Physics - evaporation

Question 1

What happens to the water in evaporation/where does it go?

Answer 1

The liquid water changes into a gas and becomes a part of the air. This gas is called water vapour

Question 2

Define evaporation

Answer 2

Evaporation is the change of state from liquid to gas at any temperature. Whenever a liquid changes into a gas, we say that it evaporates.

Question 3

What are volatile liquids?

Answer 3

Volatile liquids are liquids which evaporate very quickly.

Question 4

What are the features of evaporation (differences between evaporation and boiling)

Answer 4

1. Evaporation is a slow process
2. It takes place at any temperature
3. Evaporation takes place at only the surface of the liquid
4. In evaporation, heat is taken from the surroundings
5. Bubbles cannot be seen

Question 5

What are the features of boiling?

Answer 5

1. Boiling is a quick process
2. It takes place at a particular temperature
3. Boiling takes place throughout/within the whole liquid
4. In boiling, heat is supplied from an energy source
5. Bubbles can be seen

Question 6

How do liquids evaporate?/How does evaporation cause cooling?
(small diagram with this explanation)

Answer 6

1. In a liquid, the molecules vibrate and move around freely, but are close enough to attract each other.
2. As the liquid warms up, the speed of the molecules increase.
3. However not all molecules move at the same speed. some move faster, some move slower.
4. Sometimes a molecule gains enough energy to break free of the surface and escape into the environment.
5. It is the faster and hotter molecules who escape, leaving behind the slower and colder ones.
6. As the high - energetic molecules have escaped, the speed of the remaining molecules is slower. Consequently, the liquid has a slightly lower temperature and is cooler. Thus, we can say that evaporation has a cooling effect/can cause cooling,

Question 7

What is latent heat?

Answer 7

The hidden heat needed to make a solid melt/liquid boil

Question 8

How does sweat cool our body

Answer 8

Evaporation has a cooling effect. It requires latent heat. The sweat takes in latent heat from our body to use the heat energy to evaporate. As the heat is being used up, our body loses heat and we feel cool.
This is because it is the faster and hotter molecules that escape, leaving behind the slower and colder ones.

Question 9

What are the factors affecting the rate of evaporation

Answer 9

1. Temperature
2. Humidity of Surrounding Air
3. Wind/moving air
4. Exposed Surface Area

Question 10

Explain how temperature affects the rate of evaporation

Answer 10

The rate of evaporation increases with temperature. A warmer liquid (with a higher temperature) means that a greater number of molecules on the surface are more energized to escape

Question 11

Explain how the humidity in the surrounding air affects evaporation

Answer 11

Very damp air is called “humid”. Therefore, humidity is the measure of the amount of water vapour present in the air