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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)

Chemistry

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    

 

  1. 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)

 

 

  1. 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    

 

  1. 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)

 

 

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

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

      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)

 

 

  1. 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)

 

 

  1. Which one of the following reactions would you expect to have the lowest ?S°?
      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)

 

 

  1. Which one of the following reactions would you expect to have highest ?S°?
      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)

 

 

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

 

 

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

 

 

  1. 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    

 

  1. Without reference to a table, arrange these reactions according to increasing ?S.
        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

 

 

  1. Arrange these reactions according to increasing ?S.
        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    

 

  1. Which of the following processes would be accompanied by an increase in entropy?
      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)                 

 

 

  1. Which of the following processes would be accompanied by a decrease in entropy?
      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)                  

 

 

  1. Which of the following is expected to have zero entropy?
      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

 

 

  1. 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. 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                     

 

 

  1. 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                                                  

 

 

  1. 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

 

 

 

 

  1. 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

 

 

 

 

  1. 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

 

 

 

 

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

 

 

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

 

 

  1. HI has a normal boiling point of –35.4°C, and its ?Hvap is 21.16 kJ/mol.  Calculate the molar entropy of vaporization (?Svap).
      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                         

 

 

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

 

 

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

 

 

  1. Which of the following is consistent with a spontaneous endothermic reaction?
      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                 

 

 

  1. Which of the following is consistent with an exothermic reaction that is spontaneous at all temperatures?    
      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                 

 

 

  1. Which of the following is consistent with an exothermic reaction that is nonspontaneous at high temperatures? 
      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                             

 

 

  1. 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 ?f of aluminum oxide is –1576.4 kJ/mol.

      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                       

 

 

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

 

 

 

 

  1. 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. 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                 

 

 

  1. 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

 

 

  1. 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

 

 

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

 

 

  1. 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

 

 

  1. 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. ?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                             

 

 

  1. 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. ?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                 

 

 

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

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

             Calculate Kp 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      

 

  1. At 1500°C the equilibrium constant for the reaction CO(g) + 2H2(g)
    CH3OH(g) has the value Kp = 1.4 × 10–7.  Calculate ?G° for this reaction at 1500°C.
      1. 105 kJ/mol   D)        –105 kJ/mol
      2. 1.07 kJ/mol E)        233 kJ/mol
      3. –233 kJ/mol                          

 

 

  1. Calculate Kp at 298 K for the reaction SO2(g) + NO2(g)
     SO3(g) + NO(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      

 

  1. The equilibrium constant at 427°C for the reaction N2(g) + 3H2(g)
    2NH3(g) is Kp =

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

 

 

  1. Determine the equilibrium constant Kp at 25°C for the reaction N2(g) + 3H2(g)
    2NH3(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      

 

  1. Calculate the equilibrium constant for the decomposition of water                 2H2O(l)
    2H2(g) + O2(g)       at 25°C, given that ?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      

 

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

             2NOCl(g)

2NO(g) + Cl2(g).  Calculate Kp 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      

 

  1. The equilibrium constant for the reaction AgBr(s)
    Ag+(aq) + Br(aq) is the solubility product constant, Ksp = 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. ?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

 

  1. 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. +207.8 kJ/mol          D)        +17.3 kJ/mol
      2. +226.3 kJ/mol          E)        –16.9 kJ/mol
      3. +192.1 kJ/mol                       

 

 

  1. 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. –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                       

 

 

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

 

 

  1. Determine the equilibrium constant (Kp) 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      

 

  1. Kw 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. ?S° = (+) and ?H° = (+)    C) ?S° = (–) and ?H° = (+)
      2. ?S° = (+) and ?H° = (–)    D) ?S° = (–) and ?H° = (–)

 

 

  1. Which of the following is consistent with a reaction at equilibrium?
      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                     

 

 

  1. Which of the following is consistent with a reaction that proceeds spontaneously in the forward direction?
      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                     

 

  1. 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. ?G > 0, Q < K        D) ?G° > 0, Q = K
      2. ?G° = 0, Q = K      E) ?G > 0, Q > K
      3. ?G < 0, Q > K                     

 

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

 

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

Calculate ?Grxn 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. +4.4 kJ/mol D)        –91.7 kJ/mol
      2. +91.7 kJ/mol            E)        –4.4 kJ/mol
      3. 0.0 kJ/mol                 

 

  1. 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:

                        

                                                             ?f (kJ/mol)         ?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. –1407 kJ/mol           D)        –4486 kJ/mol
      2. –2151 kJ/mol           E)        –1377 kJ/mol
      3. –1307 kJ/mol                        

 

  1. 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.

