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Name: Kirsty L.
Status: student
Age: 16
Location: N/A
Country: N/A
Date: 2001 - 2002

when matter changes state the energy need is measured as specific latent heat, either fusion or vaporisation. but what happens when solid CO2 sublimes? effectively it goes though fusion and vaporisation in one, so will the energy needed for it to change state be twice as great as that of something that only has one state change to go through. what is the energy needed for CO2 to sublime called?

CO2 does not go through fusion and vaporization "in one". At 1 atm pressure it goes directly from the solid to the gas with no intermediate liquid phase. This temperature is 194.67 kelvin and the heat of sublimation (or more rigorously the enthalpy of sublimation) is 6030 +/- 5 cal/mol.

Vince Calder

What an interesting question. It is nice to see you thinking about this. One thing your high school textbook may not mention is something called the heat of sublimation, which is the "energy need" to go from solid to gas state. It's not going through two states--solid carbon dioxide goes directly to the gas state. This can also happen with solid water (ice) and some other compounds if the conditions are right. We are more familiar with the carbon dioxide example because we see it in haunted houses, movies, etc.

Pat Rowe

The energy of sublimation is called, conveniently enough, the energy of sublimation. It is the sum of the energy of fusion and of evaporation. Generally, a substance's energy of vaporization is greater than its energy of fusion; the solid and liquid, both being concensed states, are closer to each other in energy than to the gas.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois

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