Sublimation |
Evaporation from the solid state is called sublimation. Many substances, solid CO2 (dry ice), carbon, purple crystals of iodine, and water-ice or snow below zero degrees Celsius, evaporate directly to the gaseous state without first becoming liquids. When CO2 sublimes in warm water, frozen water vapor gives clouds of fog - which makes a good stage effect. When frozen wet clothes are hung outside in dry cold air they become dry over time. When food is left uncovered in a freezer it dries out. Both effects are due to sublimation. |
The specific latent heat of sublimation of water ice is the sum of the latent heats of fusion and evaporation (2840 kJ/kg at -30°C) The latent heat of sublimation of carbon is 716.7 kJ/mol or, since the mole is 12 grams of carbon, very nearly 60 MJ per kilogram at a temperature of 5100 K. The evaporation of carbon is a very energy intensive process. |