In chemistry, a redox reaction is a chemical reaction which consists of an oxidation reaction and a reduction reaction. That is one species gains electrons -- it is reduced -- at the cost of the other, which is oxidized. In a redox reaction the oxidation numbers of the two species are changing.
A good example is the reaction between hydrogen and fluorine:
- H2 + F2 → 2HF
- H2 → 2H+ + 2e-
- F2 + 2e- → 2F-
When adding the reactions together the electrons cancel and the ions combine to form hydrogen fluoride:
- 2H+ +2F- → 2HF
- Fe2+ --> Fe3+ + e
- H2O2 + 2 e --> 2 OH-
- 2Fe2+ + H2O2 + 2H+ --> 2Fe3+ + 2H2O