MadSci Network: Chemistry

Re: Does water evaporate at all temperatures?

Date: Thu May 12 09:51:02 2005
Posted By: Ara Kooser, Grad student, Physical Chemistry, Sandia National Labs
Area of science: Chemistry
ID: 1115760737.Ch

   Actually liquid or solid water evaporates at all temperatures. As long
as there is enough kinetic energy for a water molecule to escape the
intermolecular forces water evaporates. You can do a neat little
qualitative experiment by putting an ice cube in a no-frost freezer and
watch what happens (it sublimes). So to answer your question there is no
particular temperature that evaporation starts and stops.

   Absolute zero is usually defined as a cease in all atomic motion. This
is incorrect (or plain wrong if you want to use less polite language).
There still is translational motion in the atoms. A better definition is:
absolute zero is the temperature where no further energy may be extracted
from the system. As you approach absolute zero you still have
evaporation(1) but at absolute zero I don't know (nor have I found any
information, yet). You could do a thought experiment given the definition
of absolute zero and the requirements for evaporation. Then work out the
answer on paper.

(1) The evaporation rate, free energy, and entropy of amorphous water at
150 K  Speedy et. al.  The Journal of Chemical Physics -- July 1, 1996 --
Volume 105, Issue 1, pp. 240-244

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