Why is an external emf of more than 2.2V required for the extraction of Cl2 from brine?
2Cl– (aq) + 2H2O(l) → 2OH– (aq) + H2(g) + Cl2(g)
The ΔGᶱ for this reaction is +422kJmol-1.
Using the formula, ΔGᶱ = -nFE°
E° = 422 x 103/2×96500
we get = -2.2V
For the reaction to take place the external voltage should be greater than 2.2V otherwise the reaction will not happen.