Sublimationa

Sublimation is a phase transition process where a substance changes directly from a solid to a gas without passing through the liquid phase. This occurs when the vapor pressure of the solid equals the surrounding atmospheric pressure. Several factors influence sublimation, including temperature and pressure. When the temperature of a solid increases, its molecules gain kinetic energy and can overcome the intermolecular forces holding them in a fixed lattice structure. If the temperature is high enough and the surrounding pressure is sufficiently low, these molecules can escape directly into the gaseous state.

A common example of sublimation is dry ice, which is solid carbon dioxide. At atmospheric pressure, dry ice does not melt into liquid carbon dioxide; instead, it transforms directly into gaseous carbon dioxide. This is why dry ice appears to "smoke" or vaporize. Another everyday example is the gradual disappearance of ice cubes in a freezer over time, even if the freezer is cold enough to prevent melting. This occurs because water molecules can escape from the solid ice directly into the gaseous water vapor in the air. The reverse process, where a gas changes directly into a solid, is called deposition or desublimation.