Wednesday, June 6, 2012

Why coffee cools when you blow on it?

When you blow on your cup of coffee evaporation takes place. In the evaporation the water molecules leaves the water surface and comes in the air. In this process the escaping water molecule has to overcome the force of attraction applied by the other water molecules of the surface. As we know that the force of attraction between the molecules is of electrostatic type. So escaping molecule must have enough kinetic energy to overcome the potential energy of this force of attraction. Since leaving molecules possess more energy than the ordinary ones. The left ones are of less energy than the average. Hence the random motion of molecules decreases. As you may know higher the random motion of molecules higher the temperature of the substance . So temperature of liquid decreases.

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