Redox reactions involve oxidation and reduction occurring simultaneously.

Oxidation is the loss of electrons

Reduction is the gain of electrons

As stated previously, these two reactions cannot occur in isolation.

The two equations are added to provide the reaction equation:

In terms of oxidation number:

• For the oxidation: there has been an increase of +2
• For the reduction: there has been an increase of -2

Displacement reactions occur if for example you place a more reactive metal in a solution containing ions of a less reactive metal.

For example:

If we now compare this with the following reaction:

We see that metals can be both oxidised and reduced, we write:

The &ruldhar; sign shows that the reaction can go both ways. It is the sign for dynamic equilibrium.

If a piece of metal is placed into a solution of its own ions, two occurrences may appear.

Metal atoms may leave the solid and become metal ions in solution:

Oxidation

In this case the electrons that are released stay on the surface of the solid, which causes it to gain a negative charge.

Or, metal ions in solution may become metal atoms on the surface of the solid.

Reduction

In this case, electrons are attracted into the solution.