Faraday Constant

A mole of electrons is given a special name: 1 Faraday. The charge of 1 mole of electrons is called the Faraday Constant, F.

It is calculated by multiplying the charge of one electron by the Avogadro constant.

1 Faraday = 9.648 70 x 104, coulombs/faraday (C mol-1).

In electrolysis, Michael Faraday in 1832 - 1833 discovered the relationship between the charge and the quantity of matter liberated in an electrode reaction. He did not know about partial reactions at electrodes, electrons, or a unit (to be) named after him. He did know something about atomic and molecular masses. His results are summarised in two laws, now famous as Faraday's laws.

  1. The mass of a substance produced or consumed is proportional to the quantity of charge (current x time) that has passed through the circuit.

  2. The number of faradays that must pass through a circuit when one mole of a substance is produced or consumed is a whole number.
What the whole number is depends on the substance and the reaction. For example:

2 faradays produce 1 mol of H2:
2H+ + 2e- ® H2

1 faraday produces 1 mol of Ag:
Ag+ + e- ® Ag

3 faradays produce 1 mol of Al:
Al3+ + 3e- ® Al

That one mole of atoms or molecules always requires an integral number of faradays suggests a once novel but now familiar idea: the existence of a natural unit of charge, the charge of an electron.

See also Avogadro Constant | The Mole