Notion of electrochemical equilibrium
Standard potentials of aqueous solutions

In the broadest sense, an electrochemical equilibrium involves (at least) two hydrated species, with different oxidation numbers .

Let Ox and Red be species such that the oxidation number of Ox is greater than that of Red. When mixed in solution, these species interact in an equilibrium involving electrons. The (electrochemical) equilibrium is characteristic of the conjugated redox couple thus formed.

If n is the number of electrons (e ^– ) exchanged, the equilibrium is written :...