Question 1

Which of the following statements best describes the difference between thermodynamics and kinetics in the study of chemical reactions?

Accepted Answer

Thermodynamics studies the energy changes and equilibrium position of a reaction, while kinetics studies the rate and mechanism of the reaction.

Question 2

The chlorination of methane is initiated by which of the following processes?

Accepted Answer

Homolytic cleavage of a Cl-Cl bond by absorption of a photon

Question 3

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

Accepted Answer

A stable molecule reacts with a free radical to produce another free radical and a product.

Question 4

Given the following bond dissociation energies: $$\mathrm{Cl-Cl} = +242\ \mathrm{kJ/mol}$$, $$\mathrm{CH_3$-H} = +435\ \mathrm{kJ/mol}$$, $$\mathrm{H-Cl} = -431\ \mathrm{kJ/mol}$$, $$\mathrm{CH_3$-Cl} = -351\ \mathrm{kJ/mol}$$, what is the overall enthalpy change ($$\Delta H^\circ) $$for the reaction $$\mathrm{CH_4$} + \mathrm{Cl_2$} \rightarrow \mathrm{CH_3Cl} + \mathrm{HCl}$$?

Accepted Answer

$$\Delta H^\circ = -105\ \mathrm{kJ/mol}$$

Question 5

Which of the following is true regarding the activation energy ($$E_a) $$and reaction rate for halogenation of methane?

Accepted Answer

As $$E_a$$ increases, the reaction rate decreases.

Question 6

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

Accepted Answer

Tertiary radicals have more hyperconjugation and inductive stabilization from adjacent alkyl groups.

Question 7

Which of the following is the correct rate law for a reaction where the rate-determining step involves one molecule of A and two molecules of B?

Accepted Answer

$$	ext{rate} = k_r [A][B]^2$$

Question 8

Which of the following statements about the transition state in a reaction energy diagram is correct?

Accepted Answer

The transition state corresponds to the highest energy point along the reaction coordinate.

Question 9

A radical inhibitor is added to food products to prevent spoilage. What is the primary function of a radical inhibitor in this context?

Accepted Answer

It combines with free radicals to form stable molecules, stopping the chain reaction.

Question 10

Which of the following best describes the selectivity of halogenation reactions with respect to the type of hydrogen atom replaced?

Accepted Answer

Bromination is highly selective for tertiary hydrogens, while chlorination is less selective.

Question 11

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

Accepted Answer

$$\Delta G^\circ = -RT \ln K_{eq}$$

Question 12

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

Accepted Answer

Two chlorine radicals combine to form Cl$$_2.$$

Question 13

Which of the following best describes the effect of temperature on the rate constant $$k$$ according to the Arrhenius equation?

Accepted Answer

As temperature increases, $$k$$ increases.

Question 14

Which of the following intermediates is most stabilized by resonance?

Accepted Answer

Allylic carbocation

Question 15

Which of the following statements about carbanions is correct?

Accepted Answer

Carbanions are destabilized by alkyl substituents.

Question 16

Which of the following best explains why the reaction $$\mathrm{CH_4$} + \mathrm{Cl_2$} \rightarrow \mathrm{CH_3Cl} + \mathrm{HCl} is $$considered exothermic?

Accepted Answer

The bonds formed in the products are stronger than the bonds broken in the reactants.

Question 17

Which of the following is true about the rate-determining step in a multistep reaction?

Accepted Answer

It is the slowest step with the highest activation energy.

Question 18

Which of the following best describes the structure and reactivity of a carbene?

Accepted Answer

A carbene is neutral, has a lone pair and an empty p orbital, and can act as both a nucleophile and an electrophile.

Question 19

Which of the following best explains why free-radical bromination is more selective than chlorination?

Accepted Answer

Bromination has a higher activation energy, so it favors the formation of the most stable radical intermediate.

Thermodynamics and Kinetics of Free Radical Halogenation of Alkanes

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