Question

Write the two half-reactions involved in the disproportionation of hydrogen peroxide to water and diatomic oxygen. Balance the equation . Calcuate E^o for the overall reaction.

Answer 1

When in a redox reactions, one substance is both oxidized and reduced in the same reaction then those reactions are called disproportionation reactions.

Decomposition of hydrogen peroxide to water and oxygen is an ideal example of disproportionation reaction where H₂O₂ is at a time is oxidized to oxygen as well as reduced to water.

Oxidation : H₂⁺¹O₂^-1 O₂⁰ + 2H⁺  + 2e E⁰_ox = - 0.68 V

Reduction : H₂⁺¹O₂^-1 + 2e + 2H⁺ 2H₂O^-2   E⁰_red= 1.77 V

Total balanced reaction :2H₂O₂ 2H₂O + O₂ where E^o _Total = E⁰_ox + E⁰_red =   (- 0.68 + 1.77 ) V = 1.09 V

Since E^o _Total is a large positive value so this disprotionation reaction is thermodynamically strongly favored.