Boiling Definition in Chemistry

Chemistry Glossary Definition of Boiling

A classic example of boiling is boiling water.
A classic example of boiling is boiling water. Dorling Kindersley / Getty Images

Boiling is defined as a phase transition from the liquid state to the gas state, usually occurring when a liquid is heated to its boiling point. At the boiling point, the vapor pressure of the liquid is the same as the external pressure acting upon its surface.

Also Known As: Two other words for boiling are ebullition and vaporization.

Boiling Example

A good example of boiling is seen when water is heated until it forms steam. The boiling point of fresh water at sea level is 212°F (100°C). The bubbles that form in the water contain the vapor phase of water, which is steam. The bubbles expand as they get closer to the surface because there is less pressure acting upon them.

Boiling Versus Evaporation

In the process of evaporation, particles may transition from the liquid phase to the gas phase. However, boiling and evaporation do not mean the same thing. Boiling occurs throughout the volume of a liquid, while evaporation only occurs at the surface interface between the liquid and its surroundings. The bubbles that form during boiling do not form during evaporation. In evaporation, the liquid molecules have different kinetic energy values from one another.