Homework answers / question archive / Chapter 17: Entropy, Free Energy, and Equilibrium 1)Which of these species would you expect to have the lowest standard entropy (S°)?                   A)  CH4(g)    B)  HF(g)    C)  NH3(g)    D)  H2O(g)     Which of these species would you expect to have the highest standard entropy (S°)?   A)  CH4(g)    B)  C2H2(g)    C)  C2H4(g)    D)  C2H6(g)    E)  C3H8(g)   Ans:  E       Which of these species would you expect to have the lowest standard entropy (S°)?                      A)  Br2(l)    B)  Cl2(g)    C)  F2(g)    D)  H2(g)    E)  I2(s)     Which of these species has the highest entropy (S°) at 25°C?   A)  CH3OH(l)    B)  CO(g)    C)  MgCO3(s)    D)  H2O(l)    E)  Ni(s)   Ans:  B       Which of these species has the highest entropy (S°) at 25°C?                     A)  CO(g)    B)  CH4(g)    C)  NaCl(s)    D)  H2O(l)    E)  Fe(s)     Arrange these compounds in order of increasing standard molar entropy at 25°C:                          C3H8(g), C2H4(g), ZnS(s), and H2O(l)

Chapter 17: Entropy, Free Energy, and Equilibrium 1)Which of these species would you expect to have the lowest standard entropy (S°)?                   A)  CH4(g)    B)  HF(g)    C)  NH3(g)    D)  H2O(g)     Which of these species would you expect to have the highest standard entropy (S°)?   A)  CH4(g)    B)  C2H2(g)    C)  C2H4(g)    D)  C2H6(g)    E)  C3H8(g)   Ans:  E       Which of these species would you expect to have the lowest standard entropy (S°)?                      A)  Br2(l)    B)  Cl2(g)    C)  F2(g)    D)  H2(g)    E)  I2(s)     Which of these species has the highest entropy (S°) at 25°C?   A)  CH3OH(l)    B)  CO(g)    C)  MgCO3(s)    D)  H2O(l)    E)  Ni(s)   Ans:  B       Which of these species has the highest entropy (S°) at 25°C?                     A)  CO(g)    B)  CH4(g)    C)  NaCl(s)    D)  H2O(l)    E)  Fe(s)     Arrange these compounds in order of increasing standard molar entropy at 25°C:                          C3H8(g), C2H4(g), ZnS(s), and H2O(l)

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Chapter 17: Entropy, Free Energy, and Equilibrium

1)Which of these species would you expect to have the lowest standard entropy (S°)?

                  A)  CH₄(g)    B)  HF(g)    C)  NH₃(g)    D)  H₂O(g)

 

 

1. Which of these species would you expect to have the highest standard entropy (S°)?

  A)  CH₄(g)    B)  C₂H₂(g)    C)  C₂H₄(g)    D)  C₂H₆(g)    E)  C₃H₈(g)   Ans:  E    

 

2. Which of these species would you expect to have the lowest standard entropy (S°)?

                     A)  Br₂(l)    B)  Cl₂(g)    C)  F₂(g)    D)  H₂(g)    E)  I₂(s)

 

 

3. Which of these species has the highest entropy (S°) at 25°C?

  A)  CH₃OH(l)    B)  CO(g)    C)  MgCO₃(s)    D)  H₂O(l)    E)  Ni(s)   Ans:  B    

 

4. Which of these species has the highest entropy (S°) at 25°C?

                    A)  CO(g)    B)  CH₄(g)    C)  NaCl(s)    D)  H₂O(l)    E)  Fe(s)

 

 

5. Arrange these compounds in order of increasing standard molar entropy at 25°C:

                         C₃H₈(g), C₂H₄(g), ZnS(s), and H₂O(l).

1. 1. 1. ZnS(s) < H₂O(l) < C₃H₈(g) < C₂H₄(g)
      2. C₂H₄(g) < H₂O(l) < C₃H₈(g) < NaCl(s)
      3. ZnS(s) < C₃H₈(g) < C₂H₄(g) < H₂O(l)         D)        C₃H₈(g) < C₂H₄(g) < H₂O(l) < ZnS(s)

             E)      ZnS(s) < H₂O(l) < C₂H₄(g) < C₃H₈(g)

 

 

6. Arrange the following substances in the order of increasing entropy at 25°C.                         HF(g), NaF(s), SiF₄(g), SiH₄(g), Al(s)             lowest → highest

            A)        SiF₄(g) < SiH₄(g) < NaF(s) < HF(g) < Al(s)  B)        HF(g) < Al(s) < NaF(s) < SiF₄(g) < SiH₄(g)              C)        Al(s) < NaF(s) < HF(g) < SiH₄(g) < SiF₄(g)       D)        Al(s) < HF(g) < NaF(s) < SiF₄(g) < SiH₄(g)

             E)      NaF(s) < Al(s) < HF(g) < SiF₄(g) < SiH₄(g)

 

 

7. Which one of the following reactions would you expect to have the lowest ?S°?
   1. 1. CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)
      2. C₂H₂(g) + ⁵/₂O₂(g) → 2CO₂(g) + H₂O(g)    C)         C₂H₄(g) + O₂(g) → 2CO₂(g) + 2H₂O(g)

            D)      C₂H₆(g) + ⁷/₂O₂(g) → 2CO₂(g) + 3H₂O(g)

 

 

8. Which one of the following reactions would you expect to have highest ?S°?
   1. 1. CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)
      2. C₂H₂(g) + ⁵/₂O₂(g) → 2CO₂(g) + H₂O(g)
      3. C₂H₄(g) + 3O₂(g) → 2CO₂(g) + 2H₂O(g)
      4. C₂H₆(g) + ⁷/₂O₂(g) → 2CO₂(g) + 3H₂O(g)

 

 

9. Which response includes all the following processes that are accompanied by an increase in entropy?
   1. 1. 1. 1. 2SO₂(g) + O₂(g) → SO₃(g)
            2. H₂O(l) → H₂O(s)
            3. Br₂(l) → Br₂(g)
            4. H₂O₂(l) → H₂O(l) + ¹/₂O₂(g)

