Question

When hydrogen in oxygen, water is formed; when electricity is passed through water, hydrogen and oxygen are given out. Name the type of chemical changes involved in the two cases.

Answer 1

Both are chemical changes as they are irreversible and chemical composition gets changed.

The formation of water is a combination reaction.

$2H_2$ + $O_2$ $\to$ $2H_{2}O$

The electrolysis of water to give hydrogen and oxygen is a decomposition reaction.

$2H_{2}O$ $\to$ $2H_2$ + $O_2$