redox reaction drives the cell to produce an electric potential, Gibbs free energy must be negative, in accordance with the following equation:

: (unit: Joule = Coulomb × Volt)

where is number of moles of electrons per mole of products and is the Faraday constant, ~ 96 485 C/mol.

As such, the following rules apply:

: If > 0, then the process is spontaneous (galvanic cell):