Electrochemistry

 44) (a) F = 96500 J/V•mol

                                 2I^-(aq) I₂(s) + 2e^-              E°_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/V•mol 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/V•mol e^- x 0.81 V x 1 kJ/10³ J = -230 kJ

       (c)

                       Cr(OH)₃(s) + 5OH^-(aq) CrO₄^2-(aq) + 4H₂O(l) + 3e^-                                   

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

                                                         4                                                   5

                               2Cr(OH)₃(s) + 10OH^-(aq) 2CrO₄^2-(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) 2CrO₄^2-(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/V•mol e^- x 1.02 V x 1 kJ/10³ J = -591 kJ