What is the process of a solid changing directly into a gas called?

The process of a solid changing directly into a gas is known as sublimation. This phase transition occurs without passing through the liquid state. A common example of sublimation is the way dry ice (solid carbon dioxide) turns directly into carbon dioxide gas when exposed to air at room temperature.

In sublimation, the molecules of the solid gain enough energy to overcome the forces holding them in a solid structure and escape into the gaseous state. This is distinct from other processes such as melting, where a solid becomes a liquid, and vaporization, which involves a liquid turning into a gas. Condensation is the opposite process, where a gas cools and transitions back into a liquid. Understanding sublimation is important in various fields, including chemistry and environmental science, as it plays a significant role in processes like freeze-drying and the behavior of substances under different temperature and pressure conditions.