When left unattended, dry ice (solid carbon dioxide) undergoes sublimation, which is a physical change. During this process, the solid dry ice directly transforms into a gas (carbon dioxide), without passing through the liquid phase. The gaseous carbon dioxide disperses into the surrounding air.

The chemical composition and molecular structure of dry ice remain the same during sublimation. Therefore, it is considered a physical change rather than a chemical change. In physical changes, the substance's chemical composition and identity do not change, only the physical form or state (solid, liquid, or gas) changes.