Note 538 — Chapter XIV · OXIDATION AND REDUCTION REACTIONS. I

Equilibrium will be established whenever the potential of the system is equal to 0. The potential of the system may be calculated according to the equation (see footnote 1, p. 262)

ε_{Cu, Zn} = ε_{Cu, CuSO4} − ε_{Zn, ZnSO4} = (0.0575 / 2) [log(Cu²⁺ / K_Cu) − log(Zn²⁺ / K_Zn)].

The potential ε_{Cu, Zn} is 0 whenever [Cu²⁺] / K_Cu = [Zn²⁺] / K_Zn, i.e. when [Zn²⁺] / [Cu²⁺] = K_Zn / K_Cu.

For ions of different valence, such as silver and cupric ions, the equilibrium equation assumes a somewhat less simple form. For Cu ↓ + 2 Ag⁺ ⇄ 2 Ag ↓ + Cu²⁺, we have [Ag⁺]² / [Cu²⁺] = (K_Ag)² / K_Cu.