How much electrical energy is required to generate 1.000L of H, at 25°C and 1.00 atm pressure by the electrolysis of water?

The electrical energy required : 0.082 F

Given

1.000L of H₂ at 25°C and 1.00 atm

Required

Electrical energy

Solution

Redox reactions in water electrolysis :

Anode: 2H2O (l) → O2 (g) + 4H⁺ (aq) + 4e

Cathode: 4H2O (l) + 4e → 2H2 (g) + 4OH⁻ (aq)

Reaction: 2H2O → 2H2 (g) + O2 (g)

mol H₂ :

n = PV/RT

n = (1 atm x 1 L)/(0.082 x 298)

n = 0.041

From reaction at cathode : mol ratio of electron and H₂ = 4 : 2, so mol electrons :

= 4/2 x mol H₂

= 2 x 0.041

= 0.082

1 Faraday is the amount of electricity that is passed in the electrolysis cell to obtain 1 mole of electrons.

1 Faraday = 1 mole of electrons = 96500 Coulombs

So the energy required :

0.082 Faraday