Q: Which equation correctly describes the entropy change of the surroundings ($$\Delta S_{\text{surr}}) $$for a reaction occurring at constant temperature?

$$\Delta S_{\text{surr}} = -\Delta H_{\text{sys}} / T$$

Q: A reaction has $$\Delta H_{\text{rxn}} = +100\ \text{kJ}$$ and occurs at $$T = 300\ \text{K}. $$What is the value of $$\Delta S_{\text{surr}} in$$ $$\text{J}/\text{K}$$?

$$\Delta S_{\text{surr}} = -333.3\ \text{J}/\text{K}$$

Q: Which statement best explains why freezing of water is spontaneous below $$0^\circ\text{C}$$ but not above?

At low temperature, $$\Delta S_{\text{surr}} is $$large and positive, dominating the negative $$\Delta S_{\text{sys}}.$$

Q: Given $$\Delta H = -150\ \text{kJ}$$ and $$\Delta S = -100\ \text{J}/\text{K}$$, at what temperature does the reaction become nonspontaneous?

$$T = 150,000\ \text{J} / 100\ \text{J}/\text{K} = 1500\ \text{K}$$

Q: Which equation relates Gibbs free energy to entropy change of the universe?

$$\Delta G = -T\Delta S_{\text{univ}}$$

Q: Which of the following best describes the relationship between temperature and $$\Delta S_{\text{surr}}$$?

$$\Delta S_{\text{surr}}$$ decreases as temperature increases.

Question 1

Which equation correctly describes the entropy change of the surroundings ($$\Delta S_{	ext{surr}}) $$for a reaction occurring at constant temperature?

Accepted Answer

$$\Delta S_{	ext{surr}} = -\Delta H_{	ext{sys}} / T$$

Question 2

A reaction has $$\Delta H_{	ext{rxn}} = +100\ 	ext{kJ}$$ and occurs at $$T = 300\ 	ext{K}. $$What is the value of $$\Delta S_{	ext{surr}} in$$ $$	ext{J}/	ext{K}$$?

Accepted Answer

$$\Delta S_{	ext{surr}} = -333.3\ 	ext{J}/	ext{K}$$

Question 3

Which statement best explains why freezing of water is spontaneous below $$0^\circ	ext{C}$$ but not above?

Accepted Answer

At low temperature, $$\Delta S_{	ext{surr}} is $$large and positive, dominating the negative $$\Delta S_{	ext{sys}}.$$

Question 4

For a reaction with $$\Delta H \u003c 0$$ and $$\Delta S \u003c 0$$, which temperature regime favors spontaneity?

Accepted Answer

Low temperature

Question 5

Given $$\Delta H = -150\ 	ext{kJ}$$ and $$\Delta S = -100\ 	ext{J}/	ext{K}$$, at what temperature does the reaction become nonspontaneous?

Accepted Answer

$$T = 150,000\ 	ext{J} / 100\ 	ext{J}/	ext{K} = 1500\ 	ext{K}$$

Question 6

Which of the following is the correct criterion for spontaneity in terms of Gibbs free energy?

Accepted Answer

$$\Delta G \u003c 0$$

Question 7

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

Accepted Answer

$$T \u003e 250\ 	ext{K}$$

Question 8

Which equation relates Gibbs free energy to entropy change of the universe?

Accepted Answer

$$\Delta G = -T\Delta S_{	ext{univ}}$$

Question 9

For the reaction $$2	ext{N}_2(g) + 	ext{O}_2(g) ightarrow 2	ext{N}_2	ext{O}(g)$$ with $$\Delta H_{	ext{rxn}} = +163.2\ 	ext{kJ}$$ and $$\Delta S_{	ext{sys}} = -109\ 	ext{J}/	ext{K} at$$ $$25^\circ	ext{C}$$, what is $$\Delta S_{	ext{surr}}$$?

Accepted Answer

$$-547.4\ 	ext{J}/	ext{K}$$

Question 10

Which physical meaning is associated with $$|\Delta G|$$ when $$\Delta G \u003c 0$$?

Accepted Answer

It is the maximum useful work the reaction can do.

Question 11

If a reaction is exothermic ($$\Delta H  0$$), what can be said about its spontaneity?

Accepted Answer

It is spontaneous at all temperatures.

Question 12

Which scenario describes a reaction that is spontaneous only at high temperatures?

Accepted Answer

$$\Delta H \u003e 0$$, $$\Delta S \u003e 0$$

Question 13

Electrolysis of water ($$2	ext{H}_2	ext{O}(l) ightarrow 2	ext{H}_2(g) + 	ext{O}_2(g)) is an $$example of which case regarding $$\Delta H$$ and $$\Delta S$$?

Accepted Answer

$$\Delta H \u003e 0$$, $$\Delta S \u003e 0$$

Question 14

Which of the following best describes the relationship between temperature and $$\Delta S_{	ext{surr}}$$?

Accepted Answer

$$\Delta S_{	ext{surr}}$$ decreases as temperature increases.

Question 15

If $$\Delta G = 0$$ for a chemical reaction, what does this indicate?

Accepted Answer

The reaction is at equilibrium.

Question 16

For a reaction with $$\Delta H \u003e 0$$ and $$\Delta S \u003c 0$$, what is the spontaneity at any temperature?

Accepted Answer

Never spontaneous

Question 17

Which formula is used to calculate the crossover temperature where $$\Delta G$$ changes sign?

Accepted Answer

$$T_{	ext{cross}} = \Delta H / \Delta S$$

Question 18

Which statement is true about the direction of spontaneous change in a chemical system?

Accepted Answer

Chemical systems always move toward lower Gibbs free energy.

Question 19

If $$Q \u003c K$$ for the reaction $$	ext{N}_2 + 3	ext{H}_2 ightleftharpoons 2	ext{NH}_3$$, what is the sign of $$\Delta G$$ and which direction is spontaneous?

Accepted Answer

$$\Delta G \u003c 0$$, forward direction is spontaneous

Entropy of the Surroundings & Gibbs Free Energy: Spontaneity and Temperature Dependence

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