What is the unit of Faraday's constant?

• A. J/mol
• B. C/mol
• C. Pa·m^3/mol
• D. A·s/mol

Answer: (B)

Faraday's constant tells us how much electric charge is carried by a given amount of substance in moles of electrons. The key relationship is Q = nF, where Q is the total charge in coulombs and n is the amount of substance in moles. To make the units consistent, F must have units of charge per mole, so Coulombs per mole (C/mol). That way, multiplying by the amount in moles gives a total charge in coulombs: (mol) × (C/mol) = C.

Numerically, F equals e times Avogadro's number, since one mole of electrons carries e × N_A coulombs, which is about 96485 C/mol.

Other units listed describe energy per mole (J/mol) or are not aligned with charge (Pa·m^3/mol), so they don’t fit the quantity Faraday's constant represents. A·s/mol is equivalent to C/mol (since 1 C = 1 A·s) but the standard, widely used expression is C/mol.