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.

Question 2

Given the equation for Gibbs Free Energy $$G = H - TS$$, which change would make a chemical reaction more spontaneous under standard conditions?

Accepted Answer

A decrease in enthalpy ($$H) $$and an increase in entropy ($$S).$$

Question 3

If the standard change in Gibbs Free Energy ($$\Delta G^\circ) $$for a reaction is positive, what can be said about the equilibrium constant ($$K_{eq}$$)?

Accepted Answer

$$K_{eq} \u003c 1$$

Question 4

Which of the following best describes the relationship between $$\Delta G^\circ$$ and $$K_{eq}$$?

Accepted Answer

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

Question 5

A reaction has $$\Delta H^\circ = -50 kJ/$$mol and $$\Delta S^\circ = -100 J/($$mol\cdot K). At $$T = 298 K$$, what is $$\Delta G^\circ$$ for the reaction?

Accepted Answer

$$\Delta G^\circ = -20.2 kJ/$$mol$$\; ($$since $$\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ)$$

Question 6

Which process is entropically neutral according to the study materials?

Accepted Answer

Rotation around a single bond

Question 7

Why is the activation energy for rotation around a double bond much higher than for a single bond?

Accepted Answer

Rotation around a double bond breaks the $$\pi$$ bond, requiring significant energy.

Question 8

Which of the following statements about bond formation and breaking is correct?

Accepted Answer

Bond formation is favored and has $$\Delta H^\circ \u003c 0.$$

Question 9

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

Accepted Answer

Substitution reaction

Question 10

If a reaction has $$\Delta G^\circ = 0$$, what is the value of $$K_{eq}$$ and what does this mean for the reaction?

Accepted Answer

$$K_{eq} = 1$$; neither side is favored

Question 11

Which factor contributes to a decrease in strain and thus a more stable molecule?

Accepted Answer

Decrease in strain energy

Question 12

A chemist is comparing the rate of rotation from gauche to anti and anti to gauche conformations in butane. Which transition is faster and why?

Accepted Answer

Gauche to anti is faster because it goes from less stable to more stable.

Question 13

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

Accepted Answer

A positive $$\Delta S^\circ$$ makes a reaction more favorable.

Question 14

Which of the following is true regarding the equilibrium between anti and gauche conformations of butane?

Accepted Answer

The equilibrium favors the anti conformation because it is more stable.

Question 15

A reaction coordinate diagram for rotation around a single bond shows a transition state. What does the height of the transition state represent?

Accepted Answer

The activation energy required for the rotation.

Question 16

Which of the following is a correct statement about the activation energy ($$E_a) $$for rotation around a single bond versus a double bond?

Accepted Answer

Activation energy is higher for rotation around a double bond due to $$\pi$$ bond disruption.

Question 17

In a halogenation reaction of alkanes, which atom is typically replaced?

Accepted Answer

A hydrogen atom

Question 18

If a chemical reaction results in the formation of more molecules, what is the expected sign of $$\Delta S^\circ$$ and how does it affect favorability?

Accepted Answer

$$\Delta S^\circ is $$positive; favorability increases.

Question 19

Which of the following is true about the entropy change ($$\Delta S^\circ) $$during rotation between anti and gauche conformations of butane?

Accepted Answer

$$\Delta S^\circ is $$approximately zero because the number of molecules does not change.

Question 20

A student is asked to calculate $$\Delta G^\circ$$ for a reaction at 298 K but is not given the temperature. What value should they use for $$T$$?

Accepted Answer

$$T = 298 K$$

Chapter 5 – Chemical Reaction Analysis: Thermodynamics & Kinetics

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