Dry ice

Dry ice, sometimes referred to as "cardice" (chiefly by British chemists), is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). It is useful for preserving frozen foods where mechanical cooling is unavailable.

Dry ice sublimates at −78.5 °C (−109.3 °F) at Earth atmospheric pressures. This extreme cold makes the solid dangerous to handle without protection due to burns caused by freezing (frostbite). While generally not very toxic, the outgassing from it can cause hypercapnia (abnormally elevated carbon dioxide levels in the blood) due to buildup in confined locations.

Dry ice is the solid form of carbon dioxide (CO₂), a molecule consisting of a single carbon atom bonded to two oxygen atoms. Dry ice is colorless, non-flammable, with a sour zesty odor, and can lower the pH of a solution when dissolved in water, forming carbonic acid (H₂CO₃).

At pressures below 5.13 atm and temperatures below −56.4 °C (−69.5 °F) (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).

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