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

Explanation

The decomposition reactions are those in which a compound breaks up into two or more simpler substances. On the other hand, combination reactions are those in which two or more substances combine to form a single substance.
Thus, the decomposition reactions are opposite of the combination reactions.
For example, decomposition reactions are :
`CaCO_(3(s))toCaO_((s))+CO_(2(g))`
`2H_(2)O_((l))overset("Electricity")to2H_(2(g))+O_(2(g))`
For example, combination reactions are :
`2H_(2(g))+O_(2(g))to2H_(2)O_((l))`
`NH_(3(g))+HCl_((g))toNH_(4)Cl_((s))`