                        

 

?f (25°C)

?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

 

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

                        

 

 

 

?f (25°C)

?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

 

  1. 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.

                        

                                                               ?f (25°C)           ?f (25°C)

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

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

 

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

 

  1. The standard free energy of formation of gaseous hydrogen iodide is 1.30 kJ/mol at 25°C. Find Kp 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

 

  1. Find the temperature at which Kp = 4.00 for the reaction N2O4(g)
    2NO2(g). [Given: at 25°C, for NO2(g), ?f = 33.85 kJ/mol, S° = 240.46 J/mol·K; for N2O4(g), ?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

 

  1. Find the temperature at which Kp = 42.0 for the reaction H2(g) + I2(g)
    2HI(g).

[Given: at 25°C, for H2(g), ?f = 0, S° = 131.0 J/mol·K; for I2(g), ?f = 62.26 kJ/mol, S° = 260.6 J/mol·K; for HI(g), ?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   

 

  1. For the reaction HCONH2(g)
    NH3(g) + CO(g), Kc = 4.84 at 400 K.  If ?H° for this reaction is 29 kJ/mol, find Kc at 500 K.

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

 

  1. 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 (Kp) for this reaction at 75 °C.

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

 

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

                         H3C–NC (g)

H3C–CN (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.

      1. 1.68 × 10–10 D)        4.63 × 10–11
      2. 5.96 × 109    E)        8.64 × 1012
      3. 2.16 × 1010    
  1. 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?

                                            

 

  1. 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?

                                            

 

  1. For the reaction CuS(s) + H2(g)
    H2S(g) + Cu(s),

                         ?f (CuS) = –53.6 kJ/mol

                         ?f (H2S) = –33.6 kJ/mol

                       ?f (CuS) = –53.1 kJ/mol                ?f (H2S) = – 20.6 kJ/mol

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

                                            

 

  1. For the reaction CuS(s) + H2(g)
    H2S(g) + Cu(s),

                         ?f (CuS) = –53.6 kJ/mol

                         ?f (H2S) = –33.6 kJ/mol

                       ?f (CuS) = –53.1 kJ/mol                ?f (H2S) = – 20.6 kJ/mol

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

                                            

 

  1. For the reaction CuS(s) + H2(g)
     H2S(g) + Cu(s),

                         ?f (CuS) = –53.6 kJ/mol

                         ?f (H2S) = –33.6 kJ/mol

                         ?f (CuS) = –53.1 kJ/mol

                         ?f (H2S) = –20.6 kJ/mol

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

                                           

 

  1. For the reaction CuS(s) + H2(g)
    H2S(g) + Cu(s),

                         ?f (CuS) = –53.6 kJ/mol

                         ?f (H2S) = –33.6 kJ/mol

                         ?f (CuS) = –53.1 kJ/mol

                         ?f (H2S) = –20.6 kJ/mol

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

                                           

 

  1. For the reaction SbCl5(g)
    SbCl3(g) + Cl2(g),                       ?f (SbCl5) = –334.34 kJ/mol

                         ?f (SbCl3) = –301.25 kJ/mol

                         ?f (SbCl5) = –394.34 kJ/mol

                         ?f (SbCl3) = –313.80 kJ/mol

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

                                            

 

  1. For the reaction SbCl5(g)
    SbCl3(g) + Cl2(g),                       ?f (SbCl5) = –334.34 kJ/mol

                         ?f (SbCl3) = –301.25 kJ/mol

                         ?f (SbCl5) = –394.34 kJ/mol

                         ?f (SbCl3) = –313.80 kJ/mol

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

                                            

 

  1. For the reaction SbCl5(g)
    SbCl3(g) + Cl2(g),                       ?f (SbCl5) = –334.34 kJ/mol

                         ?f (SbCl3) = –301.25 kJ/mol

                         ?f (SbCl5) = –394.34 kJ/mol

                         ?f (SbCl3) = –313.80 kJ/mol

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

                                           

 

  1. For the reaction SbCl5(g)
    SbCl3(g) + Cl2(g),                       ?f (SbCl5) = –334.34 kJ/mol

                         ?f (SbCl3) = –301.25 kJ/mol

                         ?f (SbCl5) = –394.34 kJ/mol

                         ?f (SbCl3) = –313.80 kJ/mol

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

                                           

 

  1. 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)

                                            

 

  1. 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.

