Dry Ice and Heat of Sublimation
Name: Kirsty L.
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.
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.
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.
PG Research Foundation, Darien, Illinois
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Update: June 2012