                    A)  1, 2, 3, 4    B)  1, 2    C)  2, 3, 4    D)  3, 4    E)  1, 4

 

 

10. Which response includes all of the following processes that are accompanied by an increase in entropy?
    1. 1. 1. 1. I₂(s) → I₂(g)
             2. 2I(g) → I₂(g)
             3. 2NH₃(g) → N₂(g) + 3H₂(g)
             4. Mg²⁺(aq) + 2OH^–(aq) → Mg(OH)₂(s)

                    A)  1, 2    B)  1, 3    C)  3, 4    D)  3    E)  2, 4

 

 

11. Which response includes all of the following processes that are accompanied by an increase of entropy?

             

 

 

                  A)  I and III    B)  II and III    C)  I, II and III    D)  II only    E)  III only

                                               Ans:  A    

 

12. Without reference to a table, arrange these reactions according to increasing ?S.
    1. 1. 1. CH₄(g) + H₂O(g) → CO(g) + 3H₂(g)
          2. C(s) + O₂(g) → CO₂(g)
          3. H₂O₂(l) → H₂O(l) + ¹/₂O₂(g)

                    A)  1 < 3 < 2    B)  2 < 3 < 1    C)  2 < 1 < 3    D)  3 < 2 < 1    E)  3 < 1 < 2

 

 

13. Arrange these reactions according to increasing ?S.
    1. 1. 1. H₂O(g) → H₂O(l)
          2. 2NO(g) → N₂(g) + O₂(g)
          3. MgCO₃(s) → MgO(s) + CO₂(g)

                    A)  1 < 2 < 3    B)  2 < 3 < 1    C)  3 < 2 < 1    D)  2 < 1 < 3    E)  1 < 3 < 2

                                               Ans:  A    

 

14. Which of the following processes would be accompanied by an increase in entropy?
    1. 1. H₂O(g) → H₂O(s)    D)        H₂O(s) → H₂O(g)
       2. H₂O(l) → H₂O(s)     E)        H₂O(l, 50°C) → H₂O(l, 25°C)
       3. H₂O(g) → H₂O(l)                 

 

 

15. Which of the following processes would be accompanied by a decrease in entropy?
    1. 1. H₂O(s) → H₂O(g)    D)        H₂O(g) → H₂O(s)
       2. H₂O(l) → H₂O(g)    E)        H₂O(l, 50°C) → H₂O(l, 75°C)
       3. H₂O(s) → H₂O(l)                  

 

 

16. Which of the following is expected to have zero entropy?
    1. 1. N₂(g) at 273 K
       2. SiO₂(s, amorphous) at 0 K
       3. NaCl(s) perfectly ordered crystal at 25 K
       4. Na(s) perfectly ordered crystal at 0 K

                  A)  I and IV    B)  III and IV    C)  I and II    D)  I, II, and III    E)  IV only

 

 

17. Aluminum forms a layer of aluminum oxide when exposed to air which protects the bulk metal from further corrosion.                       4Al(s) + 3O₂(g) → 2Al₂O₃(s)

             Using the thermodynamic data provided below, calculate ?S° for this reaction.                 

	S°(J/K·mol)
Al(s)	28.3
O2(g)	205.0
Al2O3(s)	50.99

 

1. 1. 1. 182.3 J/K·mol          D)        –626.2 J/K·mol
      2. 131.5 J/K·mol          E)        –802.9 J/K·mol
      3. –182.3 J/K·mol                     

 

 

18. Sulfur can be separated from lead in the mineral galena, PbS(s), by “roasting” the ore in the presence of oxygen as shown in the following reaction:

                          2PbS(s) + 3O₂(g) → 2PbO(s) + 2SO₂(g)

             Calculate ?S° for this reaction using the thermodynamic data provided below.                  

	S°(J/K·mol)
PbS(s)	91.2
O2(g)	205.0
PbO(s)	69.45
SO2(g)	248.5

 

 A) –410 J/K·mol D) 21.8 J/K·mol  B) –161.5 J/K·mol E) 43.5 J/K·mol

            C)      –47.7 J/K·mol                                                  

 

 

19. Determine ?S° for the reaction SO₃(g) + H₂O(l) → H₂SO₄(l).

		S°(J/K·mol)
	SO3	256.2
	H2O	69.9
	H2SO4	156.9
A)	169.2 J/K·mol	D)	–29.4 J/K·mol
B)	1343.2 J/K·mol	E)	29.4 J/K·mol
C)	–169.2 J/K·mol

 

 

20. Calculate ?S° for the reaction SO₂(s) + NO₂(g) → SO₃(g) + NO(g).

		S°(J/K·mol)
	SO2(g)	248.5
	SO3(g)	256.2
	NO(g)	210.6
	NO2(g)	240.5
A)	53.6 J/K·mol	D)	474.8 J/K·mol
B)	–53.6 J/K·mol	E)	–474.8 J/K·mol
C)	–22.2 J/K·mol

 

 

21. Calculate ?S° at 25°C for the reduction of PbO(s), 2PbO(s) + C(s) → 2Pb(s) + CO₂(g) given these absolute entropies:

		S°  (J/K·mol)
	PbO(s)	69.45
	C(s)	5.7
	Pb(s)	64.89
	CO2(g)	213.6
A)	+198.8 J/K·mol	D)	–203.3 J/K·mol
B)	+488.0 J/K·mol	E)	+203.3 J/K·mol
C)	+353.6 J/K·mol

 

 

22. Which of the following is consistent with a spontaneous process in the forward direction?
    1. 1. ?S_univ > 0, ?G < 0, T?S_univ > 0     D) ?S_univ < 0, ?G < 0, T?S_univ < 0
       2. ?S_univ < 0, ?G > 0, T?S_univ < 0     E) ?S_univ > 0, ?G > 0, T?S_univ > 0
       3. ?S_univ > 0, ?G < 0, T?S_univ < 0                  

 

 

