Q: For the reaction $$N_2(g) + 3H_2(g$$) \rightarrow 2NH_3(g)$$, which of the following correctly expresses the normalized rate in terms of the disappearance of H_2$?

$$\text{Rate} = -\frac{1}{3} \frac{d[H_2$]}{dt}$$

Question 1

Which of the following best describes the difference between thermodynamics and kinetics in a chemical reaction?

Accepted Answer

Thermodynamics determines the relative populations of reactants and products at equilibrium, while kinetics determines how fast a reaction proceeds.

Question 2

A reaction is observed to occur only after a spark is applied, even though the reactants are present together. What is the best explanation for this observation?

Accepted Answer

The activation energy barrier must be overcome by the spark to initiate the reaction.

Question 3

Which of the following factors does NOT generally increase the rate of a chemical reaction?

Accepted Answer

Decreasing the surface area of a solid reactant.

Question 4

For the reaction $$2NO(g) + 2H_2(g) ightarrow N_2$(g) + 2H_2O(g)$$, the experimentally determined rate law is $$	ext{Rate} = k[NO]^2[H_2$]. $$What is the overall order of the reaction?

Accepted Answer

Third order

Question 5

The half-life of a first-order reaction is given by $$t_{1/2} = \frac{\ln 2}{k}. $$Which statement is true about the half-life of a first-order reaction?

Accepted Answer

It is constant and independent of the initial concentration.

Question 6

A reaction has a rate law $$	ext{Rate} = k[A]. If $$the initial concentration of $$A is $$doubled, what happens to the initial rate?

Accepted Answer

It doubles.

Question 7

Which of the following is a correct integrated rate law for a second-order reaction with respect to a single reactant $$A$$?

Accepted Answer

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

Question 8

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

Accepted Answer

The activation energy required for the reaction to occur.

Question 9

A catalyst increases the rate of a chemical reaction by:

Accepted Answer

Decreasing the activation energy of the reaction.

Question 10

In a multi-step reaction, which step determines the overall rate of the reaction?

Accepted Answer

The step with the highest activation energy.

Question 11

For the reaction $$N_2(g) + 3H_2(g$$) \rightarrow 2NH_3(g)$$, which of the following correctly expresses the normalized rate in terms of the disappearance of H_2$?

Accepted Answer

$$	ext{Rate} = -\frac{1}{3} \frac{d[H_2$]}{dt}$$

Question 12

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

Accepted Answer

It increases the number of collisions and the fraction of molecules with energy greater than the activation energy.

Question 13

A reaction has the following mechanism:
Step 1: $$A + B \rightleftharpoons C ($$fast)
Step 2: $$C + D \rightarrow E ($$slow)
What is the rate law for the overall reaction if Step 1 is at pre-equilibrium?

Accepted Answer

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

Question 14

Which of the following statements about catalysts is FALSE?

Accepted Answer

Catalysts change the equilibrium position of a reaction.

Question 15

In enzyme kinetics, the steady-state approximation assumes:

Accepted Answer

The concentration of enzyme-substrate complex remains constant.

Question 16

For a zeroth-order reaction, which of the following is true about the rate and the integrated rate law?

Accepted Answer

The rate is independent of the concentration, and $$[A]_t = [A]_0 - kt.$$

Question 17

A reaction is found to have a rate law $$	ext{Rate} = k[NO_2$]^2. $$Which of the following is a possible mechanism for this reaction?

Accepted Answer

A single bimolecular elementary step involving two $$NO_2$$ molecules.

Question 18

If the rate constant $$k$$ for a reaction increases by a factor of 10 when the temperature is raised from 300 K to 310 K, what can be inferred about the activation energy?

Accepted Answer

The activation energy is likely to be high, since $$k is $$very sensitive to temperature.

Question 19

Which of the following best describes the molecularity of an elementary reaction?

Accepted Answer

The number of molecules, atoms, or ions that collide in a single elementary step.

Chemical Kinetics: Rates, Mechanisms, and Catalysis

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