Chemistry Chapter 12: Thermodynamics Study Guide

Consider the following reaction at 25 °C: 5 SO₃(g) + 2 NH₃(g) → 2 NO(g) + 5 SO₂(g) + 3 H₂O(g) If ∆H° = 42.4 kJ/mol and ∆S° = 562.3 J/mol•K, determine the standard free energy for the reaction at 25 °C.

-125 kJ/mol

Consider the reaction: ICl(g) + Cl₂(g) → ICl₃(s). The ∆G(f)° of ICl(g) is -5.5 kJ/mol and the ∆G(f)° of ICl₃(s) is -22.59 kJ/mol What is the ∆G° of the reaction, in kJ/mol?

-17.1 kJ/mol

Calculate ∆S° for C₃H₄(g) + 2 H₂(g) → C₃H₈(g).

-258.2 J/mol ･ K

Calculate ∆S° for NH₃(g) + HCl(g) → NH₄Cl(s).

-284.6 J/mol ･ K

Determine ∆G° for the phase change CO₂(g) → CO₂(aq) at 25°C.

-46.9 kJ/mol

What is the entropy change when 315 J of energy is reversibly transferred to a sample of water at 25°C?

1.06 J/K

Consider the reaction Cl₂(g) + Br₂(g) → 2 BrCl(g) at 25 °C. Using the information in the table, determine ∆S for this reaction.

11.6 J/mol･K

Determine ∆S° for 2 O₃(g) → 3 O₂(g).

137 J/mol ･ K

Determine ∆G° for the reaction 3 N₂(g) + 2 O₃(g) → 6 NO(g) at 223°C.

152 kJ/mol

What is S° for B in the reaction 3 A → 2 B if ∆S°(rxn) =-137.4 J/mol ･ K? [S° (A) = (205.0 J/mol ･K)]

238.8 J/mol ･ K

Determine ∆S for the phase change of 1.10 moles of water from solid to liquid at 0°C. (∆H = 6.01 kJ/mol)

24.2 J/K

What is ∆G° for the reaction CH₃OH(g) → CO(g) + 2 H₂(g) at 25°C?

24.8 kJ/mol

At what temperature, in °C, is a certain reaction at equilibrium if ∆H = +87.9 kJ/mol and ∆S = +170.2 J/mol ･ K?

242.9 °C

Consider the reaction Cl₂(g) + Br₂(g) → 2 BrCl(g) at 25 °C. The entropy change for the reaction is 11.6 J/mol･K. If the standard enthalpy change is 29.4 kJ/mol for the reaction, then what is the standard free energy for the reaction?

25.9 kJ/mol

At what temperature, in K, does X(l) → X(g) occur spontaneously?

349 K

Consider the following reaction at 25 °C: 5 SO₃(g) + 2 NH₃(g) → 2 NO(g) + 5 SO₂(g) + 3 H₂O(g) Given the information in the table, calculate ∆H° for the reaction.

42.4 kJ/mol

Consider the following reaction at 25 °C: 5 SO₃(g) + 2 NH₃(g) → 2 NO(g) + 5 SO₂(g) + 3 H₂O(g) Given the information in the table, calculate ∆S° for the reaction.

562.3 J/mol･K

What is the entropy when 1.20 moles of CCl₂F₂ vaporize at 25°C? [∆H(vap) = 17.2 kJ/mol at 25°C]

69.3 J/K

Consider the following reaction at 25 °C: 5 SO₃(g) + 2 NH₃(g) → 2 NO(g) + 5 SO₂(g) + 3 H₂O(g) If ∆H° = 42.4 kJ./mol and ∆S° = 562.3 J/mol•K, estimate the temperature at which this reaction would be at equilibrium assuming that enthalpy and entropy are independent of temperature.

75.4 K

What is ∆G° for the reaction CaO(s) + CO₂(g) → CaCO₃(s)?

