Describe in brief about sublimation.

Que.: Describe in brief about sublimation.

Ans.:

Sublimation:

Sublimation is the transition of a substance directly from the solid to the gas phase, without passing through the intermediate liquid phase.

It 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).

The term sublimation refers to a physical change of state and is not used to describe the transformation of a solid to a gas in a chemical reaction. For example, the dissociation on heating of solid ammonium chloride into hydrogen chloride and ammonia is not sublimation but a chemical reaction.

Sublimation is caused by the absorption of heat which provides enough energy for some molecules to overcome the attractive forces of their neighbours and escape into the vapour phase.

Since the process requires additional energy, it is an endothermic change.
The enthalpy of sublimation (also called heat of sublimation) can be calculated by adding the enthalpy of fusion and the enthalpy of vaporization.

Que.: Describe in brief about sublimation.