Fe2+ + MnO4 -> Fe3+ + Mn2+
NO3- + S2-+ -> S+ NO
NH3+NO2 -> N2+H2O
Assign oxidation numbers to each element
Write half reactions for each
Balance these half reactions
For the given reactions:
1) Fe2+ + MnO4- -> Fe3+ + Mn2+
Oxidation numbers:
Fe2+ --> +2
MnO4- --> +7
Half-reactions:
Oxidation half-reaction: Fe2+ --> Fe3+
Reduction half-reaction: MnO4- --> Mn2+
2) NO3- + S2- -> S + NO
Oxidation numbers:
NO3- --> -1
S2- --> -2
Half-reactions:
Oxidation half-reaction: S2- --> S
Reduction half-reaction: NO3- --> NO
3) NH3 + NO2- -> N2 + H2O
Oxidation numbers:
NH3 --> -3
NO2- --> +3
Half-reactions:
Oxidation half-reaction: NH3 --> N2
Reduction half-reaction: NO2- --> H2O
Balancing of the half-reactions:
1) Fe2+ --> Fe3+ (oxidation)
Fe2+ -> Fe3+
To balance the charges, we need to add one electron on the left side:
Fe2+ + 1e- -> Fe3+
2) MnO4- --> Mn2+ (reduction)
MnO4- -> Mn2+
To balance the charges, we need to add five electrons on the left side:
MnO4- + 5e- -> Mn2+
3) S2- --> S (oxidation)
S2- -> S
To balance the charges, we need to add two electrons on the right side:
S2- -> S + 2e-
4) NO3- --> NO (reduction)
NO3- -> NO
To balance the charges, we need to add three electrons on the left side:
NO3- + 3e- -> NO
5) NH3 --> N2 (oxidation)
NH3 -> N2
To balance the charges, we need to add three electrons on the right side:
NH3 -> N2 + 3e-
6) NO2- --> H2O (reduction)
NO2- -> H2O
To balance the charges, we need to add two electrons on the left side:
NO2- + 2e- -> H2O