Sublimation and Lantent Heat
Name: pat j bushong
It is like this : Sublimation happens all the time (eg: snow,
and frost) so what is the latent heat of sublimation? I know from the
books that this is supposed to be a triple point deal, but if that e
were so then snow and frost would be extremely special! it takes 80 c/g
to turn ice into water and 540 c/g to turn water into steam, how many
calories per gram does it take to turn water vapor into ice???? (as in
frost and snow) this is driving us all mad here in the earth science/physics department -
all from a students question!!! please HELP!!! thanks...
You release energy in going from vapor to solid, right?
So somewhere around 600 calories per gram is released, and it
should be a very favorable reaction (especially at low temperatures
of course!) The energy released is presumably quickly taken away
by the air or whatever else is keeping the forming frost at
that low temperature. I assume the actually energy difference
depends strongly on temperature (the energy of the vapor is
certainly more temperature dependent than the energy of the solid
Yours is really a chemistry question, but I will take a stab at it.
There is something called Hess's law that says that a net enthalpy change
does not depend upon the steps between the initial and final states. Enthalpy
is a "state variable". The heat of sublimation is essentially the enthalpy
change; it measures the amount of energy required to break up the ionic
bonding in an ice crystal, and free up the molecules to make a gas. This
energy should therefore be the same as the net energy required to go from
solid -> liquid -> gas; the sum of the heats of fusion and vaporization.
Sublimation occurs because you are below the triple point; the relevant
pressure is the partial pressure of the H2O in the atmosphere.
Thanks for the question. Let me know if I got the
Jack L. Uretsky
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Update: June 2012