Question 1

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

Accepted Answer

A catalyst provides an alternative reaction pathway with a lower activation energy, increasing the reaction rate.

Question 2

Given the reaction mechanism:
Step 1: NO2 (g) + NO2 (g) $$\xrightarrow{k_1$} NO3 (g) + NO (g) ($$slow)
Step 2: NO3 (g) + CO (g) $$\xrightarrow{k_2$} NO2 (g) + CO2 (g) ($$fast)
What is the rate law for the overall reaction?

Accepted Answer

$$	ext{rate} = k[NO_2$]^2$$

Question 3

Which statement about reaction intermediates is correct?

Accepted Answer

Intermediates are produced in one step and consumed in a subsequent step of the mechanism.

Question 4

The Arrhenius equation is $$k = Ae$$^{-E_a/RT}$$. If the activation energy E_a$ is increased, what happens to the rate constant k$ (assuming all other factors remain constant)?

Accepted Answer

The rate constant $$k$$ decreases.

Question 5

Which of the following is a correct example of heterogeneous catalysis?

Accepted Answer

Hydrogenation of ethylene on a platinum surface.

Question 6

A reaction is found to have a rate law $$	ext{rate} = k[A][B]. $$Which of the following statements is true about the molecularity of the elementary step if this is an elementary reaction?

Accepted Answer

The elementary step is bimolecular.

Question 7

In the context of enzyme catalysis, what does the 'lock-and-key' model describe?

Accepted Answer

The enzyme's active site is complementary in shape to a specific substrate, allowing selective binding.

Question 8

Which of the following best explains why termolecular elementary steps are rare?

Accepted Answer

They require three reactant particles to collide simultaneously, which is statistically unlikely.

Question 9

The half-life for a first-order reaction is given by $$t_{1/2} = \frac{0.693}{k}. If $$the rate constant $$k is $$doubled, what happens to the half-life?

Accepted Answer

The half-life is halved.

Question 10

Which of the following is NOT a characteristic of a catalyst?

Accepted Answer

It changes the equilibrium constant of the reaction.

Question 11

In a two-step reaction, if the first step has a much higher activation energy than the second, which of the following is true?

Accepted Answer

The first step is the rate-determining step.

Question 12

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

Accepted Answer

It is the highest energy point along the reaction pathway.

Question 13

The Haber–Bosch process for ammonia synthesis is extremely slow without a catalyst. What is the main reason for this?

Accepted Answer

The N–N triple bond in $$N_2 is $$very strong and requires a high activation energy to break.

Question 14

Which of the following is a correct statement about the rate law for an elementary step?

Accepted Answer

The rate law is directly determined by the molecularity of the step.

Question 15

Which of the following is a real-world example of homogeneous catalysis?

Accepted Answer

Ozone depletion catalyzed by chlorine atoms in the atmosphere.

Question 16

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

Accepted Answer

It increases by a factor of four.

Question 17

Which of the following best explains why enzymes are highly selective in the reactions they catalyze?

Accepted Answer

Enzymes have active sites that are complementary in shape to specific substrates.

Question 18

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

Accepted Answer

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

Question 19

In the context of surface catalysis, which of the following steps is NOT typically involved?

Accepted Answer

Dissolving the catalyst in the reaction mixture.

Question 20

Which of the following is true about a valid reaction mechanism?

Accepted Answer

It must reproduce the overall balanced equation and the experimentally determined rate law.

Chemical Kinetics III: Reaction Mechanisms and Catalysis

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