Sublimation
Sublimation is a phase transition in which a solid changes directly into a gas without passing through the liquid state.
Phase diagram: A graph showing the stable phases of a substance across conditions such as temperature and pressure. Its pressure–temperature boundaries show where sublimation is possible.
Freeze-drying: A preservation process that removes frozen water by reducing pressure so ice sublimes. It uses sublimation to dry foods, medicines, and biological samples.
Carbon dioxide: A colorless gas composed of one carbon atom and two oxygen atoms, also available as a solid. At atmospheric pressure, its solid form sublimes rather than melting.
Melting: The phase transition in which a solid becomes a liquid. Unlike sublimation, melting passes through the liquid state.
Triple point: The unique temperature and pressure at which a substance’s solid, liquid, and gas phases coexist in equilibrium. Below this pressure, heating a solid cannot produce a stable liquid phase.
Lyophilization: A dehydration technique that freezes a material and removes ice under vacuum by sublimation. This term names the controlled industrial and laboratory form of freeze-drying.
Iodine: A chemical element whose dark, lustrous solid can produce a violet vapor when heated. Its conspicuous vapor makes sublimation easy to demonstrate.
Evaporation: The conversion of liquid into gas from a liquid’s surface. It starts from a liquid, whereas sublimation starts from a solid.
Vapor pressure: The pressure exerted by a vapor in equilibrium with its condensed phase at a given temperature. A solid’s vapor pressure determines its tendency to sublime.
Chemical purification: The separation of desired substances from impurities using differences in their physical or chemical properties. Sublimation can separate volatile solids from nonvolatile contaminants.