Sublimation (Phase Transition)
What is Sublimation?
Sublimation is the method by which the material changes from the frozen solid to the gas without going through the intermediate liquid state. It is an endothermic process at pressure and temperature. It is lower than the triple point of substance with its transition phase that refers to the lower pressure at which the substance would remain the same as a liquid form. We may transform the sublimation as transforming material from the solid phase to the gaseous phase without changing into the liquid phase. This approach is an endothermic phase transition at a temperature and pressure below the substance's triple point. The opposite of this phase in which a gas is directly converted to solid-state is de-sublimation or deposition.
Examples of Sublimation
Various examples of sublimation are as follows:
Dry ice is the essential example of sublimation, a frozen form of carbon dioxide. If dry ice is exposed to air, dry ice changes its phase immediately from a solid-state to a gaseous state that is recognizable as fog. In its gaseous state, frozen carbon dioxide is more stable than its solid-state.
Water, ice, and snow are examples of sublime, but these move slowly at temperatures below the freezing and melting point line at 0 C and partial pressure less than the triple point pressure of 612 Pa. During freeze-drying, the substance to be dehydrated is frozen, and the water is enabled to sublimate in lower pressure or vacuum. Sunshine acting directly upon on top layers of the snow causes the loss of snow from a snowfield during a cold period. Sublimation and erosive wear of glacier ice is also part of the process.
Naphthalene is an organic compound, which is another well-known example of sublimation. Naphthalene is commonly present in mothball-like pesticides. The mothballs and naphthalene balls may easily sublime because of the presence of the non-polar molecules held together by the Van Der Waals intermolecular forces. Naphthalene sublimates to form vapors at a temperature of 176F. It de-sublimates to form needle-like crystals on cool surfaces.
Iodine produces soft-heating fumes, but it is above the triple stage. At atmospheric pressure, liquid iodine can be obtained by keeping the temperature above iodine's melting point. Iodine vapor can expose latent fingerprints on paper in forensic science. At high temperatures, Arsenic can also sublimate.
In forensic sciences, sublimation finds practical use. Dye-sublimation printers help create digital images in a detailed and practical way that helps analyze substances. Chemists typically prefer sublimation as a purification process for the purification of volatile compounds.