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

Explanation

Combination reaction in which two or more substances combine under suitable conditions to form a new substance. For example,
`2H_(2)(g) + O_(2)(g) overset("Heat")to 2H_(2)O(g)`
`H_(2)(g) + Cl_(2)(g) overset("Sun light")to 2HCl(g)`
A decomposition reaction may be defined as the reaction in which a single substances decomposes or splits into two or more substances under suitable conditions.
For example,
`CaCO_(3)(s)overset("Heat")to CaO(s) + CO_(2)(g)`
`2Pb(NO_(3))_(2) (s) overset("Heat")to 2PbO(s) + 4NO_(2)(g) + O_(2)(g)`
It may be concluded that a certain substance is formed or synthesised in combination reaction and it breaks or splits in decomposition reaction, Therefore, the two reactions oppose each other.