What process is occurring when a solid changes directly to a gas?

The process in which a solid changes directly to a gas is known as sublimation. This occurs when the molecules in a solid gain enough energy to overcome the intermolecular forces holding them together, allowing them to transition directly into the gas phase without passing through the liquid state. Sublimation is commonly observed in substances such as dry ice (solid carbon dioxide), which sublimates at room temperature, turning directly into carbon dioxide gas.

In contrast, condensation refers to the transition from gas to liquid, while evaporation is the process by which a liquid turns into a gas. Melting is the process where a solid turns into a liquid. Understanding these distinct phases of matter and their transitions is fundamental in the study of physical chemistry, highlighting the unique characteristics associated with each state.