When heat is added to liquid water, the molecules gain energy and move faster, breaking the hydrogen bonds between them. As a result, the liquid water evaporates and turns into a gas, water vapour. The boiling point of water is the temperature at which the vapour pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapour. The boiling point of water at sea level is 100 degrees Celsius (212 degrees Fahrenheit).

Here is a more detailed explanation of the process:

1. Kinetic energy increases: When heat is added to liquid water, the molecules gain kinetic energy and move faster. This increased kinetic energy causes the molecules to collide with each other more frequently and with greater force.

2. Breaking hydrogen bonds: The water molecules are held together by hydrogen bonds, which are intermolecular forces that form between a hydrogen atom and a highly electronegative atom such as oxygen or nitrogen. As the molecules move faster and collide with each other more frequently, the hydrogen bonds between them begin to break.

3. Escape from the liquid: As more and more hydrogen bonds are broken, the molecules are able to escape from the liquid and into the gas phase. This process is called evaporation.

4. Boiling: The boiling point of water is the temperature at which the vapour pressure of the liquid equals the pressure surrounding the liquid. At this temperature, the water molecules have enough energy to overcome the atmospheric pressure and escape from the liquid in large numbers. The water is said to be boiling.