Question

A surface phenomenon.

Answer 1

Step-1:

Evaporation:

The process of changing the liquid state into a vapour state even below its boiling point is called Evaporation.

Step-2:

A surface phenomenon:

1. The process of evaporation is a surface phenomenon because it occurs on the surface.
2. which means that only those particles of the liquid change into vapours that are present on its surface. Some particles in a liquid always have more kinetic energy than others.
3. This energy is enough to break the forces of attraction between the particles and escape from the surface of the liquid in the form of water vapour. Thus, the fast-moving particles of a liquid constantly escape from the liquid to form vapours.

Step-3:

Process of Evaporation:

Since evaporation is a surface phenomenon when the surface area of the liquid is larger the rate of evaporation will be more.

Example:

1. when a liquid is kept in the test tube and the same liquid in the china dish. The liquid kept in the china dish will evaporate more rapidly because of its larger surface area as compared to the liquid in the test tube.
2. When we spread wet clothes to dry them in the air, there is an increase in surface area available for the evaporation of water to take place and hence the clothes get dried faster.

Step-4:

Experiment to show that surface area increases the rate of evaporation: