redox reaction

A redox reaction is a reaction involving reduction and oxidation half-reactions.

To balance a simple redox reaction

1. Split the redox reaction into reduction and oxidation half-reactions.
2. The oxidation reaction has free electrons on the product side. The number of electrons produced should be equal to how much the reducing agent’s oxidation state increased.
3. The reduction reaction has free electrons on the reactant side. The number of electrons absorbed should be equal to how much the oxidizing agent’s oxidation state decreased.
4. Balance and add the half-reactions so that free electrons on both sides cancel out.

To balance acid/base redox reaction (oxygens / hydrogens involved)

1. Split the redox reaction into reduction and oxidation half-reactions.
2. Balance the half reactions while disregarding the oxygens and hydrogens in the species.
3. Add $\mathrm{H}{}_2\mathrm{O}$ to balance oxygens in both half-reactions.
4. Add $\mathrm{H}{}^{+}$ to balance hydrogens in the both half-reactions.
5. Balance the charge of each half-reaction with $\mathrm{e}{}^{-}$.
6. Balance and add the half-reactions so that free electrons on both sides cancel out.