Calculate the work of expansion when 100 g of water is electrolysed at a constant pressure of 1 tm and temperature of 25°C.

Electrolysis of water:

2H₂O(l) → 2H₂(g) + O₂(g)

Thus, 2 moles of H₂O (2 × 18 = 36 g) on electrolysis produce 2 moles of H₂ gas and 1 mole of O₂ gas, i.e., total 3 moles of gases.

∴ 100 g of water will produce gases = (3/36) × 100 = 8.33 moles

Volume occupied by 8.33 moles of gases at 25°C and 1 atm pressure:

V = (nRT)/P = (8.33 moles)(0.0821 L atm K⁻¹ mol⁻¹)(298 K) / (1 atm) = 203.8 L

Taking the volume of liquid water as negligible (100 mL = 0.1 L), ΔV = 203.8 L

∴ w = −P_ext ΔV = −1 atm × 203.8 L atm = −203.8 L atm

= −203.8 × 101.3 J = −20.6 kJ