<P> Vapourization (or vapourisation) 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 . </P> <P> Evaporation is a phase transition from the liquid phase to vapor (a state of substance below critical temperature) 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 . For example, due to constantly decreasing or negative pressures, vapor pumped out of a solution will leave behind a cryogenic liquid . </P> <P> Boiling is also a phase transition from the liquid phase to gas phase, but boiling is the formation of vapor as bubbles of vapor below the surface of the liquid . Boiling occurs when the equilibrium vapor pressure of the substance is greater than or equal to the environmental pressure . The temperature at which boiling occurs is the boiling temperature, or boiling point . The boiling point varies with the pressure of the environment . </P>

When is a liquid said to be not in a boiling or vaporized state