Question 1

For the reaction $$\mathrm{O_2$} + 4\mathrm{NO_2$} ightarrow 2\mathrm{N_2O_5}$$, the experimentally determined rate law is $$	ext{Rate} = k[\mathrm{NO_2$}]. $$Which of the following statements is TRUE regarding the effect of changing $$[\mathrm{O_2$}] on $$the rate of reaction?

Accepted Answer

Changing $$[\mathrm{O_2$}]$$ will not affect the rate of reaction.

Question 2

A first-order reaction has a rate constant $$k = 0.040\ \mathrm{s}^{-1}. If $$the initial concentration $$[A]_0 is$$ $$0.25\ \mathrm{M}$$, how long will it take for the concentration to decrease by a factor of 50?

Accepted Answer

$$t = 97.8\ \mathrm{s}$$

Question 3

Which integrated rate law correctly describes a zero-order reaction?

Accepted Answer

$$[A]_t = -kt + [A]_0$$

Question 4

Which of the following statements about the half-life of a first-order reaction is correct?

Accepted Answer

The half-life is given by $$t_{1/2} = \dfrac{0.693}{k}$$ and is independent of $$[A]_0.$$

Question 5

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

Accepted Answer

A catalyst decreases the activation energy and changes the reaction mechanism.

Question 6

The Arrhenius equation relates the rate constant $$k to $$the activation energy $$E_a$$ and temperature $$T. $$Which is the correct form of the Arrhenius equation?

Accepted Answer

$$k = Ae$$^{-E_a/(RT)}$$

Question 7

For a reaction with the rate law $$	ext{Rate} = k[\mathrm{NO}]^2[\mathrm{Br}_2]$$, which of the following mechanisms is most likely?

Accepted Answer

A two-step mechanism where the slow step involves 2 NO molecules and the fast step involves Br$$_2.$$

Question 8

Which statement about the rate-determining step in a multistep reaction mechanism is correct?

Accepted Answer

The rate-determining step is the slowest step and controls the overall reaction rate.

Question 9

In the Maxwell-Boltzmann distribution, what does increasing the temperature do to the fraction of molecules with energy greater than or equal to the activation energy $$E_a$$?

Accepted Answer

It increases the fraction of molecules with energy $$\geq E_a.$$

Question 10

Which of the following is TRUE about intermediates in a reaction mechanism?

Accepted Answer

Intermediates are formed in one elementary step and consumed in another.

Question 11

A reaction is found to have a rate law $$	ext{Rate} = k[\mathrm{NO}_2]^2. $$Which of the following mechanisms is consistent with this rate law?

Accepted Answer

A single elementary step involving two NO$$_2$$ molecules.

Question 12

Which of the following is a correct statement about heterogeneous catalysis?

Accepted Answer

The catalyst is in a different phase than the reactants.

Question 13

Given the reaction coordinate diagram, what does the highest point on the diagram represent?

Accepted Answer

The transition state.

Question 14

Which of the following is the correct expression for the half-life of a second-order reaction?

Accepted Answer

$$t_{1/2} = \dfrac{1}{k[A]_0}$$

Question 15

If a reaction is endothermic, which of the following is TRUE about the energy change $$\Delta E$$?

Accepted Answer

$$\Delta E is $$positive.

Question 16

Which of the following is NOT a possible molecularity for an elementary reaction?

Accepted Answer

Tetramolecular

Question 17

For a reaction with a slow initial step followed by a fast step, which step determines the overall rate law?

Accepted Answer

The slow step

Question 18

Which of the following is TRUE about the rate constant $$k$$ for a reaction?

Accepted Answer

It is independent of reactant concentrations and depends only on temperature.

Question 19

Which of the following is a correct statement about the effect of a catalyst on the reaction coordinate diagram?

Accepted Answer

A catalyst decreases the activation energy barrier.

Question 20

Which of the following is the correct relationship for calculating activation energy $$E_a$$ using the Arrhenius equation at two temperatures?

Accepted Answer

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

Chemical Kinetics and Reaction Mechanisms – General Chemistry II Study Notes

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