Sublimation
The direct conversion of a solid into a vapour without passing through the liquid state.
Formula / equation
ΔH_sub = ΔH_fus + ΔH_vap
Unit
kJ/mol
In depth
Sublimation occurs when the ambient pressure is below the substance's triple point pressure, so no liquid phase is stable. It is exploited to purify volatile solids, since non-volatile impurities are left behind, and in freeze-drying, where ice sublimes from frozen material under vacuum.
Examples in the real world
Solid CO₂ subliming at −78 °C; iodine giving violet vapour on gentle warming; naphthalene mothballs disappearing.