Electrochemistry

 

 44) (a) F = 96500 J/V•mol

 

                                 2I-(aq) I2(s) + 2e-              red = 0.536 V

                   Hg22+(aq) + 2e- 2Hg(l)                E°red = 0.789 V
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             2I-(aq) + Hg22+(aq) I2(s) + 2Hg(l)     E°red = 0.253 V

             

             E° = E°red(reduction) - E°red(oxidation)

             E° = 0.789 V - 0.536 V = 0.253 V

 

             ΔG° = -nFE° = -2 mol e- x 96500 J/Vmol e- x 0.253 V x 1 kJ/103 J = -48.8 kJ

                

       (b)

                                                  3Cu+(aq) 3Cu2+(aq) + 3e-                                   E°red = 0.153 V

                       NO3-(aq) + 4H+(aq) + 3e- NO(g) + 2H2O(l)                              E°red = 0.96 V
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             3Cu+(aq) + NO3-(aq) + 4H+(aq) 3Cu2+(aq) + NO(g) + 2H2O(l)         E°red = 0.81 V

             

             E° = E°red(reduction) - E°red(oxidation)

             E° = 0.96 V - 0.153 V = 0.81 V

 

             ΔG° = -nFE° = -3 mol e- x 96500 J/Vmol e- x 0.81 V x 1 kJ/103 J = -230 kJ

 

       (c)

                       Cr(OH)3(s) + 5OH-(aq) CrO42-(aq) + 4H2O(l) + 3e-                                   

                       ClO-(aq) + H2O(l) + 2e- Cl-(aq) + 2OH-(aq)                             

 

                                                         4                                                   5

                               2Cr(OH)3(s) + 10OH-(aq) 2CrO42-(aq) + 8H2O(l) + 6e-                    E°red = -0.13 V

                               3ClO-(aq) + 3H2O(l) + 6e- 3Cl-(aq) + 6OH-(aq)                             E°red = 0.89 V
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             2Cr(OH)3(s) + 4OH-(aq) + 3ClO-(aq) 2CrO42-(aq) + 5H2O(l) + 3Cl-(aq)       E°red = 1.02 V

             

             E° = E°red(reduction) - E°red(oxidation)

             E° = 0.89 V - (-0.13 V) = 1.02 V

 

             ΔG° = -nFE° = -6 mol e- x 96500 J/Vmol e- x 1.02 V x 1 kJ/103 J = -591 kJ