Question 1

Which statement best describes a reaction intermediate in a multi-step mechanism?

Accepted Answer

It is a species produced in one elementary step and consumed in a subsequent step, but does not appear in the overall equation.

Question 2

For the reaction: $$NO_2(g) + CO(g$$) \rightarrow NO(g) + $$CO_2(g$$)$$, the experimentally determined rate law is $$Rate = k[$$NO_2$$]^2$$. Which mechanism is consistent with this rate law?

Accepted Answer

A two-step mechanism where the first step is slow: $$NO_2(g$$) + $$NO_2(g$$) \rightarrow $$NO_3(g) + NO(g$$)$$ (slow), NO_3$(g) + CO(g) \rightarrow NO_2$(g) + CO_2$(g) ($$fast)

Question 3

What is the molecularity of the elementary reaction $$A + B \rightarrow products$$?

Accepted Answer

Bimolecular

Question 4

Which of the following rate laws corresponds to a termolecular elementary reaction involving $$A + B + C \rightarrow products$$?

Accepted Answer

$$Rate = k[A][B][C]$$

Question 5

Why are termolecular elementary reactions considered rare?

Accepted Answer

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

Question 6

In a two-step mechanism, if the first step has a higher activation energy ($$E_{a1}) $$than the second ($$E_{a2}$$), what is true about the reaction rate?

Accepted Answer

The first step is the rate-determining step and has a smaller rate constant.

Question 7

Which statement about catalysts is correct?

Accepted Answer

A catalyst provides a pathway with lower activation energy, speeding up both forward and reverse reactions.

Question 8

What is the main difference between a homogeneous and a heterogeneous catalyst?

Accepted Answer

Homogeneous catalysts are in the same phase as the reactants, while heterogeneous catalysts are in a different phase.

Question 9

Which of the following best describes the role of an enzyme in a biological reaction?

Accepted Answer

It provides a pathway with lower activation energy by binding the substrate at its active site.

Question 10

In the enzyme mechanism $$E + S \rightleftharpoons ES \rightarrow E + P$$, what does $$ES$$ represent?

Accepted Answer

The enzyme-substrate complex

Question 11

Which of the following is a plausible reason why a proposed reaction mechanism might be rejected?

Accepted Answer

The developed rate law does not match the experimentally determined rate law.

Question 12

In the ozone depletion mechanism, what role does the chlorine atom ($$Cl\cdot) $$play?

Accepted Answer

It is a homogeneous catalyst that is regenerated after each cycle.

Question 13

Which intermolecular forces are commonly involved in enzyme-substrate binding?

Accepted Answer

Hydrogen bonding, dipole-dipole, and London dispersion forces

Question 14

If a reaction mechanism has a fast initial step and a slow second step, how is the overall rate law determined?

Accepted Answer

By the rate law of the slow step, substituting the intermediate concentration using equilibrium expressions from the fast step

Question 15

Which of the following is true about the effect of a catalyst on a reaction energy diagram?

Accepted Answer

It lowers the activation energy barrier, but does not change the overall energy difference ($$\Delta E) $$between reactants and products.

Question 16

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

Accepted Answer

The catalytic converter in a car, where exhaust gases pass over ceramic beads coated with metals.

Question 17

What is the effect of enzyme inhibitors on biological reactions?

Accepted Answer

They block the active site of the enzyme, preventing substrate binding and reducing reaction rate.

Question 18

Which of the following best explains why ozone in the stratosphere is important?

Accepted Answer

It protects against harmful UV radiation.

Question 19

In the catalytic destruction of ozone, which species is an intermediate?

Accepted Answer

ClO\cdot

Question 20

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

Accepted Answer

It is consumed in the reaction and not regenerated.

Chapter 15 lecture 4

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