886 kJ/mol

Which of the following is true about the total entropy of the universe? A) It is always increasing B) It is always decreasing C) It remains constant at a given T D) It always remains constant

A) It is always increasing

Which one of the following would have the smallest value of S°? A) Ne (g) B) O₂ (g) C) A mixture of Ne and O₂ D) CO₂ (g)

A) Ne (g)

Which of the following is true for a reaction when ∆G is a positive value?

A) The reverse of the reaction is spontaneous.

If a chemical reaction has a negative ∆H and a positive ∆S, then A) it will be spontaneous at all temperatures. B) it will be non-spontaneous at all temperatures. C) it will be spontaneous at high temperatures and non-spontaneous at low temperatures. D) it will be spontaneous at low temperatures and non-spontaneous at high temperatures. E) the absolute entropy of the reactants will be less than 0.

A) it will be spontaneous at all temperatures.

A reaction which is endothermic and has an overall increase in entropy is A) spontaneous only at high T B) spontaneous only at low T C) always spontaneous as written. D) always spontaneous in the reverse direction.

A) spontaneous only at high T

Predict how ∆G changes with increasing temperature for the reaction A(g) + B(g) → C(g).

A) ∆G becomes less negative and the reaction becomes less spontaneous.

Which of the following reactions would have the most positive ∆S° value? A) SO₂(g) + Na₂O(s) ⟶ Na₂SO₃(s) B) CO₂(s) ⟶ CO₂(g) C) Fe³⁺(aq) + SCN⁻(aq) ⟶ FeSCN²⁺(aq) D) N₂(g) + 3 H₂(g) ⟶ 2 NH₃(g) E) 2 NO(g) + Cl₂(g) ⟶ 2 NOCl(g)

B) CO₂(s) ⟶ CO₂(g)

Which one of the equations below is an exothermic reaction? A) CO₂ (g) → C (s) + O₂ (g) ∆H° = 394 kJ/mol B) CaO (s) + H₂O (l) → Ca(OH)₂ (aq) ∆H° = -64 kJ/mol C) C (s) + 2 F₂ (g) → CF₄ (g) ∆H° = 141.3 kJ/mol D) N₂ (g) + O₂ (g) → 2 NO (g) ∆H° = 180.6 kJ/mol

B) CaO (s) + H₂O (l) → Ca(OH)₂ (aq) ∆H° = -64 kJ/mol

Which of the following has the largest standard molar entropy?

B) H₂(g)

Which of the following processes has a negative ∆S? A) CaCO₃(s) → CaO(s) + CO₂(g) B) H₂O(g) → H₂O(s) C) CO₂(s) → CO₂(g) D) C₆H₁₂O₆(s) → C₆H₁₂O₆(aq) E) ∆S cannot be negative

B) H₂O(g) → H₂O(s)

Which of the following is true for a process where ∆S(universe) < 0 at 298 K? A) It is exothermic B) It is nonspontaneous. C) It is product-favored. D) It is spontaneous. E) It is endothermic.

B) It is nonspontaneous.

Consider the reaction Cl₂(g) + Br₂(g) → 2 BrCl(g) at 25 °C. The change in the free energy under standard conditions is 25.9 kJ/mol. Is this reaction spontaneous as written under standard conditions? A) Yes, because ∆G° > 0. B) No, because ∆G° > 0.

B) No, because ∆G° > 0.

If ∆H > 0 and ∆S < 0, a reaction will be: A) Spontaneous B) Nonspontaneous C) At equilibrium D) Not enough info

B) Nonspontaneous

Which of the following best describes the third law of thermodynamics? A) ∆U(univ) = ∆U(sys) + ∆U(surr) B) S° = 0 for perfect Li(s) at 0 K C) ∆S(univ) > 0 (spontaneous process) D) ∆S = ∆H(rev)/T at constant T E) ∆G = ∆H - T∆S

B) S° = 0 for perfect Li(s) at 0 K

Consider the reaction Cl₂(g) + Br₂(g) → 2 BrCl(g) at 25 °C. Which of the following best explains why the change in entropy is so small? A) All of the components in the chemical equation are gases. B) There are the same moles of gas on both sides of the reaction. C) The temperature of the reaction does not change.

