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

Explanation

The decomposition reactions are called the opposite of combination reactions because in a combination reaction two or more substances combine to form single substance whereas in a decomposition reaction, a single substance splits up to form two or more simple substances.
(a) When hydrogen burns in oxygen, it forms water: ltbr `2H_(2)(g)+O_(2)(g)to2H_(2)O(l)`
In this reaction two substances hydrogen and oxygen combine to form a signe substance water so this is a combination reaction.
(b) WHen acidified water is electrolysed hydrogen and oxygen are formed:
`2H_(2)O(l) overset("Electricity")(to)2H_(2)(g)+O_(2)(g)`
Here a single substance water breaks upinto two simple substances hydrogen and oxygen. So, this is a decomposition reaction. We can see from the above examples that a decomposition reaction is opposite of a combination reaction.