All the energy released from the reaction X→Y, ΔrG∘=−193 kJ.mol−1 is used for oxidizing M+ as M+→M3++2e−,E∘=−0.25V.
Under standard conditions, the number of moles of M+ oxidized when one mole of X is converted to Y is:
[F=96500 Cmol−1]
For the reaction M+→M3++2e−,, the standard Gibbs free energy change is
ΔG0=−nFE0=−2×96500×(−0.25)=48250J/mol=48.25kJ/mol
The number of moles of M+ oxidized (when 1 mol of X is converted to Y) is 193kJ/mol48.25kJ/mol=4