Question 1

Which of the following best describes the role of a radical inhibitor in a free radical chain reaction?

Accepted Answer

It reacts with radicals to terminate the chain reaction.

Question 2

During the free radical halogenation of methane, which step is responsible for the majority of product formation?

Accepted Answer

Propagation

Question 3

Which equation correctly relates free energy change ($$\Delta G$$), enthalpy change ($$\Delta H$$), and entropy change ($$\Delta S) at $$temperature $$T$$?

Accepted Answer

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

Question 4

In the context of reaction kinetics, what does the activation energy ($$E_a) $$represent?

Accepted Answer

The minimum energy required for reactants to reach the transition state.

Question 5

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

Accepted Answer

It is a high-energy, short-lived configuration where bonds are partially formed and broken.

Question 6

A student is studying the free radical halogenation of ethane. Which of the following is a reactive intermediate in this reaction?

Accepted Answer

Ethyl radical ($$\mathrm{C_2H_5\cdot})$$

Question 7

Which of the following best explains why bromine is more selective than chlorine in free radical halogenation reactions?

Accepted Answer

Bromine's reaction is more endothermic, favoring formation of the most stable radical.

Question 8

Which of the following is true regarding the entropy change ($$\Delta S) in a $$reaction where two molecules combine to form one product?

Accepted Answer

$$\Delta S is $$negative because disorder decreases.

Question 9

Consider the following reaction mechanism:

1. $$\mathrm{Cl_2$ \rightarrow 2Cl\cdot}
2$$. $$\mathrm{Cl\cdot + CH_4$ \rightarrow CH_3$\cdot + HCl}
3$$. $$\mathrm{CH_3$\cdot + Cl_2$ \rightarrow CH_3Cl + Cl\cdot}$$

Which step is the initiation step?

Accepted Answer

Step 1

Question 10

A reaction has an activation energy of $$50\ \mathrm{kJ/mol}$$ and occurs at $$298\ \mathrm{K}. If a $$catalyst lowers the activation energy to $$30\ \mathrm{kJ/mol}$$, what is the most likely effect on the reaction rate?

Accepted Answer

The reaction rate will increase.

Question 11

Which of the following is a correct definition of a free radical?

Accepted Answer

An atom or molecule with an unpaired electron.

Question 12

In a free radical chain reaction, which process is responsible for the formation of side products and the eventual slowing of the reaction?

Accepted Answer

Termination

Question 13

Which of the following best describes the effect of a radical inhibitor on the overall free energy change ($$\Delta G) of a $$reaction?

Accepted Answer

It does not affect $$\Delta G$$ but slows the reaction by removing radicals.

Question 14

Which of the following is the correct expression for the rate constant $$k in $$terms of activation energy $$E_a$$ and temperature $$T$$ according to the Arrhenius equation?

Accepted Answer

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

Question 15

A chemist observes that a reaction mixture contains a high concentration of reactive intermediates but the product formation is slow. Which factor is most likely responsible?

Accepted Answer

Presence of a radical inhibitor.

Question 16

Which of the following statements about the propagation step in a free radical chain reaction is correct?

Accepted Answer

It generates new radicals and sustains the reaction.

Question 17

If the entropy change ($$\Delta S) $$for a reaction is negative and the enthalpy change ($$\Delta H) is $$also negative, under what condition will the reaction be spontaneous?

Accepted Answer

At low temperatures

Question 18

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

Accepted Answer

It is present in high concentration at equilibrium.

Question 19

A student proposes that increasing the concentration of a radical inhibitor will increase the yield of the desired product in a free radical halogenation. Is this correct?

Accepted Answer

No, because inhibitors terminate radicals and decrease product yield.

Question 20

Which of the following best describes the relationship between the transition state and activation energy in a chemical reaction?

Accepted Answer

The activation energy is the energy required to reach the transition state from the reactants.

Organic Chemistry: Chemical Reactions, Stereochemistry, and Nucleophilic Substitution

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