The common value I0 of the anodic and cathodic partial currents when the reaction is at equilibrium \[I_{0}=I_{\text{a}}=- I_{\text{c}}\] For an electrode at equilibrium at which only one reaction is significant I = 0. When more than one reaction is significant at a given electrode, subscripts to I0 may be used to distinguish exchange currents. I is not usually zero when only one of these reactions is at equilibrium.