                                            

 

  1. 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 Kp for the reaction N2(g) + O2(g)
    2NO(g) at this temperature.   

                                            

 

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

                                           

 

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

                                            

 

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

                                           

 

  1. 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?

                                            

 

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

                                           

 

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

                                            

 

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

6H2O(g) C6H12O6(g) + 6O2(g).

                                           

 

  1. 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?

                                            

 

  1. What is the free energy change for the reaction SiO2(s) + Pb(s) PbO2(s) + Si(s)?               ?f (PbO2) = –217 kJ/mol

                         ?f (SiO2) = –856 kJ/mol

                                            

 

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

                         ?f (PbO2) = –217 kJ/mol

                         ?f (SiO2) = –856 kJ/mol

                                            

 

  1. 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?

                                            

 

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

                                            

 

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

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

 

  1. 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?

                                            

 

  1. For the reaction 3H2(g) + N2(g)
    2NH3(g), Kc = 9.0 at 350°C.  Calculate ?G° at 350°C.

                                            

 

  1. For the reaction 3H2(g) + N2(g)
    2NH3(g), Kc = 9.0 at 350°C.  In what direction does this reaction proceed at 350°C under standard state conditions?

                                            

 

  1. For the reaction 3H2(g) + N2(g)
    2NH3(g), Kc = 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?

 

  1. For the reaction 3H2(g) + N2(g)
    2NH3(g), Kc = 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?

 

  1. Consider the reaction CO(g) + 2H2(g)
    CH3OH(l) at 25°C.

                         ?f (CO) = –137.3 kJ/mol

                       ?f (CH3OH) = –166.3 kJ/mol                    ?f (CO) = –110.5 kJ/mol

                         ?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.

                                            

 

  1. Consider the reaction  CO(g) + 2H2(g)
    CH3OH(l) at 25°C.

                         ?f (CO) = –137.3 kJ/mol

                       ?f (CH3OH) = –166.3 kJ/mol                    ?f (CO) = –110.5 kJ/mol

                         ?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 (Kp) for this reaction at 25°C.

                                            

 

  1. Consider the reaction CO(g) + 2H2(g)
    CH3OH(l) at 25°C.

                         ?f (CO) = –137.3 kJ/mol

                       ?f (CH3OH) = –166.3 kJ/mol                    ?f (CO) = –110.5 kJ/mol

                         ?f (CH3OH) = –238.7 kJ/mol

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

 

  1. 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.

                                            

 

  1. 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?

                                            

 

  1. 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.

                                           

 

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

                                           

 

  1. 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.

                                           

 

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

                                           

 

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

                                            

 

  1. 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.                   

 

?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

           

                                            

 

  1. 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.

                        

 

?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

           

                                            

 

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

                        

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

                                HCOOH(g)                –363                         251

          

                                            

 

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

 

?f (kJ/mol)   

S° (J/K·mol)

CS2(g)

      115.3

     237.8

CS2(l)

        87.3

     151.0

           

                                            

 

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

 

?f (kJ/mol)   

S° (J/K·mol)

Br2(g)

      30.91

   245.3

Br2(l)

        0

   152.3

           

                                            

 

  1. 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?

                                            

 

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

 

?f (kJ/mol)

S° (J/K·mol)

H+(aq)

        0

         0

CN(aq)

    151.0

    117.99

HCN(aq)

    105.4

    128.9

           

 

  1. Using the thermodynamic data provided below, calculate Ka1 for H2CO3(aq) at 25°.                           

 

?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

           

 

  1. Using the thermodynamic data provided below, calculate Ka2 for H2CO3(aq) at 25°.                           

 

?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

           

                                            

 

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

 

?f (kJ/mol)

S° (J/K·mol)

Zn2+(aq)

  –152.4

  –106.5

S2–(aq)

       41.8

      22

ZnS(s)

  –203

      57.7

           

 

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

 

?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

           

                                            

 

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

 

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

 

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

 

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

 

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

 

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

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

 

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

 

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

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

 

  1. For any pure substance, if ?Hf° = 0 and ?Gf° = 0, than S° = 0

 

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