What process occurs when dry ice disappears?

When dry ice, which is solid carbon dioxide, disappears, it undergoes sublimation. Sublimation is the process in which a solid transitions directly into a gas without passing through the liquid state. This phenomenon occurs because dry ice is kept at extremely low temperatures, and when exposed to normal atmospheric conditions, it absorbs energy (heat) and the solid carbon dioxide molecules gain enough kinetic energy to break free of the solid structure, converting directly to gas.

This process is characterized by the rapid transformation you observe when dry ice is left out in open air, as it seemingly 'disappears' while producing a dense fog, which is actually cold carbon dioxide gas condensing moisture in the air. Understanding sublimation is essential in refrigeration and HVAC systems, particularly for substances like dry ice that serve as effective cooling agents due to their ability to cool surroundings rapidly without needing to be in a liquid form.