If a galvanic cell has E°cell = 0.54 V and transfers 3 electrons (n = 3), what is ΔG° for the reaction?

• A. +1.2 kJ/mol
• B. -520 kJ/mol
• C. +156 kJ/mol
• D. -156 kJ/mol

Answer: (D)

This question hinges on how standard Gibbs free energy change relates to the standard cell potential. For a galvanic cell, ΔG° = -n F E°cell, where n is the number of electrons transferred, F is Faraday’s constant (~96485 C/mol), and E°cell is the standard cell potential in volts.

With n = 3 and E°cell = 0.54 V, compute ΔG° = -(3)(96485 C/mol)(0.54 V) ≈ -156,000 J/mol ≈ -156 kJ/mol. The negative sign shows the reaction is spontaneous under standard conditions.

Thus, the standard Gibbs energy change is about -156 kJ/mol.