23. Which of the following is consistent with a nonspontaneous process in the forward direction?
    1. 1. ?S_univ > 0, ?G < 0, T?S_univ > 0     D) ?S_univ < 0, ?G < 0, T?S_univ < 0
       2. ?S_univ < 0, ?G > 0, T?S_univ < 0     E) ?S_univ > 0, ?G > 0, T?S_univ > 0
       3. ?S_univ > 0, ?G < 0, T?S_univ < 0                  

 

 

24. HI has a normal boiling point of –35.4°C, and its ?H_vap is 21.16 kJ/mol.  Calculate the molar entropy of vaporization (?S_vap).
    1. 1. 598 J/K·mol             D)        0.068 J/K·mol
       2. 68.6 J/K·mol            E)        89.0 J/K·mol
       3. 75.2 J/K·mol                         

 

 

25. With respect to the system only, a reaction with ?H > 0 and ?S < 0 is predicted to be:
    1. 1. Spontaneous at all temperatures
       2. Spontaneous at high temperatures only
       3. Spontaneous at low temperatures only
       4. Nonspontaneous at all temperatures

 

 

26. With respect to the system only, a reaction with ?H < 0 and ?S > 0 is predicted to be:
    1. 1. Spontaneous at all temperatures
       2. Spontaneous at high temperatures only
       3. Spontaneous at low temperatures only
       4. Nonspontaneous at all temperatures

 

 

27. Which of the following is consistent with a spontaneous endothermic reaction?
    1. 1. ?H > 0, ?S < 0, ?G < 0    D) ?H < 0, ?S > 0, ?G > 0
       2. ?H > 0, ?S > 0, ?G < 0    E) ?H > 0, ?S < 0, ?G > 0
       3. ?H < 0, ?S < 0, ?G < 0                 

 

 

28. Which of the following is consistent with an exothermic reaction that is spontaneous at all temperatures?    
    1. 1. ?H > 0, ?S < 0, ?G < 0    D) ?H < 0, ?S > 0, ?G < 0
       2. ?H > 0, ?S > 0, ?G < 0    E) ?H > 0, ?S < 0, ?G > 0
       3. ?H < 0, ?S < 0, ?G < 0                 

 

 

29. Which of the following is consistent with an exothermic reaction that is nonspontaneous at high temperatures? 
    1. 1. ?H > 0, ?S < 0, ?G < 0    D) ?H < 0, ?S > 0, ?G > 0
       2. ?H > 0, ?S > 0, ?G < 0    E) ?H < 0, ?S < 0, ?G > 0
       3. ?H < 0, ?S > 0, ?G < 0                             

 

 

30. Aluminum forms a layer of aluminum oxide when exposed to air which protects the bulk metal from further corrosion.

                          4Al(s) + 3O₂(g) → 2Al₂O₃(s)

            Calculate ?G° for this reaction, given that ?G°_f of aluminum oxide is –1576.4 kJ/mol.

1. 1. 1. –3152.8 kJ/mol        D)        1576.4 kJ/mol
      2. –1576.4 kJ/mol        E)        3152.8 kJ/mol
      3. –788.2 kJ/mol                       

 

 

31. Calculate ?G° for the reaction 3NO₂(g) + H₂O(l) → 2HNO₃(l) + NO(g).

		?G°f  (kJ/mol)
	H2O(l)	–237.2
	HNO3(l)	–79.9
	NO(g)	86.7
	NO2(g)	51.8
A)	8.7 kJ/mol	D)	–192 kJ/mol
B)	192 kJ/mol	E)	–155 kJ/mol
C)	–414 kJ/mol

 

 

32. Ozone (O₃) in the atmosphere can reaction with nitric oxide (NO):

                          O₃(g) + NO(g) → NO₂(g) + O₂(g).

            Calculate the ?G° for this reaction at 25°C.  (?H° = –199 kJ/mol, ?S° = –4.1 J/K·mol)

1. 1. 1. 1020 kJ/mol             D)        –1.42 × 10³ kJ/mol
      2. –1.22 × 10³ kJ/mol E)        –198 kJ/mol
      3. 2.00 × 10³ kJ/mol                 

 

 

33. Sodium carbonate can be made by heating sodium bicarbonate:

                         2NaHCO₃(s) → Na₂CO₃(s) + CO₂(g) + H₂O(g)

             Given that ?H° = 128.9 kJ/mol and ?G° = 33.1 kJ/mol at 25°C, above what minimum temperature will the reaction become spontaneous under standard state conditions?

                    A)  0.4 K    B)  3.9 K    C)  321 K    D)  401 K    E)  525 K

 

 

34. The element oxygen was prepared by Joseph Priestley in 1774 by heating mercury(II) oxide:

                          HgO(s) → Hg(l) + ¹/₂O₂(g),  ?H° = 90.84 kJ/mol.

             Estimate the temperature at which this reaction will become spontaneous under standard state conditions.

                          S°(Hg) = 76.02 J/K·mol

                         S°(O₂) = 205.0 J/K·mol

                         S°(HgO) = 70.29 J/K·mol

                    A)  108 K    B)  430 K    C)  620 K    D)  775 K    E)  840 K

 

 

35. For the reaction H₂(g) + S(s) → H₂S(g), ?H° = –20.2 kJ/mol and ?S° = +43.1 J/K·mol.

Which of these statements is true?

1. 1. 1. The reaction is only spontaneous at low temperatures.
      2. The reaction is spontaneous at all temperatures.     C) ?G° becomes less favorable as temperature increases.

1. 1. 4. The reaction is spontaneous only at high temperatures.
      5. The reaction is at equilibrium at 25°C under standard conditions.

