Redox reactions

Oxidation is the loss of electrons by a reactant.

When a metal element is reacting to form a compound then it is being oxidised.

For example:

\[Mg(s) + O_2^{}(g) \to MgO(s)\]

The metal atoms are losing electrons to form an ion. They are being oxidised.

\[Mg(s) \to Mg_{}^{2 + }(aq) + 2e_{}^ - \]

This is known as an ion-electron equation.

Reduction is the opposite of oxidation. It is the gain of electrons.

Compounds reacting that result in metal elements being formed are examples of reduction reactions.

For example:

\[Cu_{}^{2 + }(aq) + 2e_{}^ - \to Cu(s)\]

The metal ions are gaining electrons to form atoms of the element. They are being reduced.

Oil Rig

An oil rig for the pneumonic Oil Is Loss Reduction Is Gain

Redox reactions are reactions where both oxidation and reduction are taking place.

Displacement reactions are examples of redox reactions as one species is being oxidised (losing electrons) while the other is being reduced (gaining electrons).

For example, if magnesium was added to copper sulphate solution, the magnesium metal would be oxidised, while the copper ions were being reduced.

\(Cu(s) \to Cu_{}^{2 + }(aq) + 2e_{}^ - \) oxidation reaction

\(2Ag_{}^ + (aq) + 2e_{}^ - \to 2Ag(s)\) reduction reaction

\(Cu(s) + 2Ag_{}^ + (aq) \to Cu_{}^{2 + }(aq) + 2Ag(s)\) redox reaction

Another example of a redox reaction is the electrolysis of an ionic compound. During electrolysis, negative ions lose electrons at the positive electrode (oxidation) and positive ions gain electrons at the negative electrode (reduction).

Both fuel cells and rechargeable batteries are examples of energy sources that power objects through redox reactions.