Illustrated Glossary of Organic Chemistry

Sublimation: The process in which a solid transforms into a gas phase without first melting to form a liquid phase. (Sublimation is not synonymous with evaporation; evaporation is a liquid-to-gas phase change.) Frequently happens with substances having a high vapor pressure at room temperature. Familiar substances that sublime readily include iodine (shown below), dry ice (shown below), menthol, and camphor. Sublimation is occasionally used in the laboratory as a method for purification of solids, for example, with caffeine.

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Solid iodine (the gray to black crystals) sublimes readily at room temperature, without melting first. The deep purple vapor condenses at the top of the jar, forming more crystals. Note the lack of liquid phase in this photo.

Dry ice is solid carbon dioxide at -78 oC. This substance converts to the gas phase by sublimation without first forming liquid carbon dioxide. Click on the image to see a time-lapse video of dry ice sublimation. Note the absence of any liquid accumulation. (The video shows frost, water ice, and a little bit of liquid water, but no liquid carbon dioxide.)