes

Question 19

Which of the following statements is true regarding the rate-determining step in a reaction mechanism?

Accepted Answer

It is the slowest step in the mechanism and determines the overall reaction rate.

Question 20

A certain reaction is found to be zero order in $$A. If $$the initial concentration of $$A is$$ $$0.50\,\mathrm{M}$$ and the rate constant $$k is$$ $$0.10\,\mathrm{M\,s$$^{-1}$$}$$, how long will it take for $$A to $$decrease to $$0.20\,\mathrm{M}$$?

Accepted Answer

$$t = \dfrac{[A]_0 - [A]_t}{k} = \dfrac{0.50 - 0.20}{0.10} = 3.0\,\mathrm{s}$$

Chemical Kinetics: Study Guide and Key Concepts (CHE 111, Chapter 15)

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