Question 1

Which of the following statements best describes the enthalpy change ($$\Delta H) $$for an exothermic reaction?

Accepted Answer

The products are lower in energy than the reactants, and $$\Delta H is $$negative.

Question 2

Bond dissociation energy (BDE) is most closely associated with which type of bond cleavage?

Accepted Answer

Homolytic bond cleavage, resulting in radicals.

Question 3

Given the following bond dissociation energies: $$\mathrm{CH_3$-CH_3$} (368 kJ/$$mol), $$\mathrm{CH_3$-Br} (293 kJ/$$mol), and $$\mathrm{CH_3$-I} (234 kJ/$$mol), which bond is the weakest?

Accepted Answer

$$\mathrm{CH_3$-I}$$

Question 4

A reaction converts one cyclic compound into two acyclic products. What is the expected sign of the entropy change ($$\Delta S) $$for this reaction?

Accepted Answer

Positive, because the number of possible states increases.

Question 5

Which of the following best explains why a gas expands to fill an open container?

Accepted Answer

The entropy ($$\Delta S) $$increases due to more available volume and microstates.

Question 6

Consider the reaction: $$\mathrm{A \rightarrow B + C}. If $$the number of moles increases, what happens to the entropy ($$\Delta S$$)?

Accepted Answer

$$\Delta S$$ increases because there are more possible arrangements.

Question 7

Which of the following is true for an endothermic reaction?

Accepted Answer

Energy is absorbed and $$\Delta H is $$positive.

Question 8

If a reaction has $$\Delta G \u003c 0$$, which of the following statements is correct?

Accepted Answer

The reaction is spontaneous and exergonic.

Question 9

Which equation correctly relates Gibbs free energy to enthalpy and entropy?

Accepted Answer

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

Question 10

A reaction has $$\Delta H = -100 kJ/$$mol and $$\Delta S = -200 J/($$mol\cdot K)$. At what temperature (in K) does the reaction become nonspontaneous?

Accepted Answer

At $$T \u003e 500 K$$

Question 11

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

Accepted Answer

Homolytic cleavage produces radicals, while heterolytic cleavage produces ions.

Question 12

Which of the following reactions would have the greatest increase in entropy ($$\Delta S$$)?

Accepted Answer

$$\mathrm{A \rightarrow B + C}$$

Question 13

If the products of a reaction are more stable than the reactants, which of the following is most likely true?

Accepted Answer

The reaction is exothermic.

Question 14

Which of the following best explains why bond dissociation energy is important in organic reactions?

Accepted Answer

It indicates the amount of energy required to break a bond homolytically.

Question 15

A reaction has $$\Delta H = +50 kJ/$$mol and $$\Delta S = +200 J/($$mol\cdot K). At what temperature will the reaction become spontaneous?

Accepted Answer

At $$T \u003e 250 K$$

Question 16

Which of the following is true about entropy ($$\Delta S) in a $$chemical reaction?

Accepted Answer

Entropy increases when the number of moles of products is greater than reactants.

Question 17

Which statement is correct regarding the energy diagram of an exothermic reaction?

Accepted Answer

The products are lower in energy than the reactants.

Question 18

In the context of molecular orbitals, what must electrons absorb to break a bond?

Accepted Answer

Kinetic energy to overcome the stability of the bond.

Question 19

Which of the following is a correct statement about the relationship between enthalpy and entropy in determining spontaneity?

Accepted Answer

A reaction is spontaneous if $$\Delta G = \Delta H - T\Delta S is $$negative.

Question 20

Which of the following best describes the effect of increasing the volume available to a gas?

Accepted Answer

It increases the entropy of the system.

Thermodynamics in Organic Chemistry: Enthalpy, Entropy, and Bond Dissociation

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