The process of changing from a solid to a gas is called sublimation. The opposite process, changing from a gas to a solid, is called deposition.

Here's a breakdown:

Sublimation:

* Definition: A substance transitions directly from its solid state to its gaseous state without passing through the liquid state.

* Example: Dry ice (solid carbon dioxide) sublimates at room temperature, turning directly into carbon dioxide gas.

Deposition:

* Definition: A substance transitions directly from its gaseous state to its solid state without passing through the liquid state.

* Example: Frost forming on a cold window pane is a result of water vapor in the air depositing directly onto the surface as ice crystals.

Key Points:

* Both sublimation and deposition are physical changes – they do not alter the chemical composition of the substance.

* These processes occur due to changes in temperature and pressure.

* Sublimation and deposition are relatively uncommon compared to melting/freezing and boiling/condensation, but they play significant roles in various natural processes.

Let me know if you have any other questions.