Question 1

Which of the following statements best explains why the anti-conformation of butane is more prevalent at equilibrium than the gauche conformation?

Accepted Answer

The anti-conformation has lower strain energy, making it more stable and thus favored at equilibrium.

Question 2

Given the relationship $$\Delta G^\circ = -RT \ln K_{eq}$$, what is the value of $$K_{eq}$$ when $$\Delta G^\circ = 0 at 298 K$$?

Accepted Answer

$$K_{eq} = 1$$

Question 3

Which of the following changes will make a chemical reaction more thermodynamically favorable according to $$\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ$$?

Accepted Answer

A negative $$\Delta H^\circ$$ and a positive $$\Delta S^\circ$$

Question 4

Rotation around a single bond in butane is described as entropically neutral. What is the value of $$\Delta S^\circ$$ for the process anti $$\rightarrow$$ gauche?

Accepted Answer

$$\Delta S^\circ = 0$$

Question 5

Which statement correctly describes the activation energy ($$E_a) $$for rotation around a double bond compared to a single bond?

Accepted Answer

The activation energy for rotation around a double bond is much higher because rotation breaks the $$\pi$$ bond.

Question 6

If a chemical reaction has $$\Delta G^\circ \u003e 0$$, which of the following is true about the equilibrium constant $$K_{eq}$$?

Accepted Answer

$$K_{eq} \u003c 1$$

Question 7

Which of the following best describes the effect of molecular strain on enthalpy ($$\Delta H^\circ) $$and stability?

Accepted Answer

Increased strain raises $$\Delta H^\circ$$ and decreases stability.

Question 8

A reaction has $$\Delta H^\circ = -50 kJ/$$mol and $$\Delta S^\circ = -100 J/($$mol\cdot K). At what temperature (in K) does the reaction become non-spontaneous ($$\Delta G^\circ = 0$$)?

Accepted Answer

$$T = 500 K$$

Question 9

Which of the following is true regarding the rate of rotation from gauche to anti conformation in butane?

Accepted Answer

It is faster than the rate from anti to gauche because the anti conformation is more stable.

Question 10

Which of the following best describes the relationship between Gibbs free energy and the equilibrium constant?

Accepted Answer

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

Question 11

In the halogenation of alkanes, which type of reaction occurs?

Accepted Answer

Substitution reaction where an alkyl hydrogen is replaced by a halogen.

Question 12

A chemist is analyzing a reaction with $$\Delta H^\circ = +20 kJ/$$mol and $$\Delta S^\circ = +100 J/($$mol\cdot K). At $$T = 298 K$$, is the reaction spontaneous?

Accepted Answer

Yes, because $$\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ is $$negative.

Question 13

Which of the following is true about bond formation and enthalpy?

Accepted Answer

Bond formation is favorable and releases energy, resulting in $$\Delta H^\circ \u003c 0.$$

Question 14

If a reaction has a high activation energy ($$E_a$$), what can be inferred about its rate?

Accepted Answer

The reaction will be slow.

Question 15

Which of the following scenarios will result in a decrease in molecular stability?

Accepted Answer

An increase in strain energy.

Question 16

A reaction has $$\Delta G^\circ = -10 kJ/$$mol at 298 K. What can be said about the equilibrium constant $$K_{eq}$$?

Accepted Answer

$$K_{eq} \u003e 1$$

Question 17

Which of the following is true about the entropy change ($$\Delta S^\circ) $$when one molecule is converted to another (e.g., anti to gauche conformation)?

Accepted Answer

$$\Delta S^\circ is $$approximately zero.

Question 18

Which of the following best describes the transition state in a chemical reaction?

Accepted Answer

It is the highest energy state in a molecular collision that leads to a reaction.

Question 19

In a reaction coordinate diagram for butane conformational equilibrium, which conformation would you expect to have the lowest energy?

Accepted Answer

Anti-conformation

Chapter 5 – Chemical Reaction Analysis: Thermodynamics & Kinetics

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