Half Equations

Show separate oxidation and reduction reactions within one redox reaction

Balanced in terms of the species (particles) and the charges

Use this method -

1. Balance all particles EXCEPT oxygen + hydrogen

2. Balance oxygen using H2O

3. Balance hydrogen using H+ ions

4. Balance charges using e- (electrons)

If the oxidation state of the species increases then it’s an oxidation reaction:

• Electrons are on the right hand (product) side

• Electrons are being lost

If the oxidation state of the species decreases then it’s a reduction reaction:

• Electrons are on the left hand (reactant) side

• Electrons are being gained

Half equations can be combined to form overall redox reaction - which is why number of electrons must be the same for both half equations

An oxidising agent must be reduced itself to oxidise others - it will gain electrons