 

 

36. The normal freezing point of ammonia is –78°C.  Predict the signs of ?H, ?S, and ?G for ammonia when it freezes at –80°C and 1 atm:  NH₃(l) → NH₃(s)

                        

 

 

                    A)  A    B)  B    C)  C    D)  D    E)  E

 

 

37. The normal melting point sulfur is 113 °C. If a sample of solid sulfur is at 95 °C, Predict the signs of ?H, ?S, and ?G for the melting process at this temperature.
    1. 1. ?H > 0, ?S > 0, ?G < 0    D) ?H < 0, ?S > 0, ?G > 0
       2. ?H > 0, ?S > 0, ?G > 0    E) ?H < 0, ?S < 0, ?G > 0
       3. ?H > 0, ?S < 0, ?G < 0                             

 

 

38. The normal boiling point of acetic acid is 118.1°C. If a sample of the acetic acid is at 125.2°C, Predict the signs of ?H, ?S, and ?G for the boiling process at this temperature.
    1. 1. ?H > 0, ?S > 0, ?G < 0    D) ?H < 0, ?S > 0, ?G > 0
       2. ?H > 0, ?S > 0, ?G > 0    E) ?H < 0, ?S < 0, ?G > 0
       3. ?H > 0, ?S < 0, ?G < 0                 

 

 

39. Hydrogen peroxide (H₂O₂) decomposes according to the equation

                          H₂O₂(l) → H₂O(l) + ¹/₂O₂(g).

             Calculate K_p for this reaction at 25°C.  (?H° = –98.2 kJ/mol, ?S° =  70.1 J/K·mol)

  A)  1.3 × 10^–21    B)  20.9    C)  3.46 × 10¹⁷    D)  7.5 × 10²⁰    E)  8.6 × 10⁴   Ans:  D      

 

40. At 1500°C the equilibrium constant for the reaction CO(g) + 2H₂(g)

    

    CH₃OH(g) has the value K_p = 1.4 × 10^–7.  Calculate ?G° for this reaction at 1500°C.
    1. 1. 105 kJ/mol   D)        –105 kJ/mol
       2. 1.07 kJ/mol E)        233 kJ/mol
       3. –233 kJ/mol                          

 

 

41. Calculate K_p at 298 K for the reaction SO₂(g) + NO₂(g)

    

     SO₃(g) + NO(g).

	?G°f
SO2(g)	–300.4 kJ/mol
SO3(g)	–370.4 kJ/mol
NO(g)	86.7 kJ/mol
NO2(g)	51.8 kJ/mol

  A)  6.99 × 10^–7    B)  5.71 × 10^–8    C)  14.2    D)  475    E)  1.42 × 10⁶   Ans:  E      

 

42. The equilibrium constant at 427°C for the reaction N₂(g) + 3H₂(g)

    

    2NH₃(g) is K_p =

9.4 × 10^–5.  Calculate the value of ?G° for the reaction under these conditions.

             A)  –33 kJ/mol    B)  –54 kJ/mol    C)  54 kJ/mol    D)  33 kJ/mol    E)  1.3 J/mol

 

 

43. Determine the equilibrium constant K_p at 25°C for the reaction N₂(g) + 3H₂(g)

    

    2NH₃(g)

                         [?G°_f (NH₃(g)) = –16.6 kJ/mol].

  A)  1.52 × 10^–6    B)  6.60 × 10⁵    C)  8.28 × 10^–2    D)  2.60    E)  13.4   Ans:  B      

 

44. Calculate the equilibrium constant for the decomposition of water                 2H₂O(l)

    

    2H₂(g) + O₂(g)       at 25°C, given that ?G°_f (H₂O(l)) = –237.2 kJ/mol.

  A)  0.83    B)  6.3 × 10^–84    C)  2.5 × 10^–42    D)  1.6 × 10⁸³    E)  4.7 × 10⁵   Ans:  B      

 

45. Nitrosyl chloride (NOCl) decomposes at elevated temperatures according to the equation

             2NOCl(g)

2NO(g) + Cl₂(g).  Calculate K_p for this reaction at 227°C. (?H° = 81.2 kJ/mol, ?S° = 128 J/K·mol)

 

  A)  1.59 × 10^–2    B)  2.10 × 10^–7    C)  62.8    D)  4.90 × 10⁶    E)  3.20 × 10⁹   Ans:  A      

 

46. The equilibrium constant for the reaction AgBr(s)

    

    Ag⁺(aq) + Br^– (aq) is the solubility product constant, K_sp = 7.7 × 10^–13 at 25°C.  Calculate ?G for the reaction when [Ag⁺] = 1.0 × 10^–2 M and [Br^–] = 1.0 × 10^–3 M.  Is the reaction spontaneous or nonspontaneous at these concentrations?
    1. 1. ?G = 69.1 kJ/mol, nonspontaneous            D) ?G = 40.6 kJ/mol, nonspontaneous
       2. ?G = –69.1 kJ/mol, spontaneous    E) ?G = –97.5 kJ/mol, nonspontaneous
       3. ?G = 97.5 kJ/mol, spontaneous                   

Category:  Difficult     Section:  17.6

 

47. For the reaction 2C(graphite) + H₂(g) → C₂H₂(g), ?G°= +209.2 kJ/mol at 25°C.  If P(H₂) = 100. atm, and P(C₂H₂) = 0.10 atm, calculate ?G for this reaction.
    1. 1. +207.8 kJ/mol          D)        +17.3 kJ/mol
       2. +226.3 kJ/mol          E)        –16.9 kJ/mol
       3. +192.1 kJ/mol                       

 

 

48. For the reaction 2 SO₂(g) + O₂(g) → 2 SO₃(g), if initially P(SO₂) = 1.2 atm, P(O₂) = 1.8 atm, and P(SO₃) = 2.1 atm, calculate ?G for this reaction at 25°C. The following data is valid at 25°C:

	?Gf° (kJ/mol)
SO2	–300.4
SO3	–370.4

 

1. 1. 1. –140.0 kJ/mol          D)        1,174.7 kJ/mol
      2. –137.6 kJ/mol          E)        –141.3 kJ/mol
      3. –138.7 kJ/mol                       

 

 

49. For the reaction 2NO(g) + O₂(g) → 2NO₂(g) if initially P(NO) = 1.5 atm, P(O₂) = 1.4 atm, and P(NO₂) = 2.0 atm, calculate ?G for this reaction at 25°C. The following data is valid at 25°C:

	?Gf° (kJ/mol)
NO	86.7
NO2	51.8

 

1. 1. 1. –69.9 kJ/mol            D)        –79.9 kJ/mol
      2. –69.2 kJ/mol            E)        –35.0 kJ/mol
      3. 522.1 kJ/mol                         

 

 

50. Determine the equilibrium constant (K_p) at 25°C for the reaction

                                 CO(g) + H₂O(g)

CO₂(g) + H₂(g)              ^?G° = –28.5 kJ/mol.

