Decomposition is a type of chemical reaction and it may be defined as the reaction in which a single compound splits into two or more simple substances under suitable conditions. It is just the opposite of the combination reaction. The digestion of food in our body is accompanied by a number of decomposition reactions. There are three types of decomposition reactions : Thermal, Electrolytic and Photo decomposition reactions. Thermal decomposition is a chemical reaction where a single substance breaks into two or more simple substances when heated. Electrolytic decomposition may result when electric current is passed through an aqueous solution of a compound. Photo decomposition is a chemical reaction in which a substance is broken down into simple substances by exposure to light (photons).
This video explains the decomposition reaction of hydrated ferrous sulphate.