reaction at the cathode may be written as the sum of ( . ) and ( . ) and we have H O ( l ) + e – ® ½H (g) + OH – ( . ) At the anode the following oxidation reactions are possible: Cl – (aq) ® ½ Cl (g) + e – = .
V ( . ) 2H O ( l ) ® O (g) + 4H + (aq) + 4e – = . V ( . ) The reaction at anode with lower value of E o is preferred and therefore, water should get oxidised in preference to Cl – (aq).
However, on account of overpotential of oxygen, reaction ( . ) is preferred. Thus, the net reactions may be summarised as: NaCl (aq) H O → Na + (aq) + Cl – (aq) Cathode: H O( l ) + e – ® ½ H (g) + OH – (aq) Anode: Cl – (aq) ® ½ Cl (g) + e – Net reaction: NaCl(aq) + H O( l ) ® Na + (aq) + OH – (aq) + ½H (g) + ½Cl (g) The standard electrode potentials are replaced by electrode potentials given by Nernst equation (Eq. .
) to take into account the concentration effects. During the electrolysis of sulphuric acid, the following processes are possible at the anode: 2H O(l) ® O (g) + 4H + (aq) + 4e – = + . V ( . ) 2SO – (aq) ® S O – (aq) + 2e – = .
V ( . ) For dilute sulphuric acid, reaction ( . ) is preferred but at higher concentrations of H SO , reaction ( . ) is preferred.
Any battery (actually it may have one or more than one cell connected in series) or cell that we use as a source of electrical energy is basically a galvanic cell where the chemical energy of the redox reaction is converted into electrical energy. However, for a battery to be of practical use it should be reasonably light, compact and its voltage should not