Question 1

Which of the following best describes the initiation step in the free-radical chlorination of methane?

Accepted Answer

A chlorine molecule cleaves homolytically into two chlorine atoms upon absorption of a photon.

Question 2

Which equation correctly relates the standard free energy change ($$\Delta G^\circ) to $$the equilibrium constant ($$K_{eq}$$)?

Accepted Answer

$$K_{eq} = 10$$^{-\Delta G^\circ/2.3RT}$$

Question 3

In the propagation step of methane chlorination, what is the immediate product when a chlorine atom reacts with methane?

Accepted Answer

Methyl radical and hydrogen chloride

Question 4

Which of the following statements about activation energy ($$\Delta G^\circ_{\ddagger}) is $$correct?

Accepted Answer

A large $$\Delta G^\circ_{\ddagger}$$ means few collisions have enough energy to react, so the reaction is slow.

Question 5

Which of the following best explains why the chlorination of methane is considered a chain reaction?

Accepted Answer

Each propagation step regenerates a reactive intermediate, allowing the reaction to continue.

Question 6

Given the reaction $$\mathrm{CH_4$ + Cl_2$ \rightarrow CH_3Cl + HCl}$$, which of the following is true if $$\Delta G^\circ is $$negative?

Accepted Answer

The reaction is spontaneous and favors products.

Question 7

Which of the following is a termination step in the free-radical chlorination of methane?

Accepted Answer

Two chlorine radicals combine to form $$\mathrm{Cl_2$}.$$

Question 8

Which factor(s) contribute to the standard free energy change ($$\Delta G^\circ) of a $$reaction?

Accepted Answer

Both enthalpy ($$\Delta H^\circ) $$and entropy ($$\Delta S^\circ)$$

Question 9

Which of the following best describes the role of entropy ($$\Delta S^\circ) in $$determining reaction spontaneity?

Accepted Answer

An increase in entropy ($$\Delta S^\circ \u003e 0) $$favors spontaneity, especially at higher temperatures.

Question 10

A reaction has $$\Delta G^\circ = -5.7 kJ/$$mol at 25°C. What is the approximate value of $$K_{eq} at $$this temperature?

Accepted Answer

$$K_{eq} \approx 10$$

Question 11

Which of the following is the correct expression for the equilibrium constant for the reaction $$\mathrm{CH_4$ + Cl_2$ \rightleftharpoons CH_3Cl + HCl}$$?

Accepted Answer

$$K_{eq} = \frac{[CH_3Cl][HCl]}{[CH_4$][Cl_2$]}$$

Question 12

Which of the following best describes the transition state in a reaction energy diagram?

Accepted Answer

The highest energy point along the reaction coordinate.

Question 13

Which of the following is true about the effect of temperature on the spontaneity of a reaction with $$\Delta H^\circ \u003e 0$$ and $$\Delta S^\circ \u003e 0$$?

Accepted Answer

The reaction becomes more spontaneous as temperature increases.

Question 14

Which of the following is a correct statement about bond dissociation energies in the context of free-radical reactions?

Accepted Answer

Breaking a stronger bond requires more energy input.

Question 15

Which of the following is a real-world consequence of free-radical reactions involving chlorine in the atmosphere?

Accepted Answer

Depletion of the ozone layer.

Question 16

Which of the following best describes a propagation step in the free-radical chlorination of methane?

Accepted Answer

A methyl radical reacts with a chlorine molecule to form chloromethane and a chlorine atom.

Question 17

Which of the following is the correct formula for the standard free energy change in terms of enthalpy and entropy?

Accepted Answer

$$\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ$$

Question 18

Which of the following is NOT a possible termination step in a free-radical chain reaction?

Accepted Answer

A methyl radical reacts with a chlorine molecule to form chloromethane.

Question 19

Which of the following best explains why the reaction $$\mathrm{CH_4$ + Cl_2$ \rightarrow CH_3Cl + HCl}$$ has a large equilibrium constant?

Accepted Answer

The reaction is highly exergonic, with a large negative $$\Delta G^\circ.$$

Chapter 4: The Study of Chemical Reactions – Free Energy, Equilibrium, and Activation Energy

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