14.2 Balancing Oxidation-Reduction Reactions

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How to Balance Redox Reactions

Half-Reaction Method for Balancing Redox Reactions
1) Split into half reactions. 2) Balance all elements except oxygen and hydrogen. 3) Balance oxygen by adding H₂O. 4) Balance hydrogen by adding H⁺. 5) Balance the charge by adding electrons. 6) Mulitply half reactions by factors to make the number of electrons the same. 7) Combine half reactions canceling anything that shows up on both sides of the reaction. 8) Conditional: If balancing in base add the same number of OH- to both sides as H+ present. On the side with the H⁺ the H⁺/OH^- combine to form H₂O. 9) Cancel any excess H₂O that now shows up on both sides of the reaction (if necessary).

Half-Reaction Method for Balancing Redox Reactions

1) Split into half reactions.
2) Balance all elements except oxygen and hydrogen.
3) Balance oxygen by adding H₂O.
4) Balance hydrogen by adding H⁺.
5) Balance the charge by adding electrons.
6) Mulitply half reactions by factors to make the number of electrons the same.
7) Combine half reactions canceling anything that shows up on both sides of the reaction.
8) Conditional: If balancing in base add the same number of OH- to both sides as H+ present.
On the side with the H⁺ the H⁺/OH^- combine to form H₂O.
9) Cancel any excess H₂O that now shows up on both sides of the reaction (if necessary).

Balance the following:
Ag⁺(aq) + Al(s) → Ag(s) + Al³⁺(aq)

MnO₄^-(aq) + I^-(aq) → Mn²⁺(aq) + I₂(s)

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