汽化是指物质状态从液体或固体向气体转换的一种相变，过程进行中需要吸热。汽化有三种型式，蒸发、沸腾和升华。蒸发是只在液体表面发生，并且液体温度低于某一压力时的沸点。而沸腾是一种剧烈的汽化过程，在液体的表面与内部同时进行。仅在液体达到沸点后并可以继续吸热的条件下才能发生。

Vaporisation (or vaporization) of an element or compound is a phase transition from the liquid phase to vapor There are two types of vaporization: evaporation and boiling. Evaporation is a surface phenomenon, whereas boiling is a bulk phenomenon.

Evaporation is a phase transition from the liquid phase to vapor (a state of substance below critical temperature and critical pressure) that occurs at temperatures below the boiling temperature at a given pressure. Evaporation occurs on the surface. Evaporation only occurs when the partial pressure of vapor of a substance is less than the equilibrium vapor pressure.