Question

Magnesium ions and sulfate ions have the following reduction and oxidation reactions and potentials:

Mg2+(aq) + 2e– →Mg(s)	Eo = –1.18 V
2SO42–(aq)→S2O82–(aq) + 2e–	Eo = –2.05 V

Why did neither of these half-reactions occur when the magnesium sulfate solution was electrolyzed?

Answer 1

A reaction will occur only if standard free energy ,∆G^o is negative.

In both the given equations standard reduction ,E^{​​​​​​o} value is negative and we know that ∆G^o =- nFE^{​​​​o}

So both the reaction have positive value of ∆G^o

That's why neither of these two half reactions occur.