Cooling by evaporation explained by the kinetic theory

Cooling by evaporation explained by the kinetic theory

The molecules of a liquid have an average kinetic energy which increases with temperature. Molecules near the surface which happen to be moving faster than average can escape from the attraction of their neighbours and escape out of the liquid. Some
of these may collide with other molecules above the liquid and so bounce back into it. But many others may escape altogether and their escape will be assisted if a current of air is passed over or through the liquid. Bubbling air through a liquid also increases the rate of evaporation by increasing the surface area from which molecules may escape.

In this way the liquid loses its most energetic molecules while the less energetic ones are left behind. The average kinetic energy of the remaining molecules is therefore reduced and this results in a fall in temperature.

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