 

 

  A)  2.9 × 10^–60    B)  1.0 × 10^–4    C)  1.2    D)  1.0 × 10⁵    E)  3.4 × 10⁵⁹   Ans:  D      

 

51. K_w for the auto-ionization of water, H₂O(l) → H⁺(aq) + OH^– (aq), is 1.0 × 10^–14.  What are the signs (+/–) of ?S° and ?H° for the reaction at 25°C?
    1. 1. ?S° = (+) and ?H° = (+)    C) ?S° = (–) and ?H° = (+)
       2. ?S° = (+) and ?H° = (–)    D) ?S° = (–) and ?H° = (–)

 

 

52. Which of the following is consistent with a reaction at equilibrium?
    1. 1. ?G = 0, Q = K        D) ?G < 0, Q = K
       2. ?G° = 0, Q > K      E) ?G° = 0, Q < K
       3. ?G > 0, Q = K                     

 

 

53. Which of the following is consistent with a reaction that proceeds spontaneously in the forward direction?
    1. 1. ?G > 0, Q < K        D) ?G° > 0, Q = K
       2. ?G° = 0, Q = K      E) ?G < 0, Q < K
       3. ?G < 0, Q > K                     

 

54. Which of the following is consistent with a reaction that proceeds spontaneously in the reverse direction (assume all variables are in terms of the forward direction only)?
    1. 1. ?G > 0, Q < K        D) ?G° > 0, Q = K
       2. ?G° = 0, Q = K      E) ?G > 0, Q > K
       3. ?G < 0, Q > K                     

 

55. The reaction rates of many spontaneous reactions are actually very slow.  Which of these statements is the best explanation for this observation?          A)        K_p for the reaction is less than one.
    1. 2. The activation energy of the reaction is large.
       3. ?G° for the reaction is positive.
       4. Such reactions are endothermic.
       5. The entropy change is negative.

 

56. The solubility product constant at 25°C for AgI(s) in water has the value 8.3 × 10^–17.

Calculate ?G_rxn at 25°C for the process AgI(s)

Ag⁺(aq) + I^– (aq) where [Ag⁺] = 9.1 × 10^–9 and [I^–] = 9.1 × 10^–9.

 

1. 1. 1. +4.4 kJ/mol D)        –91.7 kJ/mol
      2. +91.7 kJ/mol            E)        –4.4 kJ/mol
      3. 0.0 kJ/mol                 

 

57. Calculate ?G° for the combustion of ethanol vapor, C₂H₅OH(g), at 750°C in oxygen to form carbon dioxide and water vapor.  The following data is valid at 25°C:

                        

                                                             ^?H°_f (kJ/mol)         ^?G°_f (kJ/mol)

                                C₂H₅OH(g)                –234.8                     –167.9

                                O₂(g)                                0                             0

                                H₂O(g)                       –241.8                     –228.6

                                CO₂(g)                       –393.5                     –394.4

 

1. 1. 1. –1407 kJ/mol           D)        –4486 kJ/mol
      2. –2151 kJ/mol           E)        –1377 kJ/mol
      3. –1307 kJ/mol                        

 

58. Find the temperature at which the reaction N₂O₄(g)       2NO₂(g) will be in equilibrium when both gases are present at partial pressures of 1.00 atm.

                        

	?H°f (25°C)	?G°f (25°C)
NO2(g)	33.85 kJ/mol	51.8 kJ/mol
N2O4(g)	9.66 kJ/mol	98.29 kJ/mol

 

                    A)  300°C    B)  28°C    C)  55°C    D)  32°C    E)  562°C

 

59. Predict the normal boiling point of triethylborane (C₆H₁₅B) using the following data:

	?H°f (25°C)	?G°f (25°C)
C6H15B(l)	–194.6 kJ/mol	9.4 kJ/mol
C6H15B(g)	–157.7 kJ/mol	16.1 kJ/mol

 

                    A)  92°C    B)  –21°C    C)  21°C    D)  365°C    E)  256°C

 

60. A sample of solid naphthalene is introduced into an evacuated flask.  Use the data below to calculate the equilibrium vapor pressure of naphthalene (C₁₀H₈) in the flask at 35°C.

                        

                                                               ^?H°_f (25°C)           ^?G°_f (25°C)

                                C₁₀H₈(s)                   78.5 kJ/mol           201.6 kJ/mol

                                C₁₀H₈(g)                150.6 kJ/mol           224.1 kJ/mol

 

1. 1. 1. 890. mmHg D)        0.086 mmHg
      2. 0.21 mmHg E)        833 mmHg
      3. 696 mmHg              

 

61. The standard free energy of formation of gaseous hydrogen iodide is 1.30 kJ/mol at 25°C. Find K_p for the reaction H₂(g) + I₂(s)

    

    2HI(g) at this temperature.

                    A)  7.0    B)  7100    C)  1.0    D)  2.4    E)  2.9

 

62. Find the temperature at which K_p = 4.00 for the reaction N₂O₄(g)

    

    2NO₂(g). [Given: at 25°C, for NO₂(g), ?H°_f = 33.85 kJ/mol, S° = 240.46 J/mol·K; for N₂O₄(g), ?H°_f = 9.66 kJ/mol, S° = 304.3 J/mol·K; assume that ?H° and ?S° are independent of temperature.]

                    A)  197 °C    B)  56 °C    C)  36 °C    D)  79 °C    E)  476°C

 

63. Find the temperature at which K_p = 42.0 for the reaction H₂(g) + I₂(g)

    

    2HI(g).

