Properties
For supplementary chemical data, see Carbon dioxide (data page).Dry ice is the solid form of carbon dioxide (chemical formula CO2), comprising two oxygen atoms bonded to a single carbon atom. It is colorless, with a sour zesty odor, non-flammable, and slightly acidic.
At temperatures below −56.4 °C (−69.5 °F) and pressures below 5.13 atm (the triple point), CO2 changes from a solid to a gas with no intervening liquid form, through a process called sublimation. The opposite process is called deposition, where CO2 changes from the gas to solid phase (dry ice). At atmospheric pressure, sublimation/deposition occurs at −78.5 °C (−109.3 °F).
The density of dry ice varies, but usually ranges between about 1.4 and 1.6 g/cm3 (87–100 lb/ft3). The low temperature and direct sublimation to a gas makes dry ice an effective coolant, since it is colder than water ice and leaves no residue as it changes state. Its enthalpy of sublimation is 571 kJ/kg (25.2 kJ/mol).
Dry ice is non-polar, with a dipole moment of zero, so attractive intermolecular van der Waals forces operate. The composition results in low thermal and electrical conductivity.
Read more about this topic: Dry Ice
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