Question 1

Which of the following best describes the role of light or heat in the halogenation of methane?

Accepted Answer

It initiates the reaction by homolytically cleaving the Cl-Cl bond to generate chlorine radicals.

Question 2

What is the reactive intermediate formed during the chlorination of methane?

Accepted Answer

Radical

Question 3

Which of the following equations correctly relates the standard free energy change ($$\Delta G^0$) to the equilibrium constant (K$$_{eq}$$)?

Accepted Answer

$$\Delta G^0$ = -2.303RT \log K_{eq}$$

Question 4

In the free-radical halogenation of methane, which step is considered a termination step?

Accepted Answer

$$\mathrm{Cl}\cdot + \mathrm{Cl}\cdot \rightarrow \mathrm{Cl}_2$$

Question 5

Given the reaction $$\mathrm{CH}_4 + \mathrm{Cl}_2 ightarrow \mathrm{CH}_3\mathrm{Cl} + \mathrm{HCl}$$ with $$K_{eq} = 1.1 	imes 10$$^{19}$$, what does this value indicate about the reaction?

Accepted Answer

The reaction goes nearly to completion, favoring the products.

Question 6

Which of the following best explains why the equilibrium favors the products when $$\Delta G^0$ is negative?

Accepted Answer

The products are more stable (lower in energy) than the reactants.

Question 7

Which of the following is the correct expression for the equilibrium constant for the reaction $$A + B \rightleftharpoons C + D$$?

Accepted Answer

$$K_{eq} = \frac{[C][D]}{[A][B]}$$

Question 8

Which of the following statements about entropy ($$\Delta S^0$) is correct?

Accepted Answer

$$\Delta S^0$ is positive when the products are more disordered than the reactants.

Question 9

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

Accepted Answer

A chlorine radical abstracts a hydrogen atom from methane, forming HCl and a methyl radical.

Question 10

Which of the following is the correct relationship for the total energy change ($$\Delta G^0$) in a reaction?

Accepted Answer

$$\Delta G^0$ = \Delta H^0$ - T\Delta S^0$

Question 11

Which of the following scenarios would most likely result in a positive entropy change ($$\Delta S^0$)?

Accepted Answer

A single reactant decomposing into two products.

Question 12

In the context of free-radical halogenation, why is the concentration of radicals typically very low during the chain reaction?

Accepted Answer

Radicals are rapidly consumed in propagation steps.

Question 13

Which of the following best explains why a reaction with $$\Delta H^0$ \u003c 0 is $$considered exothermic?

Accepted Answer

Heat is released by the system.

Question 14

A reaction has $$\Delta G^0$ = -2.9$$ kcal/mol at 25$$^\circC. $$What is the approximate value of $$K_{eq}$$?

Accepted Answer

$$K_{eq} \approx 100$$

Question 15

Which of the following is a correct Lewis structure for a methyl radical?

Accepted Answer

$$\cdot \mathrm{CH}_3$$

Question 16

Which of the following statements about the chain reaction mechanism in halogenation is correct?

Accepted Answer

The propagation steps regenerate the reactive intermediate, allowing the reaction to continue.

Question 17

Which of the following best describes the effect of a small change in $$\Delta G^0$ on the equilibrium position?

Accepted Answer

It results in a large change in the relative amounts of reactants and products.

Question 18

Which of the following is true about the enthalpy and entropy contributions to $$\Delta G^0$ at room temperature?

Accepted Answer

The enthalpy term ($$\Delta H^0$) is often the dominant factor in determining $$\Delta $$G^0.$$

Free-Radical Halogenation of Alkanes and Thermodynamics of Organic Reactions

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