What does water change into when it is heated and reaches its boiling point?

When water is heated and reaches its boiling point, it changes into water vapour or steam. This process is called boiling, which is a physical change where water changes from the liquid state to the gaseous state.

At standard atmospheric pressure, water boils at 100°C. When heat energy is supplied, water molecules gain energy and start moving faster. Once they have enough energy to overcome the forces holding them together in the liquid state, they escape into the air as water vapour.

This change does not create a new substance because the chemical composition of water (H₂O) remains the same. The process can also be reversed when water vapour cools and changes back into liquid water through condensation.

Understanding this transformation helps students learn about states of matter, heating effects, and changes that occur in everyday life.