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

Explanation

In decomposition reaction, a single compound splits up into two or more simple compounds.
Example : Decomposition of calcium carbonate
`CaCO_(3)(s)overset("sunlight")(to)CaO(s)+CO_(2)(g)`
In combination reaction, two or more elements or compounds combine to form a single compound.
Example : Nitrogen and hydrogen combine to form ammonia
`N_(2)(g)+3H_(2)(g)to2NH_(3)(g)`