Compute ΔG° for n=2, E°cell=0.40 V.

• A. -77 kJ/mol
• B. -38 kJ/mol
• C. -160 kJ/mol
• D. -8 kJ/mol

Answer: (A)

The relationship between Gibbs free energy change and cell potential is ΔG° = −n F E°cell. Here, n is the number of electrons transferred, F ≈ 96485 C/mol, and E°cell = 0.40 V. So ΔG° = −(2)(96485)(0.40) J/mol ≈ −77,190 J/mol, which is about −77 kJ/mol. The negative sign shows the reaction is spontaneous under standard conditions for this cell potential.