[Given: at 25°C, for H₂(g), ?H°_f = 0, S° = 131.0 J/mol·K; for I₂(g), ?H°_f = 62.26 kJ/mol, S° = 260.6 J/mol·K; for HI(g), ?H°_f = 25.9 kJ/mol, S° = 206.3 J/mol·K; assume that ?H° and ?S° are independent of temperature.]

  A)  1040 K    B)  168 K    C)  539 K    D)  1400 K    E)  34,200 K   

 

64. For the reaction HCONH₂(g)

    

    NH₃(g) + CO(g), K_c = 4.84 at 400 K.  If ?H° for this reaction is 29 kJ/mol, find K_c at 500 K.

                    A)  5.8    B)  0.17    C)  27    D)  0.88    E)  10.3

 

65. In the gas phase, formic acid forms a dimmer, 2HCOOH(g)

    

    (HCOOH)₂(g).  For this reaction, ?H° = –60.1 kJ/mol and ?G° = –13.9 kJ/mol at 25°C.  Find the equilibrium constant (K_p) for this reaction at 75 °C.

  A)  8960    B)  273    C)  0.120    D)  8.33    E)  1.12 × 10^–4  

 

66. In the gas phase, methyl isocyanate (CH₃NC) isomerizes to acetonitrile (CH₃CN),

                         H₃C–N≡C (g)

H₃C–C≡N (g)

 

             with ?H° = –89.5 kJ/mol and ?G° = – 73.8 kJ/mol at 25°C.  Find the equilibrium constant for this reaction at 100°C.

66. 1. 1. 1.68 × 10^–10 D)        4.63 × 10^–11
       2. 5.96 × 10⁹    E)        8.64 × 10¹²
       3. 2.16 × 10¹⁰    
67. Using the thermodynamic data provided below, calculate the standard change in entropy when one mole of sodium nitrate is dissolved in water?

	S° (J/K·mol)
NaNO3(s)	116.3
Na+(aq)	60.25
NO3–(aq)	146.4

Will the solubility of sodium nitrate increase or decrease if the temperature of the system is increased?

                                            

 

68. Using the thermodynamic data provided below, calculate the standard change in entropy when one mole of sodium sulfate is dissolved in water?

	S° (J/K·mol)
Na2SO4(s)	149.49
Na+(aq)	60.25
SO42–(aq)	17.15

Will the solubility of sodium nitrate increase or decrease if the temperature of the system is increased?

                                            

 

69. For the reaction CuS(s) + H₂(g)

    

    H₂S(g) + Cu(s),

                         ?G°_f (CuS) = –53.6 kJ/mol

                         ?G°_f (H₂S) = –33.6 kJ/mol

                       ?H°_f (CuS) = –53.1 kJ/mol                ?H°_f (H₂S) = – 20.6 kJ/mol

            Will this reaction proceed spontaneously at 298 K and 1 atm pressure?

                                            

 

70. For the reaction CuS(s) + H₂(g)

    

    H₂S(g) + Cu(s),

                         ?G°_f (CuS) = –53.6 kJ/mol

                         ?G°_f (H₂S) = –33.6 kJ/mol

                       ?H°_f (CuS) = –53.1 kJ/mol                ?H°_f (H₂S) = – 20.6 kJ/mol

            Calculate the value of the equilibrium constant (K_p) for this reaction at 298 K.

                                            

 

71. For the reaction CuS(s) + H₂(g)

    

     H₂S(g) + Cu(s),

                         ?G°_f (CuS) = –53.6 kJ/mol

                         ?G°_f (H₂S) = –33.6 kJ/mol

                         ?H°_f (CuS) = –53.1 kJ/mol

                         ?H°_f (H₂S) = –20.6 kJ/mol

             Calculate ?G at 798 K and 1 atm pressure (assume ?S° and ?H° do not change with temperature).

                                           

 

72. For the reaction CuS(s) + H₂(g)

    

    H₂S(g) + Cu(s),

                         ?G°_f (CuS) = –53.6 kJ/mol

                         ?G°_f (H₂S) = –33.6 kJ/mol

                         ?H°_f (CuS) = –53.1 kJ/mol

                         ?H°_f (H₂S) = –20.6 kJ/mol

            Calculate the value of the equilibrium constant (K_p) at 798 K and 1 atm pressure.

                                           

 

73. For the reaction SbCl₅(g)

    

    SbCl₃(g) + Cl₂(g),                       ?G°_f (SbCl₅) = –334.34 kJ/mol

                         ?G°_f (SbCl₃) = –301.25 kJ/mol

                         ?H°_f (SbCl₅) = –394.34 kJ/mol

                         ?H°_f (SbCl₃) = –313.80 kJ/mol

            Will this reaction proceed spontaneously at 298 K and 1 atm pressure?

                                            

 

74. For the reaction SbCl₅(g)

    

    SbCl₃(g) + Cl₂(g),                       ?G°_f (SbCl₅) = –334.34 kJ/mol

                         ?G°_f (SbCl₃) = –301.25 kJ/mol

                         ?H°_f (SbCl₅) = –394.34 kJ/mol

                         ?H°_f (SbCl₃) = –313.80 kJ/mol

            Calculate the value of the equilibrium constant (K_p) for this reaction at 298 K.

                                            

 

75. For the reaction SbCl₅(g)

    

    SbCl₃(g) + Cl₂(g),                       ?G°_f (SbCl₅) = –334.34 kJ/mol

                         ?G°_f (SbCl₃) = –301.25 kJ/mol

                         ?H°_f (SbCl₅) = –394.34 kJ/mol

                         ?H°_f (SbCl₃) = –313.80 kJ/mol

             Calculate ?G at 800 K and 1 atm pressure (assume ?S° and ?H° do not change with temperature).

                                           

 

76. For the reaction SbCl₅(g)

    

    SbCl₃(g) + Cl₂(g),                       ?G°_f (SbCl₅) = –334.34 kJ/mol

                         ?G°_f (SbCl₃) = –301.25 kJ/mol

                         ?H°_f (SbCl₅) = –394.34 kJ/mol

                         ?H°_f (SbCl₃) = –313.80 kJ/mol

            Calculate the value of the equilibrium constant (K_p) at 800 K and 1 atm pressure.

