For the cell with E°cell = 0.80 V transferring 3 moles of electrons, what is ΔG° at 25°C?

• A. -231.6 kJ/mol
• B. -1.23 kJ/mol
• C. -12.3 kJ/mol
• D. -999 kJ/mol

Answer: (B)

The key idea is that the standard free energy change for an electrochemical reaction is ΔG° = −n F E°cell, where n is the number of moles of electrons transferred. Here, 3 moles of electrons are involved, F is Faraday’s constant (96485 C/mol e−), and E°cell is 0.80 V. Plugging in, ΔG° = −(3)(96485 C/mol)(0.80 V) = −231,564 J per mole of reaction, which is about −231.6 kJ. The negative sign shows the reaction releases energy under standard conditions. Since the question specifies transferring 3 electrons, the total ΔG° is about −231.6 kJ, not the smaller values given by misapplying the formula or units.