Question 1

Which of the following best explains why lizards become lethargic when their body temperature drops, in terms of chemical kinetics?

Accepted Answer

Lower temperatures decrease the kinetic energy of molecules, resulting in fewer collisions with enough energy to overcome the activation barrier.

Question 2

For the reaction $$2	ext{NO}_2(g) + 2	ext{CO}(g) ightarrow 2	ext{CO}_2(g) + 	ext{N}_2(g)$$, the following initial rates were measured:

Experiment 1: $$[	ext{NO}_2] = 0.10 M$$, $$[	ext{CO}] = 0.10 M$$, Rate = $$0.0021 M/s
$$Experiment 2: $$[	ext{NO}_2] = 0.20 M$$, $$[	ext{CO}] = 0.10 M$$, Rate = $$0.0082 M/s

$$What is the order of the reaction with respect to $$	ext{NO}_2$$?

Accepted Answer

Second order

Question 3

Which of the following rate laws corresponds to a reaction that is first order with respect to $$A$$ and zero order with respect to $$B$$?

Accepted Answer

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

Question 4

A reaction is found to be second order overall. If the initial concentration of reactant $$A is $$doubled, what happens to the initial rate of the reaction?

Accepted Answer

The rate quadruples.

Question 5

Which of the following graphs would be linear for a first-order reaction?

Accepted Answer

$$\ln[A] vs. $$time

Question 6

The half-life of a first-order reaction is given by which of the following equations?

Accepted Answer

$$t_{1/2} = \frac{0.693}{k}$$

Question 7

A reaction has a rate law $$	ext{Rate} = k[A]^2. If $$the initial concentration of $$A is$$ $$0.100 M $$and the initial rate is $$0.0100 M/s$$, what is the rate when $$[A] = 0.500 M$$?

Accepted Answer

$$0.250 M/s$$

Question 8

Which of the following statements best explains why reaction rates generally increase with increasing temperature?

Accepted Answer

A greater fraction of molecules has enough thermal energy to surmount the activation barrier.

Question 9

The Arrhenius equation is $$k = Ae$$^{-E_a/(RT)}$$. What does the exponential factor e$$^{-E_a/(RT)}$$ represent?

Accepted Answer

The fraction of molecules with enough energy to overcome the activation barrier.

Question 10

Which of the following is true for a zero-order reaction?

Accepted Answer

The rate is independent of the concentration of the reactant.

Question 11

A catalyst increases the rate of a chemical reaction by:

Accepted Answer

Providing an alternative pathway with a lower activation energy.

Question 12

Which of the following statements about reaction mechanisms is correct?

Accepted Answer

The rate law for an elementary step can be written directly from its molecularity.

Question 13

For a reaction with the following mechanism:
Step 1 (slow): $$A + B \rightarrow C$$
Step 2 (fast): $$C + D \rightarrow E$$
What is the rate law for the overall reaction?

Accepted Answer

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

Question 14

Which of the following best describes the effect of a heterogeneous catalyst in a reaction?

Accepted Answer

It provides a surface that orients reactant molecules for effective collisions.

Question 15

A first-order reaction has a half-life of 20 minutes. If the initial concentration is $$0.80 M$$, what will the concentration be after 60 minutes?

Accepted Answer

$$0.20 M$$

Question 16

Which of the following is NOT a method for continuously monitoring the progress of a chemical reaction?

Accepted Answer

Titration

Question 17

Which of the following statements about the collision model is correct?

Accepted Answer

Only collisions with sufficient energy and proper orientation result in a reaction.

Question 18

Which of the following best describes an intermediate in a reaction mechanism?

Accepted Answer

A substance that is produced in one step and consumed in a later step of the mechanism.

Question 19

Which of the following is true for a second-order reaction with respect to $$A$$?

Accepted Answer

A plot of $$1/[A] vs. $$time is linear.

Chemical Kinetics: Rates, Mechanisms, and Catalysis

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