1. (a) Balance the equation below under acidic conditions and indicate the number of electrons transferred in the oxidative and reductive half-reactions :

(MnO₄^- + 4H⁺ + 3e^- <==> MnO₂ + 2H₂O) x 2

(NO₂^- + H₂O <==> NO₃^- + 2H⁺ + 2e^-) x 3

2MnO₄^- + 2H⁺ + 3NO₂^- <==> 2MnO₂ + 3NO₃^- + H₂O

2. Given the standard (acidic) reduction potentials:

MnO₄^- / MnO₂ = + 1.70 V and NO₃^- / NO₂^- = +0.94 V

Spontaneous reactions make up a galvanic cell so E^o_cell must be positive so that DG will be negative.

DG = -nFE = -6*96.5 kJmol^-1V^-1*0.76V = -440 kJ So yes the rxn will make a galvanic cell.

(c) Explain (without a calculation) in what way an increase of pH from pH 1 to pH 12 will affect the value of E_rxn.

The concentration of hydronium ions will decrease in the basic environment, which will push the reaction in part ‘a’ towards the reactants, decreasing the reaction potential as described by the Nernst equation.