Evaporation:
Evaporation is a process in which liquid turns into vapour or gas below its boiling point.
Only molecules with high energy can overcome the forces of attraction and evaporate.
Only the molecules at the surface of the liquid evaporate
Cooling Effect of Evaporation:
When evaporation occurs, the molecules of water with greater Kinetic energy escape from its surface. So the molecules of water with lower Kinetic energy are left behind. This results in a decrease in the temperature of water. Hence, evaporation causes cooling.
e.g. When we step out of a shower the water on our body evaporates using the heat energy from out skin. This causes us to feel cold.
Boiling v Evaporation:
Although in both boiling and evaporation the liquid turns into vapor, they are two different phenomena. The table below lists their differences.
Factors affecting the Rate of Evaporation
Temperature: With the increase in temperature the rate of evaporation also increases.
Wind Speed: Rate of evaporation also increases with the increase in wind speed.
Surface area of liquid: Rate of evaporation increases with the increase in surface area of liquid.
Humidity: The rate of evaporation decreases with increase in humidity.
Nature of liquid: Nature of liquid also effect the rate of evaporation. Liquid with lower boiling points have grater vapor pressure and evaporate more rapidly.
Solute Concentration: Increased concentration reduces evaporation. Salty water evaporates more slowly than pure water
