What is evaporation?

What is evaporation? What causes evaporation to occur? What are some real life examples of evaporation? These questions will be answered here.

Water can have 3 states - solid, liquid, and gas. 

Evaporation is the process by which water goes from the liquid state to gas or water vapor.

Since gas is less dense or lighter than air, it will rise in the atmosphere to eventually form clouds. 

For example, if you put water in an open container and forget about it, the water will eventually dry up or evaporate completely.

The water from rivers, ponds, lakes, and the ocean all evaporate and rise in the atmosphere.

What causes evaporation?

Evaporation is obvious when boiling water. Once the temperature of the water reaches 212 degrees Fahrenheit, you can clearly see water vapor rising from the pot.

However, the water in lakes, ponds, rivers, and the ocean does not usually reach 212 degrees Fahrenheit. Moreover, as we mentioned before, even if you don't boil the water, it will evaporate eventually anyway.

Therefore, there has to be some other kind of mechanism that causes the water to evaporate other than temperature.

The mechanism behind evaporation is kinetic energy!

Recall that kinetic energy refers to energy of motion or the capability of an object to do work while moving.

Molecules in water have kinetic energy. This means that these molecules can move in all directions.

As they move, they can bump into one another. When they bump into one another, some of the molecules lose kinetic energy while others gain kinetic energy.

Something interesting happen when the molecules at the surface of the water get bumped!

The molecules at the surface may already have their own kinetic energy.

When these molecules at the surface of the water get bumped from the molecules beneath, they gain even more kinetic energy.

As a result they break free from the water and fly into space as water vapor. 

The molecules on the surface gained kinetic energy before flying in the air. However, the molecules that bumped the ones that flew out of the water lost their kinetic energy instead. Evaporation is a cooling process!

Why is evaporation a cooling process?

In the lesson about temperature, we saw that temperature and kinetic energy are related. We saw that the warmer something is, the higher the kinetic energy. 

Since the molecules in the water lost their kinetic energy while bumping the ones at the surface, the water got a little colder.

This explains why after drinking a cup of hot tea or playing a sport, your body cools down. Yeah! That is right! Drinking hot liquids or playing a sport will actually cool you down.

When you drink hot tea or play basketball for instance, your body will overheat. This will in turn trigger your sweat glands and you will sweat.

As the sweat evaporates, the sweat that remains on your body cools down. This in turn cools down your body by conduction.

That is why you feel so cold after you are done with your hot tea, or done playing basketball or some other sport.