Why are decomposition reactions called the opposite of combination reactions ? Write equations for these reactions.

Explanation

Decomposition reactions are those in which a compound breaks down to form two or more substances. These reactions require a source of energy to proceed. Thus, they are the exact opposite of combination reactions in which two or more substances combine to give a new substance with the release of energy.
Eg. Decomposition Reaction :
`CaCO_3(s)toCaO(s)+CO_2(g)` ln Combination reactions, two or more substances combine to give a new substance with the release of energy.
Eg : Combination Reaction `CaO(s)+H_2O(l)toCa(OH)_2(aq)`