Faraday's constant

Meaning: F is the charge on one mole of electrons. It equals the elementary charge (1.60 × 10⁻¹⁹ C) times Avogadro's number (6.02 × 10²³ per mol), which gives 96,485 C/mol. The MCAT usually rounds this to 96,500 or 9.65 × 10⁴ C/mol. It is the bridge between electrical quantities (coulombs, amperes, volts) and chemical amounts (moles).

Equation: ΔG = −nFE, where ΔG is the free energy change in J/mol of reaction, n is the moles of electrons transferred per mole of reaction (mol e⁻/mol), F is Faraday's constant in C/mol e⁻, and E is the cell potential in V (1 V = 1 J/C).

On the MCAT: Two uses are common. In electrolysis, a passage gives a current and a time. Charge is Q = It, with I in A and t in s. Moles of electrons are Q/F. Use the half-reaction stoichiometry to convert to moles or grams of metal plated. For example, Cu²⁺ + 2e⁻ → Cu takes 2 mol e⁻ per mol Cu. In thermodynamics, you may be asked to find ΔG from E. A positive E gives a negative ΔG, which means a spontaneous reaction. The answer must come out in J, not kJ, unless you convert.

Common confusion: F is not the charge of a single electron. That is e, 1.60 × 10⁻¹⁹ C. F is the charge per mole of electrons. Also, n counts moles of electrons in the balanced equation, not moles of reactant. Doubling the coefficients doubles n but leaves E unchanged.