Question 1

Which of the following best describes the role of light in the chlorination of methane?

Accepted Answer

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

Question 2

In the free-radical chain reaction mechanism for methane chlorination, which step is responsible for generating the first reactive intermediate?

Accepted Answer

Initiation

Question 3

Which of the following equations correctly expresses the equilibrium constant $$K_{eq}$$ for the reaction $$aA + bB \rightleftharpoons cC + dD$$?

Accepted Answer

$$K_{eq} = \frac{[C]^c [D]^d}{[A]^a [B]^b}$$

Question 4

A reaction with a negative $$\Delta G^\circ is$$:

Accepted Answer

Spontaneous and favorable

Question 5

Which of the following best describes a homolytic cleavage?

Accepted Answer

Each atom receives one electron from the bond, forming free radicals.

Question 6

Given the reaction $$CH_4$$ + $$Cl_2$$ ightarrow CH_3Cl + HCl$$, and K$$_{eq} = 1.1 	imes $$10^{19}$$, calculate $$\Delta G^\circ at$$ $$T = 298 K $$using $$\Delta G^\circ = -2.303RT \log K_{eq}$$ and $$R = 8.314 J/($$mol·K). Which value is closest to the answer?

Accepted Answer

$$-109 kJ/$$mol

Question 7

Which statement about free radicals is correct?

Accepted Answer

Free radicals are reactive species with odd numbers of electrons.

Question 8

During the propagation step of methane chlorination, what is the role of the chlorine atom?

Accepted Answer

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

Question 9

Which of the following is true regarding the factors that determine $$\Delta G^\circ$$?

Accepted Answer

$$\Delta G^\circ$$ depends on both enthalpy ($$\Delta H^\circ) $$and entropy ($$\Delta S^\circ) $$changes.

Question 10

Which of the following best describes the termination step in a free-radical chain reaction?

Accepted Answer

Two free radicals combine to form a non-radical product.

Question 11

Which of the following statements about bond-dissociation enthalpy (BDE) is correct?

Accepted Answer

BDE is the energy required to break a bond homolytically in a gaseous molecule.

Question 12

Which of the following is a correct expression for the free energy change of a reaction?

Accepted Answer

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

Question 13

Which of the following best describes entropy ($$\Delta S^\circ) in a $$chemical reaction?

Accepted Answer

Entropy is the change in randomness, disorder, or freedom of movement.

Question 14

In the energy diagram of an exothermic reaction, which of the following is true?

Accepted Answer

The reactants have higher energy than the products.

Question 15

Which of the following is a correct statement about the propagation steps in the chlorination of methane?

Accepted Answer

The first propagation step forms a methyl radical and HCl.

Question 16

Which of the following is true about the effect of temperature on the equilibrium constant $$K_{eq}$$ and $$\Delta G^\circ$$?

Accepted Answer

Increasing temperature can affect $$K_{eq}$$ and $$\Delta G^\circ$$ depending on the sign of $$\Delta H^\circ$$ and $$\Delta S^\circ.$$

Question 17

Which of the following is a correct statement about the enthalpy change ($$\Delta H^\circ) in a $$chemical reaction?

Accepted Answer

Endothermic reactions absorb heat and have positive $$\Delta H^\circ.$$

Question 18

Which of the following is true about the composition of products as a function of $$\Delta G^\circ at 25$$°C?

Accepted Answer

As $$\Delta G^\circ$$ becomes more negative, the percentage of products at equilibrium increases.

Question 19

Which of the following statements about the mechanism of methane chlorination is correct?

Accepted Answer

The overall reaction is $$CH_4$$ + $$Cl_2$$ \rightarrow CH_3Cl + HCl$$.

Organic Chemistry: The Study of Chemical Reactions and Free-Radical Mechanisms

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