Task 5.1e

Which of the following are spontaneous disproportionation reactions?
(a) 3MnO₄^2-(aq) 4H⁺(aq) ---> MnO₂(s) + 2MnO₄^-(aq) + 2H₂O(l)
(b) 2MnO₄^-(aq) + 16H⁺(aq) + 5C₂O₄^2-(aq) ---> 2Mn²⁺(aq) + 8H₂O(l) + 10CO₂(g)
(c) 3HNO₂(aq) ----> HNO₃(aq) + 2NO(g) + H₂O(l)

CO₂ + H⁺ +e^- ---> 1/2 H₂C₂O₄  E^o = +0.49V
MnO₄^-(aq) +e^-  ---> MnO₄^2-(aq) E^o = +0.60V
MnO₄^-(aq) +8H⁺ + 5e^-  ---> Mn²⁺(aq) + 4H2O(l) E^o = +0.60V
MnO₄^2-(aq) 4H⁺(aq) + 2e^- = MnO₂(s)  + 2H₂O(l) E^o = +1.55V
NO₃^-(aq) + 3H⁺(aq) +2e^- = HNO₂(aq) + H₂O(l)  E^o = +0.94V
HNO₂(aq) + H⁺(aq) +e^- = NO(g) + H₂O(l)              E^o = +0.99V

Answers: (a) disproportionation, (b) not disproportionation, (c) disproportionation