Faraday constant
/ FAIR-uh-day KON-stant /
Suppose you could count out one mole of electrons — about 600 billion trillion of them — and ask how much electric charge they carry all together. That single, fixed amount of charge is the Faraday constant. It is the bridge that lets you swap freely between the language of moles (how chemists count) and the language of coulombs (how electricity is measured).
Numerically it is about 96,485 coulombs per mole of electrons. You get it by multiplying the charge on one electron by the Avogadro constant — the number of particles in a mole. Wherever a reaction transfers electrons, the Faraday constant converts the moles of electrons into the charge that must flow, and vice versa.
This constant is what makes electrochemistry quantitative. It sits inside Faraday's laws (linking charge passed to mass deposited) and inside the Nernst equation (linking voltage to free energy). Whenever you calculate how long to plate a part, or how much energy a battery can store, the Faraday constant is doing the translation between chemistry and electricity.
To deposit one mole of silver (each ion needing just one electron), you must pass one mole of electrons — about 96,485 coulombs. At a steady 1 ampere, that takes roughly 27 hours.
One mole of electrons carries about 96,485 coulombs — that is the Faraday constant.
Don't confuse the Faraday constant (charge per mole of electrons, in coulombs) with the farad (the unit of capacitance). Both honor Michael Faraday, but they measure entirely different things.