Dry ice

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Dry ice, sometimes referred to as "Cardice" or as "card ice" is the solid form of carbon dioxide.

Dry ice is used as a cooling agent. Moreover, for some applications, the convenience of its sublimation "into thin air," in contrast to the melt-water left by warming water ice, may outweigh other costs.

Contents

Properties

Dry ice is the solid form of carbon dioxide (chemical formula: CO2), comprising two oxygen atoms bonded to a single carbon atom. It is colourless, odourless, non-flammable, and slightly acidic.[1]

At temperatures above −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).[2] 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.[3] 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.[4] The composition results in low thermal and electrical conductivity.[5]

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