The magnitude of the standard electrode potential is a measure of the tendency of the half reaction to occur in the forward direction, i.e., in the direction of reduction. Thus, if any element exists in more than one oxidation state, their relative stabilities can be known from the standard electrode potential data. For example in case of copper, we have ‌A2++2e−⟶A;E0=+0.34V ‌A++2e−⟶A;E0=+0.52V Thus, Cu+is reduced more easily hence less stable than Cu2+. This is because although second ionisaton enthalpy of copper is large but enthalpy of hydration for Cu2+ (aq) is much more negative than that for Cu+(aq) and hence it more than compensates for the second ionisation enthalpy of copper.