Question 1

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

Accepted Answer

Homolytic cleavage results in both atoms retaining one electron from the bond, while heterolytic cleavage results in one atom taking both electrons.

Question 2

Given the following reaction:

$$\mathrm{CH_4$} + \mathrm{Br_2$} \rightarrow \mathrm{CH_3Br} + \mathrm{HBr}$$

Using the bond dissociation energies: $$\mathrm{C-H} (397 kJ/$$mol), $$\mathrm{Br-Br} (193 kJ/$$mol), $$\mathrm{C-Br} (285 kJ/$$mol), $$\mathrm{H-Br} (368 kJ/$$mol), calculate $$\Delta H$$ for the reaction.

Accepted Answer

$$\Delta H = (397 + 193) - (285 + 368) = -63\ \mathrm{kJ/mol}$$

Question 3

Which of the following scenarios would most likely result in a positive entropy change ($$\Delta S_{sys} \u003e 0) $$for a chemical reaction?

Accepted Answer

A cyclic compound is converted into an acyclic compound.

Question 4

Which of the following best explains why a reaction with a negative $$\Delta G$$ does not always proceed rapidly?

Accepted Answer

The reaction may have a high activation energy ($$E_a$$), making it kinetically slow.

Question 5

Which of the following is the correct relationship between the equilibrium constant ($$K_{eq}) $$and the standard free energy change ($$\Delta G^\circ$$)?

Accepted Answer

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

Question 6

A reaction is found to be exothermic and has an increase in entropy ($$\Delta H  0). $$What can be said about the spontaneity of this reaction at all temperatures?

Accepted Answer

The reaction will be spontaneous at all temperatures.

Question 7

Which of the following factors does NOT affect the rate constant ($$k) of a $$chemical reaction?

Accepted Answer

The equilibrium constant ($$K_{eq}) of $$the reaction.

Question 8

Which of the following statements about nucleophiles and electrophiles is correct?

Accepted Answer

Nucleophiles are electron-rich species that donate a pair of electrons, while electrophiles are electron-deficient species that accept a pair of electrons.

Question 9

Which of the following best describes the Hammond Postulate?

Accepted Answer

The structure of a transition state resembles the species (reactant or product) to which it is closer in energy.

Question 10

Which of the following is TRUE regarding the use of curved arrows in organic reaction mechanisms?

Accepted Answer

The tail of the arrow starts on a pair of electrons, and the head ends on an atom where a bond is formed or a lone pair is created.

Question 11

Which of the following statements about carbocation rearrangements is correct?

Accepted Answer

Carbocation rearrangements only occur if a more stable carbocation can be formed.

Question 12

Which of the following is NOT a common pattern of electron movement in polar organic reactions?

Accepted Answer

Radical chain propagation.

Question 13

A reaction is found to be endergonic ($$\Delta G \u003e 0). $$Which of the following is true?

Accepted Answer

The reaction is nonspontaneous and favors the reactants.

Question 14

Which of the following best explains why the loss of a leaving group is generally reversible?

Accepted Answer

Most leaving groups can act as nucleophiles and re-attack the substrate.

Question 15

Which of the following is a correct statement about the effect of temperature on reaction rate?

Accepted Answer

Increasing temperature increases the reaction rate by increasing the number of molecules with sufficient energy to overcome the activation energy.

Question 16

Which of the following is NOT a factor that affects the rate of a chemical reaction?

Accepted Answer

The sign of $$\Delta G$$ for the reaction.

Question 17

Which of the following statements about catalysts is correct?

Accepted Answer

A catalyst provides an alternative pathway with a lower activation energy and is not consumed in the reaction.

Question 18

Which of the following is TRUE regarding the reversibility of proton transfers in acid-base reactions?

Accepted Answer

All proton transfers are reversible, unless the $$pK_a$$ difference is 10 units or more.

Question 19

Which of the following best describes the difference between a transition state and an intermediate on an energy diagram?

Accepted Answer

A transition state is an energy maximum and cannot be isolated, while an intermediate is an energy minimum and can sometimes be observed.

Chapter 6: Chemical Reactivity and Mechanisms – Thermodynamics, Kinetics, and Reaction Mechanisms in Organic Chemistry

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