vaporisation

Vaporisation is the process by which a substance changes from a liquid to a gaseous state. It includes two main mechanisms: evaporation and boiling. Evaporation is a surface process that can occur at any temperature below a liquid’s boiling point and is influenced by temperature, surface area, and air movement. Boiling is a bulk process that occurs when the liquid reaches its boiling point and forms vapor bubbles within the liquid. Sublimation, the transition from solid to gas, is sometimes described as a form of vaporisation.

The rate and conditions of vaporisation are governed by vapor pressure and ambient pressure. When a liquid’s vapor pressure equals the surrounding pressure, boiling begins. Lower ambient pressure lowers the boiling point, while higher pressure raises it. At sufficiently high pressure and temperature, a liquid can approach a supercritical state, where liquid and gas properties converge.

Vaporisation requires energy, in the form of the latent heat of vaporization, the amount needed to transform one mole of liquid to gas at its boiling point. The Clausius–Clapeyron relation relates vapor pressure to temperature and is used to model vaporisation under changing conditions.

Industrial and practical relevance includes distillation and drying processes, steam generation, spray drying, and deposition techniques such as vapor deposition. Evaporation also drives natural processes in the water cycle and contributes to cooling of surfaces and bodies.