Q: Which process results in a positive change in entropy ($$\Delta S \u003e 0$$)?

Sublimation of iodine: $$\text{I}_2(s) \rightarrow \text{I}_2(g)$$

Q: Which of the following reactions will have a positive $$\Delta S$$?

$$\text{LiCl}(s) \rightarrow \text{LiCl}(aq)$$

Question 1

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

Accepted Answer

The entropy of a pure crystalline substance at absolute zero is zero.

Question 2

Given the reaction: $$2 	ext{C}_4	ext{H}_{10}(g) + 13 	ext{O}_2(g) ightarrow 8 	ext{CO}_2(g) + 10 	ext{H}_2	ext{O}(g)$$, what are the signs of $$\Delta S$$ and $$\Delta H$$?

Accepted Answer

$$\Delta S = $$negative and $$\Delta H = $$negative

Question 3

Which process results in a positive change in entropy ($$\Delta S \u003e 0$$)?

Accepted Answer

Sublimation of iodine: $$	ext{I}_2(s) ightarrow 	ext{I}_2(g)$$

Question 4

Which of the following changes will increase the number of available microstates in a system?

Accepted Answer

Increasing the temperature

Question 5

Calculate the standard entropy change ($$\Delta S^\circ) $$for the reaction: $$2 	ext{C}_2	ext{H}_6(g) + 7 	ext{O}_2(g) ightarrow 4 	ext{CO}_2(g) + 6 	ext{H}_2	ext{O}(g)$$ using the following data: $$S^\circ(	ext{C}_2	ext{H}_6) = 229.5$$, $$S^\circ(	ext{O}_2) = 205.0$$, $$S^\circ(	ext{CO}_2) = 213.6$$, $$S^\circ(	ext{H}_2	ext{O}) = 188.8 ($$all in J/mol·K).

Accepted Answer

$$\Delta S^\circ = -373.4$$

Question 6

Which of the following best describes the relationship between entropy and the number of microstates ($$W) in a $$system?

Accepted Answer

$$S = k \ln W$$

Question 7

For the vaporization of methanol, $$	ext{CH}_3	ext{OH}(l) ightarrow 	ext{CH}_3	ext{OH}(g)$$, at 100$$^\circC ($$above its boiling point), what is the sign of $$\Delta G$$ and is the process spontaneous?

Accepted Answer

Spontaneous, $$\Delta G is $$negative

Question 8

Which of the following reactions will have a positive $$\Delta S$$?

Accepted Answer

$$	ext{LiCl}(s) ightarrow 	ext{LiCl}(aq)$$

Question 9

Which of the following statements is TRUE regarding Gibbs free energy ($$\Delta G) $$and spontaneity?

Accepted Answer

A reaction is spontaneous as written when $$\Delta G \u003c 0$$

Question 10

Which of the following pairs is ordered correctly from lowest to highest entropy?

Accepted Answer

Al(s), Ne(g), N$$_2(g$$), CF$$_4(g)$$

Question 11

Which of the following is a correct statement about the entropy change when oxygen gas dissolves in water: $$	ext{O}_2(g) ightarrow 	ext{O}_2(aq)$$?

Accepted Answer

The entropy change is negative

Question 12

For the reaction $$4 	ext{Fe}(s) + 3 	ext{O}_2(g) ightarrow 2 	ext{Fe}_2	ext{O}_3(s) (as in $$HotHands hand warmers), what are the signs of $$\Delta S$$ and $$\Delta H$$?

Accepted Answer

$$\Delta S = $$negative and $$\Delta H = $$negative

Question 13

Which of the following is TRUE regarding the spontaneity of the HotHands reaction ($$4 	ext{Fe}(s) + 3 	ext{O}_2(g) ightarrow 2 	ext{Fe}_2	ext{O}_3(s)$$)?

Accepted Answer

This reaction is only spontaneous at low temperatures

Question 14

Which of the following is TRUE regarding the entropy of a system as temperature increases?

Accepted Answer

Entropy increases with temperature due to increased molecular motion

Question 15

Which of the following is the correct formula for calculating the standard entropy change for a reaction?

Accepted Answer

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

Question 16

Which of the following best describes the entropy change for the condensation of water vapor to liquid water?

Accepted Answer

The entropy change is negative

Question 17

Which of the following is TRUE regarding the sign of $$\Delta G$$ for a reaction at equilibrium?

Accepted Answer

$$\Delta G = 0$$

Question 18

Which of the following is TRUE regarding the relationship between $$\Delta G$$ and $$\Delta S_{univ}$$ for a spontaneous reaction?

Accepted Answer

For a spontaneous reaction, $$\Delta G is $$negative and $$\Delta S_{univ} is $$positive

Thermodynamics: Entropy, Gibbs Free Energy, and Spontaneity (Ch.19.3–19.6)

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