B) There are the same moles of gas on both sides of the reaction.

If the Gibbs free energy for an equilibrium is a large, negative number, the equilibrium constant is expected to be _____ A) a large, negative value B) a large, positive value C) a small, negative value D) a small, positive value E) Zero

B) a large, positive value

If a chemical reaction has a positive ∆H and a negative ∆S, then A) it will be spontaneous at all temperatures. B) it will be non-spontaneous at all temperatures. C) it will be spontaneous at high temperatures and non-spontaneous at low temperatures. D) it will be spontaneous at low temperatures and non-spontaneous at high temperatures. E) the absolute entropy of the products will be less than 0.

B) it will be non-spontaneous at all temperatures.

Which set of results applies to a reaction that is not spontaneous at 273 K but is spontaneous at 400 K? A) ∆H < 0 and ∆S > 0 B) ∆H > 0 and ∆S > 0 C) ∆H < 0 and ∆S < 0 D) ∆H > 0 and ∆S < 0 E) None of these

B) ∆H > 0 and ∆S > 0

Which of the following is true for all reversible endothermic processes? A) ∆H(sys) > 0, ∆S(surr) > 0 B) ∆H(sys) > 0, ∆S(surr) < 0 C) ∆H(sys) < 0, ∆S(surr) > 0 D) ∆H(sys) < 0, ∆S(surr) < 0 E) ∆H(sys) > 0, ∆S(surr) = 0

B) ∆H(sys) > 0, ∆S(surr) < 0

Which of the following best describes the reaction? 2 H₂S(g) + 3 O₂(g) → 2 H₂O(g) + 2 SO₂(g)

B) ∆S° has a small negative value.

Which of the following is true for a system at equilibrium? A) ∆S°(sys) = ∆S°(surr) B) ∆S°(sys) = -∆S°(surr) C) ∆S°(sys) = ∆S°(surr) = 0 D) ∆S°(sys) = ∆S°(univ) E) ∆S°(surr) = ∆S°(univ)

B) ∆S°(sys) = -∆S°(surr)

Which one of the following reactions would produce the largest amount of heat per mole of hydrogen? A) C (s) + 2 H₂ (g) → CH₄ (g) ∆H° = -74.9 kJ/mol B) N₂O (g) + 3 H₂ (g) → N₂H₄ (g) + H₂O (l) ∆H° = -316.8 kJ/mol C) 2 H₂ (g) + O₂ (g) → 2 H₂O (l) ∆H° = -571.6 kJ/mol D) N₂ (g) + 3 H₂ (g) → 2 NH₃ (g) ∆H° = -91.8 kJ/mol

C) 2 H₂ (g) + O₂ (g) → 2 H₂O (l) ∆H° = -571.6 kJ/mol

Which one of the following would have the largest molar entropy? A) Al (s) B) S (s) C) Al₂S₃ (s)

C) Al₂S₃ (s)

What must be true of a spontaneous process? A) Enthalpy must increase. B) There will be a flow of heat. C) Entropy of the universe increases. D) Entropy of the system increases. E) Entropy of the surroundings increases.

C) Entropy of the universe increases.

Which of the following is true about a spontaneous process? A) It releases energy. B) It will occur quickly. C) It will continue on its own once begun. D) It is never endothermic.

C) It will continue on its own once begun.