                                           

 

77. Assuming ?S° and ?H° do not vary with temperature, at what temperature will the reaction shown below become spontaneous?

            C(s) + H₂O(g) → H₂(g) + CO(s)     (?S° = 133.6 J/K·mol; ?H° = 131.3 kJ/mol)

                                            

 

78. Rubidium has a heat of vaporization of 69.0 kJ/mol at its boiling point (686°C). Calculate

?S for this process, Rb(l) → Rb(g), at 1 atm and 686°C.

                                            

 

79. The free energy of formation of nitric oxide, NO, at 1000 K (roughly the temperature in an automobile engine during ignition) is about 78 kJ/mol. Calculate the equilibrium constant K_p for the reaction N₂(g) + O₂(g)

    

    2NO(g) at this temperature.   

                                            

 

80. Predict the signs (–, +, or 0) of ?H and ?S, in that order, for the reaction: O₂(g) → 2O(g).

                                           

 

81. Under what conditions (always, never, high temperature only, low temperature only) is the reaction O₂(g) → 2O(g) expected to be spontaneous?

                                            

 

82. Predict the signs (–, +, or 0) of ?H and ?S, in that order, for the expansion of an ideal gas into a vacuum.

                                           

 

83. Under what conditions (always, never, high temperature only, low temperature only) is the expansion of an ideal gas into a vacuum expected to be spontaneous?

                                            

 

84. Predict the signs (–, +, or 0) of ?H and ?S, in that order, for the process: H₂O(l) → H₂O(s).

                                           

 

85. Under what conditions (always, never, high temperature only, low temperature only) is the process: H₂O(l) → H₂O(s) expected to be spontaneous?

                                            

 

86. Predict the signs (–, +, or 0) of ?H and ?S, in that order, for the reaction: 6CO₂(g) +

6H₂O(g) → C₆H₁₂O₆(g) + 6O₂(g).

                                           

 

87. Under which of the following conditions (always, never, high temperature only, low temperature only) is the reaction: 6CO₂(g) + 6H₂O(g) → C₆H₁₂O₆(g) + 6O₂(g) expected to be spontaneous?

                                            

 

88. What is the free energy change for the reaction SiO₂(s) + Pb(s) → PbO₂(s) + Si(s)?               ?G°_f (PbO₂) = –217 kJ/mol

                         ?G°_f (SiO₂) = –856 kJ/mol

                                            

 

89. Is the reaction SiO₂(s) + Pb(s) → PbO₂(s) + Si(s) spontaneous?

                         ?G°_f (PbO₂) = –217 kJ/mol

                         ?G°_f (SiO₂) = –856 kJ/mol

                                            

 

90. For a certain reaction, ?G° = 87 kJ/mol, ?H° = 100 kJ/mol at STP.  At what temperature, in K, is the reaction in equilibrium, assuming that ?S° and ?H° are temperature-independent?

                                            

 

91. The heat of vaporization of water is 2.27 kJ/g.  What is ?S_vap per mole at the normal boiling point?

                                            

 

92. Calculate the free energy of formation of NaBr(s) given the following information:

                          NaBr(s) → Na(s) + ¹/₂Br₂(l), ?G° = 349 kJ/mol

 

93. The following reaction is nonspontaneous at 25°C:

                          Cu₂O(s) → 2Cu(s) + ¹/₂O₂(g), ?G° = 141 kJ/mol

             If ?S° = 75.8 J/K·mol, what is the lowest temperature at which the reaction will be spontaneous?

                                            

 

94. For the reaction 3H₂(g) + N₂(g)

    

    2NH₃(g), K_c = 9.0 at 350°C.  Calculate ?G° at 350°C.

                                            

 

95. For the reaction 3H₂(g) + N₂(g)

    

    2NH₃(g), K_c = 9.0 at 350°C.  In what direction does this reaction proceed at 350°C under standard state conditions?

                                            

 

96. For the reaction 3H₂(g) + N₂(g)

    

    2NH₃(g), K_c = 9.0 at 350°C.  What is the value of ?G at this temperature when 1.0 mol NH₃, 5.0 mol N₂, and 5.0 mol H₂ are mixed in a 2.5 L reactor?

 

97. For the reaction 3H₂(g) + N₂(g)

    

    2NH₃(g), K_c = 9.0 at 350°C.  In what direction does the reaction proceed when 1.0 mol NH₃, 5.0 mol N₂, and 5.0 mol H₂ are mixed in a 2.5 L reactor?

 

98. Consider the reaction CO(g) + 2H₂(g)

    

    CH₃OH(l) at 25°C.

                         ?G°_f (CO) = –137.3 kJ/mol

                       ?G°_f (CH₃OH) = –166.3 kJ/mol                    ?H°_f (CO) = –110.5 kJ/mol

                         ?H°_f (CH₃OH) = –238.7 kJ/mol

                       S°(CO) = 197.9 J/K·mol                     S°(CH₃OH) = 126.8 J/K·mol

            Calculate ?G° at 25°C.

                                            

 

99. Consider the reaction  CO(g) + 2H₂(g)

    

    CH₃OH(l) at 25°C.

                         ?G°_f (CO) = –137.3 kJ/mol

                       ?G°_f (CH₃OH) = –166.3 kJ/mol                    ?H°_f (CO) = –110.5 kJ/mol

                         ?H°_f (CH₃OH) = –238.7 kJ/mol

                         S°(CO) = 197.9 J/K·mol

                         S°(CH₃OH) = 126.8 J/K·mol

             Calculate value of the equilibrium constant (K_p) for this reaction at 25°C.

                                            

 

100. Consider the reaction CO(g) + 2H₂(g)

     

     CH₃OH(l) at 25°C.

