ΔG° can be calculated from the cell potential using the following equation:
ΔG° = Gibbs Free Energy, J
n = # of e- transferred
F = Faraday’s constant = 96485 J/(mol e-)
E°cell = standard cell potential, V
ΔG°f for Fe2+(aq):
Fe2+(aq) + 2 e- → Fe(s) E° = -0.447 V
n = 2 mol e-
F = 96485 C/(mol e-)
E° = -0.447 V
ΔG°rxn = 86257.59 J
ΔG°rxn = 86.26 kJ
ΔG˚f, Fe2+ = –86.26 kJ/mol Fe2+
ΔG°f for Fe3+(aq):
The equation ΔG° = -nFE° also can be applied to half-reactions. Use standard reduction potentials to estimate ΔG°f for Fe2+(aq) and Fe3+(aq). (ΔG°f for e- = 0.)
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