What is sublimation?
Sublimation can be defined as the transition of a substance from solid phase to gaseous phase without changing into liquid phase. This process is an endothermic phase transition that occurs at a temperature and pressure below the triple point of the substance. Desublimation or deposition is the reverse of this process in which a gas is directly converted into solid state.
Elements and compounds mainly possess three different states at various temperatures. The transition from solid state to gaseous state requires transition of solid state to liquid state and liquid state to gaseous state. If solids possess sufficient vapour pressure at a particular temperature then they can directly sublime into air. Solids which have a high pressure at their triple point show sublimation. Triple point is the point at which the pressure and temperature of the substance is such that it can exist in all three states of matter simultaneously. The triple point is a characteristic point of a substance. There are various examples of sublimation which are experienced by us in our everyday life.
Best example of sublimation is dry ice which is a frozen form of carbon dioxide. When dry ice gets exposed to air, dry ice directly changes its phase from solid state to gaseous state which is visible as fog. Frozen carbon dioxide in its gaseous state is more stable than in its solid state. Another well-known example of sublimation is naphthalene which is a organic compound. Naphthalene is usually found in pesticides such as mothball. This organic compound sublimes due to the presence of non-polar molecules that are held by Van Der Waals intermolecular forces. At a temperature of 176F naphthalene sublimes to form vapours. It desublimates at cool surfaces to form needle-like crystals. Sublimation finds practical application in forensic sciences. Dye-sublimation printers help in rendering digital pictures in a detailed and realistic fashion which helps in the analysis of substances. Chemists usually prefer sublimation as purification method to purify volatile compounds.
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