Explain why evaporation causes cooling and give the factors which affect its rate. – NABTEB QUESTION

The molecules of the liquid have an average velocity or average kinetic energy which increases with temperature. Molecules near the surface which happen to move faster than the average, escape from the attraction of their neighours and out of the liquid. Thus the liquid loses its most energetic molecules while the less energetic ones are left behind. The average K.E. of the remaining molecules is therefore reduced, which lowers the temperature of the liquid hence evaporation causes cooling.

Factors affect evaporation are:

1. Temperature

2. Exposed area of liquid surface

3. Prevailing wind

4. Humidity

5. Prevailing atmospheric pressure