What is the term for when a solid changes directly to a gaseous state?

The term for when a solid changes directly to a gaseous state is sublimation. This process occurs without going through the liquid phase and is a unique transition that can happen under certain conditions of temperature and pressure. A common example of sublimation is dry ice (solid carbon dioxide); it transitions directly into carbon dioxide gas without becoming liquid first.

In contrast, fusion refers to the process where a solid melts into a liquid. Evaporation is the process of converting a liquid into a gas, typically occurring at the surface of the liquid and at a temperature below its boiling point. The term "smoke" does not relate to a phase change; rather, it refers to the visible gas, primarily consisting of small particles, produced by combustion or pyrolysis. Understanding these terms helps clarify the distinctions between different phase transitions and states of matter.