<P> Sublimation is the phase transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase . Sublimation is an endothermic process that occurs at temperatures and pressures below a substance's triple point in its phase diagram, which corresponds to the lowest pressure at which the substance can exist as a liquid . The reverse process of sublimation is deposition or desublimation, in which a substance passes directly from a gas to a solid phase . Sublimation has also been used as a generic term to describe a solid - to - gas transition (sublimation) followed by a gas - to - solid transition (deposition). </P> <P> At normal pressures, most chemical compounds and elements possess three different states at different temperatures . In these cases, the transition from the solid to the gaseous state requires an intermediate liquid state . The pressure referred to is the partial pressure of the substance, not the total (e.g. atmospheric) pressure of the entire system . So, all solids that possess an appreciable vapour pressure at a certain temperature usually can sublime in air (e.g. water ice just below 0 ° C). For some substances, such as carbon and arsenic, sublimation is much easier than evaporation from the melt, because the pressure of their triple point is very high, and it is difficult to obtain them as liquids . </P>

Where does sublimation occur on a phase diagram