Question 1

Which of the following best explains why lizards become lethargic at low temperatures, based on chemical kinetics?

Accepted Answer

Low temperatures decrease the frequency of effective collisions between reactant molecules in their bodies.

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:

| [NO$$_2$$] (M) | [CO] (M) | Initial Rate (M/s) |
|---|---|---|
| 0.10 | 0.10 | 0.0021 |
| 0.20 | 0.10 | 0.0082 |
| 0.20 | 0.20 | 0.0083 |
| 0.40 | 0.10 | 0.033 |

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

Accepted Answer

Second order

Question 3

Which of the following changes will increase the rate of a reaction according to the collision model?

Accepted Answer

Increasing the surface area of a solid reactant

Question 4

A reaction is found to be first order in A. Which of the following graphs will yield a straight line?

Accepted Answer

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

Question 5

The half-life of a first-order reaction is 26.4 seconds. How long will it take for the concentration of the reactant to fall to one-eighth of its initial value?

Accepted Answer

79.2 seconds

Question 6

Which of the following statements about the Arrhenius equation is correct?

Accepted Answer

The rate constant $$k$$ increases as temperature increases.

Question 7

Given the Arrhenius equation $$k = Ae$$^{-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 8

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

Accepted Answer

4

Question 9

Which of the following best describes the role of a catalyst in a chemical reaction?

Accepted Answer

It provides an alternative pathway with a lower activation energy.

Question 10

For a reaction with the integrated rate law $$\frac{1}{[A]_t} = kt + \frac{1}{[A]_0}$$, what is the order of the reaction?

Accepted Answer

Second order

Question 11

Which experimental technique would be most appropriate for continuously monitoring the concentration of a colored reactant during a fast reaction?

Accepted Answer

Spectroscopy

Question 12

In a reaction mechanism, what is an intermediate?

Accepted Answer

A species that is produced in one step and consumed in a later step

Question 13

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

Accepted Answer

The rate is constant over time.

Question 14

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

Accepted Answer

$$0.0050\ 	ext{M/s}$$

Question 15

Which of the following is a criterion for validating a proposed reaction mechanism?

Accepted Answer

The sum of the elementary steps must equal the overall balanced equation.

Question 16

Which of the following statements about enzymes is correct?

Accepted Answer

Enzymes lower the activation energy of biological reactions.

Question 17

If a reaction is second order, how does the half-life change as the initial concentration increases?

Accepted Answer

The half-life decreases.

Question 18

Which of the following best describes the rate-determining step in a reaction mechanism?

Accepted Answer

It determines the overall rate law for the reaction.

Question 19

A reaction has an activation energy of $$50\ 	ext{kJ/mol}. If $$the temperature is increased, what happens to the fraction of molecules with enough energy to react?

Accepted Answer

It increases.

Question 20

Which of the following is true about the molecularity of an elementary step?

Accepted Answer

It is the number of reactant particles involved in the step.

Chemical Kinetics: Factors Affecting Reaction Rates and Mechanisms

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