                         ?G°_f (CO) = –137.3 kJ/mol

                       ?G°_f (CH₃OH) = –166.3 kJ/mol                    ?H°_f (CO) = –110.5 kJ/mol

                         ?H°_f (CH₃OH) = –238.7 kJ/mol

                       S°(CO) = 197.9 J/K·mol                     S°(CH₃OH) = 126.8 J/K·mol              Calculate S°(H₂(g))_.

 

101. For the reaction H₂O₂(g) → H₂O(g) + ¹/₂O₂(g), ?H° = –106 kJ/mol and ?S° = 58 J/K·mol at 25°C.  Calculate ?G° for this reaction at this temperature.

                                            

 

102. For the reaction H₂O₂(g) → H₂O(g) + ¹/₂O₂(g), ?H° = –106 kJ/mol and ?S° = 58 J/K·mol at 25°C.  Is H₂O₂(g) stable with respect to dissociation into water vapor and oxygen gas at 25°C?

                                            

 

103. Choose the substance with the higher entropy per mole at a given temperature: O₂(g) at 5 atm or O₂(g) at 0.5 atm.

                                           

 

104. Choose the substance with the higher entropy per mole at a given temperature: Br₂(l) or Br₂(g).

                                           

 

105. Choose the substance with the higher entropy per mole at a given temperature: 1 mole of N₂(g) in a 22.4 L container or 1 mole of N₂(g) in a 2.24 L container.

                                           

 

106. Choose the substance with the higher entropy per mole at a given temperature: CO₂(g) or CO₂(aq).

                                           

 

107. ?H_vap for ethanol is 38.7 kJ/mol at its boiling point (78°C). What is ?S_surr when 1.00 mole of ethanol is boiled?

                                            

 

108. Using the thermodynamic data provided below, determine the temperature in °C at which the decomposition of solid calcium carbonate to form solid calcium oxide and oxygen becomes spontaneous.                   

	?H°f (kJ/mol)	S° (J/K·mol)
CO2(g)	–393.5	213.6
CaO(s)	–635.6	39.8
CaCO3(s)	–1206.9	92.9

           

                                            

 

109. Sulfur can be separated from lead in the mineral galena, PbS(s), by “roasting” the ore in the presence of oxygen as shown in the following reaction:

                       2PbS(s) + 3O₂(g) → 2PbO(s) + 2SO₂(g)           Determine ?G for the above reaction at 850°C.

                        

	?H°f (kJ/mol)	S°(J/K·mol)
PbS(s)	–94.3	91.2
O2(g)	0	205.0
PbO(s)	–217.86	69.45
SO2(g)	–296.4	248.5

           

                                            

 

110. Given the following data, calculate the boiling point of HCOOH (formic acid).

                        

            ^?H°_f (kJ/mol) S° (J/K·mol) HCOOH(l)         –410    130

                                HCOOH(g)                –363                         251

          

                                            

 

111. Given the following data, estimate the boiling point of carbon disulfide, CS₂, assuming that ?S° and ?H° are temperature-independent.                     

	?H°f (kJ/mol)	S° (J/K·mol)
CS2(g)	115.3	237.8
CS2(l)	87.3	151.0

           

                                            

 

112. Given the following data, estimate the boiling point of bromine, Br₂, assuming that ?S° and ?H° are temperature-independent.                       

	?H°f (kJ/mol)	S° (J/K·mol)
Br2(g)	30.91	245.3
Br2(l)	0	152.3

           

                                            

 

113. At 700 K, the equilibrium constant for the reaction CO(g) + H₂O(g)

     

     CO₂(g) + H₂(g) is 5.10. What is ?G° for this reaction at this temperature?

                                            

 

114. Using the thermodynamic data provided below, calculate K_a for HCN(aq) at 25°.                  

	?H°f (kJ/mol)	S° (J/K·mol)
H+(aq)	0	0
CN–(aq)	151.0	117.99
HCN(aq)	105.4	128.9

           

 

115. Using the thermodynamic data provided below, calculate K_a1 for H₂CO₃(aq) at 25°.                           

	?H°f (kJ/mol)	S° (J/K·mol)
H+(aq)	0	0
H2CO3(aq)	–698.7	191
HCO3–(aq)	–691.11	95.0
CO32– (aq)	–676.26	–53.1

           

 

116. Using the thermodynamic data provided below, calculate K_a2 for H₂CO₃(aq) at 25°.                           

	?H°f (kJ/mol)	S° (J/K·mol)
H+(aq)	0	0
H2CO3(aq)	–698.7	191
HCO3–(aq)	–691.11	95.0
CO32– (aq)	–676.26	–53.1

           

                                            

 

117. Using the thermodynamic data provided below, calculate K_sp for ZnS(s) at 25°.                      

	?H°f (kJ/mol)	S° (J/K·mol)
Zn2+(aq)	–152.4	–106.5
S2–(aq)	41.8	22
ZnS(s)	–203	57.7

           

 

118. Using the thermodynamic data provided below, calculate K_sp for Mg(OH)₂(s) at 25°.                         

	?H°f (kJ/mol)	S° (J/K·mol)
Mg2+(aq)	–461.96	–117.99
OH–(aq)	–229.94	–10.5
Mg(OH)2(s)	–924.66	63.1

           

                                            

 

119. The standard entropy of any pure substance is 0 J/mol.

 

120. The entropy of any pure substance at 0 K is 0 J/mol.

 

121. The entropy of a perfectly ordered crystalline substance at 0 K is 0 J/mol.

 

122. Melting an ionic solid always results in an increase in entropy.

 

123. Dissolving an ionic solid in water always results in an increase in entropy.

 

124. For a given substance the entropy always increases in the following order:

                          S (gas) < S (liq) < S (solid).

 

125. The entropy change ?S° for the reaction NH₄Cl(s) → NH₃(g) + HCl(g) will be negative.

 

126. The following reaction is spontaneous under standard state conditions at 25°C:

                          AgCl(s) → Ag⁺(aq) + Cl^–(aq)   (?G° = 55 kJ/mol)

 

127. For any pure substance, if ?H_f° = 0 and ?G_f° = 0, than S° = 0