An oxidation-reduction reaction in which 3 electrons are transferred has a Delta G° = 18.55 kJ/mol at 25 degrees C. What is the value of E°?

• A. 0.192 V
• B. -0.064 V
• C. -0.192 V
• D. -0.577 V

Answer: (A)

The relationship between Gibbs free energy and standard cell potential is ΔG° = -n F E°. Here n is the number of electrons transferred, and F is Faraday’s constant (96485 C/mol). Solve for E°: E° = -ΔG°/(nF).

Convert ΔG° to joules: 18.55 kJ/mol = 18550 J/mol. With n = 3 and F = 96485 C/mol, E° = -18550 / (3 × 96485) ≈ -0.064 V.

So the standard reduction potential is about -0.064 V. The negative sign means the reaction, as written, is non-spontaneous under standard conditions; the reverse reaction would be spontaneous.