Redox
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
We can write this overall reaction as two half-reactions: an oxidation reaction:
- H2 → 2H+ + 2e-
and a reduction reaction:
- F2 + 2e- → 2F-
Elements always have an oxidation number of zero. In the first half reaction hydrogen is oxidized from an oxidation number of zero to an oxidation number of +1. In the second half reaction fluorine is reduced from an oxidation number of zero to an oxidation number of -1
When adding the reactions together the electrons cancel and the ions combine to form hydrogen fluoride:
- 2H+ +2F- → 2HF
As another example, consider the oxidation of iron(II) to iron(III):
- Fe2+ --> Fe3+ + e
and the reduction of
hydrogen peroxide:
- H2O2 + 2 e --> 2 OH-
The two processes occur together in the following redox reaction:
- 2Fe2+ + H2O2 + 2H+ --> 2Fe3+ + 2H2O
See also: electrochemistry