Question

which condition out of the following will increase the evaporation of water?

(a) Increase in temperature of water
(b) Decrease in temperature of water
(c) Less exposed surface area of water
(d) Adding common salt to water

NCERT Class IX
Sciences - Exemplar Problems

Answer 1

$\mathbb{ ANSWER }$ :

The correct option is $\bf{ (a) }$

Increase in temperature of water will increase the exception of water. It is because, on increasing the temperature, kinetic energy of water molecules increases and more particles get enough kinetic energy to go into the vapour state.

This increase the rate of evaporation. Evaporation is the surface phenomenon so it depends upon the exposed surface area. Higher the exposed surface area of water, higher will be the evaporation. When common salt is added to water then the surface is occupied by the solvent as well as non-volatile solute particles.

So, the escaping tendency of solvent particles decreases and thus the evaporation of water decreases.

Therefore, other options (b), (c) and (d) will decrease the evaporation of water.

Answer 2

Answer:

Increase in temperature of water increases the evaporation of water.

Therefore, the option (a) is correct.

Explanation:

• On increasing the temperature, kinetic energy of water molecules will increase. More number of molecules of water get enough kinetic energy to escape from the liquid state.
• Therefore, more number of molecules will go into vapor state which increase the rate of evaporation.
• Evaporation is a kind of surface phenomenon because it depends upon the exposed surface area. Higher the area of surface will be exposed of water, higher will be the evaporation of water.
• On the addition of common salt into water. The surface will be occupied by the solvent (water) as well as non-volatile solute particles (salt). So, the escaping tendency of water molecules will be decreased and thus the rate of evaporation of water will decrease.