The process of a substance changing from a solid to a gas is called sublimation.

Here's a breakdown:

* Solid: In a solid, particles are tightly packed and have a fixed shape and volume.

* Gas: In a gas, particles are far apart and move freely, taking the shape and volume of their container.

During sublimation, the solid absorbs enough energy (usually heat) to overcome the attractive forces holding its particles together. This causes the particles to break free from their fixed positions and move around as a gas.

Examples of sublimation:

* Dry ice (solid carbon dioxide) sublimes directly into gaseous carbon dioxide at room temperature.

* Mothballs slowly sublimate, releasing a vapor that repels moths.

* Frozen water (ice) can sublimate at temperatures below freezing, especially in dry conditions.

Let me know if you'd like to learn more about the process of sublimation!