Sublimation: definition in chemistry
Sublimation: The change of a solid directly into a gas, without first becoming a liquid.
Sublimation absorbs heat, because particles must gain enough energy to escape from the solid straight into the gas. Dry ice sublimes because liquid carbon dioxide cannot exist at ordinary atmospheric pressure, while solids such as iodine sublime readily when warmed even though they can also melt. The reverse change, from gas directly to solid, is called deposition, and it is how frost forms on cold nights.
Examples
- Dry ice (solid CO₂) turning into gas at −78.5 °C
- Iodine crystals giving off violet vapor when gently heated
- Snow slowly disappearing on cold, dry, windy days without melting
- Freeze-dried coffee made by subliming ice under low pressure
On the periodic table
Iodine in group 17 and arsenic in group 15 sublime readily, and arsenic sublimes rather than melts at normal atmospheric pressure.