Water boiling is not a chemical reaction; it is a physical change. When water boils, it changes from a liquid state to a gaseous state, but the chemical composition of the water remains the same. The molecules of water (H2O) do not break down into hydrogen and oxygen atoms during boiling.
In a chemical reaction, the substances involved undergo a change in their chemical composition, resulting in the formation of new substances with different properties. For example, when hydrogen gas (H2) reacts with oxygen gas (O2), they form water (H2O), which is a chemical reaction.
Boiling water, on the other hand, is a phase change. The heat energy added to the water causes the water molecules to move faster and overcome the intermolecular forces holding them together in the liquid state. This results in the formation of water vapor, but the water molecules themselves remain unchanged.
In summary, boiling water is a physical change because it involves a change in the state of matter without altering the chemical composition of the water.