Which of the following reactions results in an increase in the entropy of the system? A) CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g) B) BaO(s) + CO₂(g) → BaCO₃(s) C) NH₄Cl(s) → HCl(g) + NH₃(g) D) 2HCl(g) + F₂(g) → 2HF(g) + Cl₂(g) E) 4Co(s) + 3O₂(g) → 2Co₂O₃(s)

C) NH₄Cl(s) → HCl(g) + NH₃(g)

For a reaction for which ∆H = -64.2 kJ/mol and ∆S = 285 J/mol･K, which of the following statements is true? A) The reaction is spontaneous only above 225 K. B) The reaction is spontaneous below 225 K. C) The reaction will never reach equilibrium. D) The reaction is always at equilibrium.

C) The reaction will never reach equilibrium.

Consider the following reaction at 25 °C: 5 SO₃(g) + 2 NH₃(g) → 2 NO(g) + 5 SO₂(g) + 3 H₂O(g) If ∆G° = -125 kJ/mol, ∆H° = 42.4 kJ/mol and ∆S° = 562.3 J/mol•K, is this reaction spontaneous as written under standard conditions? A) No, it is not spontaneous because enthalpy and entropy are positive. B) No, it is not spontaneous because the free energy is negative. C) Yes, it is spontaneous because the free energy is negative. D) Yes, it is spontaneous because the entropy is positive.

C) Yes, it is spontaneous because the free energy is negative.

A reaction which is exothermic and has an overall increase in entropy is A) spontaneous only at high T B) spontaneous only at low T C) always spontaneous D) spontaneous in the reverse direction.

C) always spontaneous

If a chemical reaction has a positive ∆H and a positive ∆S, then A) it will be spontaneous at all temperatures. B) it will be non-spontaneous at all temperatures. C) it will be spontaneous at high temperatures and non-spontaneous at low temperatures. D) it will be spontaneous at low temperatures and non-spontaneous at high temperatures. E) the absolute entropy of the products will be less than 0.

C) it will be spontaneous at high temperatures and non-spontaneous at low temperatures.

Which of the following does the change in the free energy of a reaction predict? A) the work done B) the speed C) the spontaneity D) the final temperature E) the heat released

C) the spontaneity

Which of the following is always true for an equilibrium? A) ∆S = 0 B) ∆H = 0 C) ∆G = 0 D) T = 298 K E) K = 0

C) ∆G = 0

Which set of results applies to a reaction that is spontaneous at 250 K but is nonspontaneous at 350 K? A) ∆H < 0 and ∆S > 0 B) ∆H > 0 and ∆S > 0 C) ∆H < 0 and ∆S < 0 D) ∆H > 0 and ∆S < 0 E) None of these

C) ∆H < 0 and ∆S < 0

In the statement 'all spontaneous changes result in an increase in entropy', the entropy change is _____.

C) ∆S(univ)

How many of the following processes are nonspontaneous? climbing stairs dissolving salt in water converting table salt to its elements 2 H₂O(l) → 2 H₂(g) + O₂(g)

D) 3

Which of the following phase changes is not spontaneous at room temperature? Assume only the first phase is initially present.

D) H₂O(g) → H₂O(s)

What will the sign on ∆S be for the following reaction and why? 2 Mg (s) + O₂ (g) → 2 MgO (s) A) Positive, because there is a solid as a product. B) Positive, because there are more moles of reactant than product. C) Positive, because it is a synthesis reaction. D) Negative, because there are more moles of gas on the reactant side than the product side. E) Negative, because there are more moles of reactant than product.

D) Negative, because there are more moles of gas on the reactant side than the product side.

If ∆H < 0 and ∆S < 0, a reaction will be: A) Spontaneous B) Nonspontaneous C) At equilibrium D) Not enough information

D) Not enough information

Which is true for the endothermic reaction 2 SO₃(g) → 2 SO₂(g) + O₂(g)? A) Spontaneous at all T B) Spontaneous at low T C) Non-spontaneous at any T D) Spontaneous at high T

D) Spontaneous at high T

Which law states that the entropy of a perfect crystalline substance is zero at the absolute zero of temperature? A) Zeroth law of thermodynamics B) First law of thermodynamics C) Second law of thermodynamics D) Third law of thermodynamics E) Law of conservation of energy

D) Third law of thermodynamics

The second law of thermodynamics states that _____ A) no engine can be 100% efficient. B) transferring energy from a cold to a hot bath requires work. C) the entropy of the universe increases with a spontaneous process. D) all of these are true.

