Oxidation and Reduction: Introduction to redox processes

Oxidation is the process of a substance gaining oxygen in a chemical reaction. For example, magnesium burns in oxygen, with the equation for this reaction being:

2Mg(s) + O2-->2MgO(s)

This shows that magnesium has been oxidised as it gains oxygen to become magnesium oxide. 

There is also a reverse process for oxidation: yes, the loss of oxygen!! Such a process is called reduction. A substance that loses oxygen in a reaction is said to be reduced. Another such example would be zinc reacting with copper (II) oxide. The equation for the reaction is :

Zn(s) + CuO (s) --> ZnO(s) + Cu(s)

In the reaction, the copper (II) oxide reacts and loses oxygen, therefore being called "reduced".

Such two processes usually takes place together! In the reaction for zinc reacting with copper (II) oxide, 

the zinc gets oxidised whilte the copper (II) oxide loses oxygen. The name for such reactions are called redox reactions.