Question 1

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

Accepted Answer

It involves the homolytic cleavage of a chlorine molecule to generate two chlorine atoms.

Question 2

Given the reaction $$\mathrm{CH_4$ + Cl_2$ \rightarrow CH_3Cl + HCl}$$, which of the following best explains why this reaction is highly favorable at room temperature?

Accepted Answer

The reaction has a large negative $$\Delta G^\circ$$, indicating it is spontaneous.

Question 3

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

Accepted Answer

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

Question 4

In the context of free-radical halogenation, why is bromination of alkanes more selective than chlorination?

Accepted Answer

Bromination has a higher activation energy and is more endothermic, so the transition state resembles the product, making the reaction more selective.

Question 5

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

Accepted Answer

Increasing temperature increases $$k_r$$ because more molecules have energy greater than $$E_a.$$

Question 6

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

Accepted Answer

Tertiary \u003e Secondary \u003e Primary \u003e Methyl

Question 7

A reaction has $$\Delta H^\circ = +4 kJ/$$mol and $$E_a = +17 kJ/$$mol. Which of the following best describes the energy diagram for this reaction?

Accepted Answer

The products are 4 kJ/mol higher in energy than the reactants, and the transition state is 17 kJ/mol above the reactants.

Question 8

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

Accepted Answer

It is the step with the highest activation energy ($$E_a).$$

Question 9

Which of the following best explains why radical inhibitors such as vitamin E are important in biological systems?

Accepted Answer

They react with free radicals to form stable molecules, preventing chain reactions that can damage cells.

Question 10

Which of the following is the correct rate law for a reaction $$A + B \rightarrow C + D if $$the reaction is first order in $$A$$ and second order in $$B$$?

Accepted Answer

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

Question 11

Which of the following best describes the effect of entropy ($$\Delta S^\circ) on $$the spontaneity of a reaction?

Accepted Answer

A positive $$\Delta S^\circ$$ increases the likelihood that a reaction is spontaneous.

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 explains why tertiary hydrogens are more reactive than primary hydrogens in free-radical halogenation?

Accepted Answer

The tertiary radical formed is more stable due to hyperconjugation and inductive effects.

Question 14

Which of the following is the correct expression for the rate constant $$k_r in $$terms of activation energy $$E_a$$ and temperature $$T$$?

Accepted Answer

$$k_r = A e$$^{-E_a/RT}$$

Question 15

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

Accepted Answer

A carbene has a neutral carbon with a lone pair and a vacant p orbital, allowing it to act as both a nucleophile and an electrophile.

Question 16

Which of the following best explains the Hammond postulate?

Accepted Answer

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

Question 17

Which of the following is true about the stability of carbanions?

Accepted Answer

Methyl carbanions are more stable than tertiary carbanions.

Question 18

Which of the following is a real-life application of radical inhibitors?

Accepted Answer

They are added to foods to prevent spoilage by stopping radical chain reactions.

Chapter 4: The Study of Chemical Reactions – Thermodynamics, Kinetics, and Reaction Mechanisms

Guida di studio - Domande di pratica

Study guide - Flashcard