The electrolysis of NaCl(aq) leads to a somewhat unexpected result.
At the cathode H2O is reduced to H2 .
The possible reactions at the anode are the oxidation of H2O(l), or the oxidation of Cl–(aq):
Based on the values, we would expect H2O to be oxidized in preference to Cl–. Experiments show, however, that Cl– is oxidized rather than H2O because of over-voltage(over-potential).
This counterintuitive result occurs because of the kinetics of the electrode process—in essence, even though the oxidation of H2O is thermodynamically favored,
the activation energy for the oxidation of Cl– is lower, so it is kinetically favored.
The observed cell reactions for the electrolysis of NaCl(aq) are summarized as follows:
This electrolytic process is industrially significant because the reactants are plentiful and the products—H2, Cl2 and NaOH—are important commercial substances.