Question 1

Which of the following statements best describes the difference between homolytic and heterolytic bond cleavage?

Accepted Answer

Homolytic cleavage results in the formation of free radicals, while heterolytic cleavage results in the formation of ions.

Question 2

Consider the following reaction: $$\mathrm{CH_4$ + Cl_2$ \xrightarrow{hv} CH_3Cl + HCl}. $$Which step in the free radical chain mechanism is responsible for generating the first chlorine radical?

Accepted Answer

Initiation step

Question 3

Which of the following best describes the rate-limiting step in a multistep reaction?

Accepted Answer

The step with the highest activation energy.

Question 4

According to the Hammond Postulate, the transition state of an exothermic reaction most closely resembles:

Accepted Answer

The reactants in both energy and structure.

Question 5

Which of the following is the correct order of stability for free radicals?

Accepted Answer

Tertiary $$\u003e$$ Secondary $$\u003e$$ Primary $$\u003e$$ Methyl

Question 6

In the chlorination of methane, which of the following is a propagation step?

Accepted Answer

$$\mathrm{CH_3$\cdot + Cl_2$ \rightarrow CH_3Cl + Cl\cdot}$$

Question 7

Which of the following best explains why bromination is more selective than chlorination in the halogenation of alkanes?

Accepted Answer

Bromination is endothermic, so the transition state resembles the products, making selectivity higher.

Question 8

Which of the following is NOT a characteristic of a reactive intermediate?

Accepted Answer

It is present in high concentrations during the reaction.

Question 9

A reaction has an activation energy $$E_a = +17\ \mathrm{kJ/mol}$$ and $$\Delta H^\circ = +4\ \mathrm{kJ/mol}. $$Which of the following best describes the reaction-energy diagram?

Accepted Answer

The transition state is closer in energy to the products.

Question 10

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

Accepted Answer

$$\mathrm{Cl\cdot + Cl\cdot \rightarrow Cl_2$}$$

Question 11

Which of the following best describes the role of thermodynamics in the study of chemical reactions?

Accepted Answer

It allows us to compare the stability of reactants and products and predict equilibrium.

Question 12

Which of the following is the correct representation of a carbene?

Accepted Answer

$$\mathrm{CH_2$:}$$

Question 13

Which of the following statements about the Hammond Postulate is correct?

Accepted Answer

The structure of a transition state resembles the closest stable species in energy.

Question 14

In the context of free radical halogenation, why is the abstraction of a hydrogen atom by a chlorine radical considered a propagation step?

Accepted Answer

It generates a new radical and continues the chain reaction.

Question 15

Which of the following best explains why tertiary free radicals are more stable than primary free radicals?

Accepted Answer

Tertiary radicals have more alkyl groups that can donate electron density by hyperconjugation and induction.

Question 16

Which of the following is true about the energy profile of an exothermic reaction?

Accepted Answer

The transition state is closer in energy and structure to the reactants.

Question 17

Which of the following is a correct example of a homolytic cleavage?

Accepted Answer

$$\mathrm{Cl_2$ \xrightarrow{hv} 2Cl\cdot}$$

Question 18

Which of the following statements about the rate-limiting step is correct?

Accepted Answer

It determines the overall rate of the reaction.

Question 19

Which of the following best describes the effect of increasing the activation energy ($$E_a) of a $$reaction?

Accepted Answer

The reaction rate decreases.

Question 20

Which of the following is a real-life application of free radical chain reactions?

Accepted Answer

The synthesis of chloromethane from methane and chlorine under UV light.

Study Guide: The Study of Chemical Reactions (Organic Chemistry)

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