Sublimation (phase transition)

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Dry Ice Vapor (17490553041)

Sublimation reaction of naphthalene

Crystal-like sublimated naphthalene

Sublimation (phase transition) is a process in which a solid changes directly into a gas without passing through an intermediate liquid phase. This endothermic phase transition occurs under certain temperature and pressure conditions and is an example of a phase transition, a fundamental concept in the field of thermodynamics. Sublimation is the reverse process of deposition, where a gas transforms directly into a solid.

Overview

Sublimation is observed in substances with strong molecular bonds in the solid phase that weaken sufficiently at certain temperatures to transition directly into the gas phase. This process requires energy, typically in the form of heat, to overcome the forces holding the molecules in the solid state. The energy required for sublimation is defined as the enthalpy of sublimation, which is a specific type of latent heat.

Conditions for Sublimation

The conditions under which sublimation occurs depend on the substance's pressure and temperature. The phase diagram of a substance can illustrate the conditions for sublimation. At pressures below the substance's triple point, where solid, liquid, and gas phases coexist, sublimation can occur at temperatures below the melting point of the solid.

Examples

A common example of sublimation is the transition of dry ice (solid carbon dioxide) into carbon dioxide gas at temperatures above -78.5°C (-109.3°F) at atmospheric pressure. Another example is the sublimation of iodine at room temperature, where it forms a purple gas.

Applications

Sublimation has various applications in both natural and industrial processes. In nature, sublimation is responsible for the erosion of glaciers and the formation of ice crystals in the atmosphere. Industrially, sublimation is used in the freeze-drying process to preserve food and pharmaceuticals, in the purification of substances, and in the manufacturing of certain types of semiconductor devices and optical fibers.

Sublimation in Everyday Life

In everyday life, sublimation can be observed in the disappearance of snow and ice on a cold, dry day, bypassing the liquid phase. This process is also exploited in air fresheners that release fragrance molecules into the air.

See Also

• Phase diagram
• Latent heat
• Deposition (phase transition)
• Freeze-drying

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