Question

It is desired to increase the rate of evaporation of a given quantity of a liquid. Suggest two ways, excluding the direct heating of the liquid, which can be used to bring about this increase in the rate of evaporation.

Answer 1

Increase the rate of airflow:

1. When a liquid is kept open for a long time, it reaches equilibrium with its gaseous form (vapour) above the surface.
2. In this situation, the rate of evaporation of the liquid is equal to the rate of condensation of the vapour.
3. When the concentration of the vapour above the surface is decreased the liquid is no longer in equilibrium with its gaseous form. As a result, the rate of evaporation increases.
4. As the rate of airflow increases the concentration of the vapour above the liquid decreases and the rate of evaporation increases.

Increase the surface area:

1. Evaporation of a liquid occurs from the surface.
2. Thus, the rate of evaporation of a liquid increase as the area exposed to air increases.
3. If we transfer the liquid to a vessel with a larger open surface than before the rate of evaporation will increase.