Q: Which equation is used to calculate the standard entropy change for a reaction?

$$\Delta S^\circ = \sum n \Delta S^\circ (\text{products}) - \sum m \Delta S^\circ (\text{reactants})$$

Q: Given $$\Delta G^\circ = -33,300 J/$$mol for the Haber process at 298 K, what is the equilibrium constant $$K at $$this temperature? ($$R = 8.314 J/$$mol·K)

$$K = e$$^{13.4}$$ \approx 6.86 \times 10^5$

Question 1

Which of the following statements best describes the First Law of Thermodynamics?

Accepted Answer

The total energy of the universe is a constant; energy can be transferred or converted but not created or destroyed.

Question 2

Which process is spontaneous under standard conditions?

Accepted Answer

Rusting of iron in moist air

Question 3

Which equation correctly relates entropy to the number of microstates?

Accepted Answer

$$S = k_B \ln W$$

Question 4

For the reaction: $$N_2(g) + 3$$ $$H_2(g$$) \rightarrow 2 $$NH_3(g$$)$$ at 298 K, given $$\Delta H^\circ = -92.38$$ kJ and $$\Delta S^\circ = -198.3$$ J/K, what is $$\Delta G^\circ$$ at 25 $$^\circ$$C?

Accepted Answer

$$-33.3 kJ$$

Question 5

Which of the following changes will increase the entropy of a system?

Accepted Answer

Increasing the number of independently moving molecules

Question 6

Which of the following is true for a reversible process?

Accepted Answer

It maximizes the work done by the system on the surroundings.

Question 7

According to the Third Law of Thermodynamics, what is the entropy of a perfect crystal at absolute zero?

Accepted Answer

$$S = k_B \ln W$$, where $$W = 1$$, so $$S = 0$$

Question 8

Which of the following reactions would have a negative $$\Delta S$$?

Accepted Answer

$$Ag^+(aq) + Cl^-(aq) \rightarrow AgCl(s)$$

Question 9

Which of the following best explains why the entropy of $$HCl(g) is $$greater than that of $$NaCl(s) at 25$$ $$^\circC$$?

Accepted Answer

Gases have more freedom of motion and more possible microstates than solids.

Question 10

Which equation is used to calculate the standard entropy change for a reaction?

Accepted Answer

$$\Delta S^\circ = \sum n \Delta S^\circ (	ext{products}) - \sum m \Delta S^\circ (	ext{reactants})$$

Question 11

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

Accepted Answer

For $$T \u003e 250 K$$

Question 12

Which of the following is true for a process where $$\Delta G \u003c 0$$?

Accepted Answer

The process is spontaneous in the forward direction.

Question 13

Given $$\Delta G^\circ = -33,300 J/$$mol for the Haber process at 298 K, what is the equilibrium constant $$K at $$this temperature? ($$R = 8.314 J/$$mol·K)

Accepted Answer

$$K = e$$^{13.4}$$ \approx 6.86 	imes 10^5$

Question 14

Which of the following best describes the effect of increasing temperature on the entropy of a system?

Accepted Answer

Entropy increases because there are more possible kinetic energy values and microstates.

Question 15

Which of the following is NOT a type of molecular motion that contributes to entropy?

Accepted Answer

Ionic

Question 16

For the reaction $$2 NO(g) + O_2$(g) \rightarrow 2 NO_2$(g)$$, what happens to the entropy of the system?

Accepted Answer

Entropy decreases because the number of gas molecules decreases.

Question 17

Which of the following equations relates the standard free energy change to the equilibrium constant?

Accepted Answer

$$\Delta G^\circ = -RT \ln K$$

Question 18

Which of the following is true for a process at equilibrium?

Accepted Answer

$$\Delta G = 0$$

Question 19

Which of the following best describes why ice melts spontaneously above 0 $$^\circC$$?

Accepted Answer

The increase in entropy outweighs the enthalpy change at higher temperature.

Question 20

Which of the following is a correct statement about spontaneous processes?

Accepted Answer

A process that is spontaneous in one direction is nonspontaneous in the reverse direction.

Chapter 19: Chemical Thermodynamics – Structured Study Notes

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