Question 1

Which of the following statements best explains why the conversion of diamond to graphite is considered spontaneous but is not observed in a human lifetime?

Accepted Answer

The reaction has a high activation energy, making the rate extremely slow.

Question 2

A reaction is found to proceed much faster when the reactants are in aqueous solution compared to when they are both solids. Which factor is primarily responsible for this difference?

Accepted Answer

Surface area of reactants

Question 3

For the reaction $$2NO_2(g) \rightarrow O_2$(g) + 2NO(g)$$, which of the following correctly relates the rates of change in concentration?

Accepted Answer

$$-\frac{1}{2} \frac{\Delta[NO_2$]}{\Delta t} = \frac{1}{2} \frac{\Delta[NO]}{\Delta t} = \frac{\Delta[O_2$]}{\Delta t}$$

Question 4

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

Accepted Answer

It lowers the activation energy, increasing the rate of both the forward and reverse reactions.

Question 5

Given the rate law $$	ext{Rate} = k[A]^2[B]$$, what is the overall order of the reaction?

Accepted Answer

Third order

Question 6

A reaction has a rate law $$	ext{Rate} = k[A]^0[B]^1. If $$the concentration of $$[A] is $$doubled and $$[B] is $$tripled, how does the rate change?

Accepted Answer

The rate is tripled.

Question 7

Which graphical method would yield a straight line for a first-order reaction?

Accepted Answer

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

Question 8

The half-life for a first-order reaction is given by which equation?

Accepted Answer

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

Question 9

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

Accepted Answer

It is the slowest step and limits the overall reaction rate.

Question 10

The Arrhenius equation relates the rate constant $$k to $$temperature $$T$$ and activation energy $$E_a. $$Which form of the equation allows you to determine $$E_a$$ from a plot?

Accepted Answer

$$\ln k = -\frac{E_a}{R}\frac{1}{T} + \ln A$$

Question 11

Which of the following best describes a heterogeneous catalyst?

Accepted Answer

A catalyst in a different phase than the reactants, often providing a surface for the reaction.

Question 12

In the hydrogenation of ethylene using a nickel catalyst, which step involves the actual chemical transformation?

Accepted Answer

Reaction of the adsorbed substances on the catalyst surface

Question 13

Which of the following is NOT a requirement for a proposed reaction mechanism to be valid?

Accepted Answer

Each elementary step must be bimolecular.

Question 14

A reaction is found to be second order overall. Which of the following integrated rate laws describes the concentration of reactant $$A$$ over time?

Accepted Answer

$$\frac{1}{[A]} = kt + \frac{1}{[A]_0}$$

Question 15

Which of the following best explains why increasing temperature generally increases the rate of a chemical reaction?

Accepted Answer

More molecules have sufficient energy to overcome the activation energy barrier.

Question 16

Which of the following is a correct statement about the effect of a catalyst on the energy profile of a reaction?

Accepted Answer

A catalyst lowers the activation energy but does not change the overall energy change ($$\Delta E) of $$the reaction.

Question 17

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

Accepted Answer

The rate is independent of the concentration of the reactant.

Question 18

Which of the following is a real-world example of a heterogeneous catalyst?

Accepted Answer

A catalytic converter in a car exhaust system

Question 19

Which of the following best describes the role of a reaction intermediate?

Accepted Answer

It is produced in one step and consumed in a subsequent step of the mechanism.

Question 20

If the rate constant $$k$$ for a reaction increases from $$1.4 	imes 10$$^{-3}$$ to 2.9$$ 	imes $$10^{-3} as $$the temperature increases from $$3^\circ C to$$ $$13^\circ C$$, which equation would you use to calculate the activation energy $$E_a$$?

Accepted Answer

$$\ln\left(\frac{k_2$}{k_1$}\right) = \frac{E_a}{R}\left(\frac{1}{T_1$} - \frac{1}{T_2$}\right)$$

Chemical Kinetics: Rates and Mechanisms of Chemical Reactions

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