What is the process called when a gas directly changes into a solid?

The process in which a gas transitions directly into a solid is referred to as deposition. This phase change occurs without the intermediate state of liquid, making it a unique transformation. An example of deposition is the formation of frost on surfaces when water vapor in the air freezes directly into ice without becoming liquid water first.

Understanding deposition is important because it has distinct characteristics and contrasts with other phase changes. For instance, condensation is the process where a gas becomes a liquid, sublimation is the direct transition from solid to gas, and evaporation refers to the transition of a liquid into a gas. Each of these processes has its specific conditions and thermodynamic implications, highlighting the diversity of phase changes in physical chemistry.