Classical Physics


Why Evaporation Causes Coldness; a Challenge to the Second Law of Thermodynamics

Authors: Hamid V. Ansari

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.

Comments: 11 pages

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[v1] 10 Aug 2009

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