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Re: Vapor Pressure and Evaporation Rates



Not from the vapor pressure alone.  The (equilibrium) vapor pressure of a
liquid is essentially the amount of vapor that will be in equilibrium with a
liquid in a closed container (that has some space in it) at a particular
temperature.  It can be thought of as a tendency for the molecules to escape
from liquid as gas.  Clearly it is a function of temperature and pressure
(or volume: pV=nRT -- and for you purists out there, I should really put the
van der Waals equation and not the ideal gas law, because we are not dealing
with an ideal gas, but it's a similar idea).  Vapor pressure is an intrinsic
property of a substance.  Evaporation rate, on the other hand, is an
extensive property and depends not only on temperature and pressure but on
the surface area of the liquid evaporating.  I suggest you consult a
physical chemistry text, but evaporation rate is usually an empirical
measurement because it depends on several variables and is easier to measure
than to calculate.

Ruth Weiner
ruth_weiner@msn.com
-----Original Message-----
From: William Lorenzen <LORENZEN_W@A1.TCH.Harvard.edu>
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Date: Tuesday, August 01, 2000 4:41 PM
Subject: Vapor Pressure and Evaporation Rates


>          Is it possible to determine the evaporation rate of an organic
>          compound from it's vapor pressure?
>
>          Regards,
>
>          William A. Lorenzen
>          Children's Hospital
>          Boston, Ma 02115
>          lorenzen_w@a1.tch.harvard.edu
>
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