Page 1 - 3. LESSON NOTES-EVAPORATION

SAI International School
Class-IX

Subject-Chemistry
Topic-Matter in our surroundings
Sub topic- Evaporation

LESSON NOTES
Evaporation: The phenomenon of change of a liquid into vapours at any
temperature below its boiling point is called evaporation.

The process of evaporation can be explained as follows: Some particles in liquid
always have more kinetic energy than the others. So, even when a liquid is well
below its boiling point, some of its particles have enough energy to break the forces
of attraction between the particles and escape from the surface of the liquid in the
form of vapour (or gas). Thus the fast moving particles (or molecules) of a liquid are
constantly escaping from the liquid to form vapour (or gas).

Difference between Evaporation and Boiling
1.Evaporation takes place at all temperatures, while boiling occurs at a particular
temperature.
2.Evaporation takes place from the surface, whereas the entire liquid boils.
3. Evaporation can occur using the internal energy of the system,
while boiling requires an external source of heat.

Factors affecting Evaporation:

The evaporation of a liquid depends mainly on the following factors:

1. Temperature
2. Surface area
3. Humidity
4. Wind speed

o We are well aware of the fact that evaporation is a surface phenomenon.
Therefore increasing the surface area increases the rate of evaporation.

o Increasing temperature also increases the rate of evaporation because with the
rise in temperature more number of particles get enough kinetic energy to
convert into vapour state.

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