Why evaporation causes coldness; a challenge to the
second law of thermodynamics | ||||||||
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In surface
evaporation the liquid increases the potential energy of its
molecules by taking heat while their kinetic energies remain
unchanged. In such state the molecules are in the form of a gas
(vapor). We know that in an isothermal system of a liquid and a
gas adjacent to it, the temperature of the gas decreases due to
the surface evaporation while some net heat is transferred from
the gas to the liquid. So, if the temperature of the gas is lower
than the temperature of the liquid only in a sufficiently small
extent, some net heat will be still transferred from the gas to
the liquid due to the surface evaporation and finally the gas and
liquid (and vapor) will be isothermal (in a temperature lower than
the initial temperature). This matter violates the Clausius (or
refrigerator) statement of the second law of thermodynamics.
KEYWORDS: evaporation, surface, thermodynamics, second, law
PACS: 64.70.fm , 68.03.Fg , 05.70.Np , 05.70.Fh , 05.90.+m , 68.35.Md
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