D) all of these are true.

If a chemical reaction has a negative ∆H and a negative ∆S, then A) it will be spontaneous at all temperatures. B) it will be non-spontaneous at all temperatures. C) it will be spontaneous at high temperatures and non-spontaneous at low temperatures. D) it will be spontaneous at low temperatures and non-spontaneous at high temperatures. E) the absolute entropy of the products will be less than 0.

D) it will be spontaneous at low temperatures and non-spontaneous at high temperatures.

A reaction will be spontaneous at all temperatures if _____ A) ∆H and ∆S are positive B) ∆H and ∆S are negative C) ∆H is positive and ∆S is negative D) ∆H is negative and ∆S is positive

D) ∆H is negative and ∆S is positive

Which of the following are spontaneous processes? 1. Ice melting at 273 K (assume only ice is initially present). 2. Heat flowing from a hot object to a cold object. 3. An iron bar rusting.

E) 1, 2, and 3

Which of the following is not true about a spontaneous process? A) A spontaneous process is one that continues on its own once begun. B) Spontaneous processes occur naturally. C) A nonspontaneous process does not occur unless some external action is applied. D) A nonspontaneous process does not mean it cannot ever occur under any conditions. E) A spontaneous process is also spontaneous in the reverse direction.

E) A spontaneous process is also spontaneous in the reverse direction.

Which of the following processes is spontaneous? A) Heat coming out of an open oven. B) A puddle evaporating in the sun. C) A car rusting. D) Water turning into ice in a freezer. E) All of the above

E) All of the above

Which of the following describes the entropy change in the given reaction? 2 Cl₂O₇(g) → 2 Cl₂(g) + 7 O₂(g) A) The entropy change is negative because a larger molecule (Cl₂O₇) is converted into two smaller molecules (Cl₂ and O₂). B) The entropy change is zero because the reactants and products are all gases. C) The entropy change cannot be determined because the temperature is not specified. D) The entropy change is negative because there are more moles of products than reactants. E) The entropy change is positive because there are more moles of products than reactants.

E) The entropy change is positive because there are more moles of products than reactants.

Cl₂ is a stable diatomic molecule. It can be decomposed to form two Cl atoms as shown below. Cl₂ → 2Cl(g) Predict the change in free energy (∆G) of this reaction. A) ∆G is (-); endergonic B) ∆G is (+); endergonic C) ∆G is (-); exergonic D) ∆G is (+); exergonic E) ∆G is dependent upon the temperature of the reaction

E) ∆G is dependent upon the temperature of the reaction

Which of the following sets of conditions is true for an exothermic reaction that is spontaneous at all temperatures? A) ∆H < 0, ∆S < 0, ∆G < 0 B) ∆H > 0, ∆S < 0, ∆G < 0 C) ∆H < 0 , ∆S < 0, ∆G > 0 D) ∆H > 0, ∆S < 0, ∆G < 0 E) ∆H < 0, ∆S > 0, ∆G < 0

E) ∆H < 0, ∆S > 0, ∆G < 0

Which of the following guarantees a reaction will be spontaneous? A) ∆H > 0 B) ∆S(sys) > 0 C) ∆H < 0 D) ∆S(surr) > ∆S(sys) E) ∆S > ∆H/T

E) ∆S > ∆H/T

Which of the following would have zero entropy? I. O₂(g) at 273 K II. amorphous SiCN(s) at 1 K III. KBr(s, perfect crystal) at 10 K IV. Li(s, perfect crystal) at 0 K

IV only