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Evaporation

  • Last Updated : 14 Jul, 2021

Have you dried up your wet clothes in hot summers? Do you know where the water goes from the cloth? Well, due to the sun, water gets converted into water vapour, and it is called evaporation. So, evaporation refers to the process in which the liquid state of matter changes into the gaseous state (vapour). Also, evaporation requires heat.

What is Evaporation?

Evaporation is a process where the liquid state of matter converted into a gaseous state of matter in the presence of heat. Many people got confused between evaporation and boiling as in boiling also liquid changes to a gaseous state. But, there is a difference, the very first is boiling of liquid happen at a particular temperature while evaporation can happen at any temperature below the boiling point. Also boiling is a bulk phenomenon whereas evaporation is a surface phenomenon, which means evaporation can happen only at the surface of the liquid. During evaporation, the molecule having higher kinetic energy only dissipated from the topmost layer of the liquid. There is also one unique property of evaporation that evaporation causes a cooling effect. The earthen pot used to store cool water in summers as the water got ooze out from tiny pores of the pot causing evaporation and leads to cool down the water inside the pot. Desert cooler also works on the principle of evaporation.

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Evaporation depends on some factors too, like temperature, the surface area of the liquid, wind speed and humidity. We will discuss this in detail in this article.



Examples of Evaporation

There are many examples of evaporation but here we are discussing only a few of them:

  1. Drying of clothes in sun: We all dried up our clothes in the sun, the wet clothes get dries up because of evaporation where the water turns into water vapour.
  2. Drying of water bodies: We have seen in summer water in the ponds and lake get decrease or sometimes dried up due to evaporation.
  3. Water cycle: This is a very good example of evaporation, in the above two we discussed how evaporation turns water into water vapour. This water vapour further goes to the sky and get condensed to form a cloud, and later it got precipitated. So, evaporation is very important to regulate the water cycle.
  4. Salt formation: Naturally or industrially salt form due to evaporation where the water gets evaporated to leave us salt.
  5. Drying of a Mopped Floor
  6. Working of the desert cooler in summers.

Factor affecting Evaporation

So far we discussed what is evaporation and how it is useful for us. Evaporation eases our life in many ways, and even it is contributing to the water cycle too. But evaporation is dependent on some factors which will be going to control the rate of evaporation. One more thing to note evaporation is a slow process but some external factors and increase or slow down the rate of evaporation. Let’s discuss all these factors of evaporation:

Temperature

The very first factor is temperature since we know evaporation can happen at any temperature before the boiling point, but the temperature has a role in evaporation too. It will determine the rate of evaporation, the more the temperature more is the rate of evaporation. Now the question is how? We all know the temperature will increase the kinetic energy, as the energy used to break intermolecular forces that bind the liquid molecule. So, when we apply more temperature the molecule fastly break their intermolecular forces and get evaporated. 

 So we can write:

Temperature ∝ Evaporation

Example: We all have seen in the hot summer clothes get fastly dried up than normal days. This is due to the Temperature factor.

Surface Area of the Liquid

Earlier we have discussed that evaporation is a surface phenomenon, and surface plays a role in the rate of evaporation. More is a surface area more will be the rate of evaporation. So, if more surface area will be there then the more liquid molecule will present on the surface, meaning more molecules break their inter-molecular bonds which will increase the rate of evaporation. So we can write it as;



Surface area of liquid ∝ Evaporation

Example: The same amount of water get evaporated quickly in a plate than the water in a shallow cup, this is because the plate offers a greater surface area for the liquid than the shallow cup.

Humidity

Humidity refers to the amount of wetness or water vapour in the air. The more water vapour in the air we will say more is humidity. With more humidity the rate of evaporation gets decrease.

Humidity ∝ 1/Evaporation

Example: In the rainy season when our surrounding is more humid than it is very difficult to dry up our clothes.

Wind Speed

Wind speed is directly proportional to evaporation means with the increase of wind speed there would be an increase in the rate of evaporation.

Wind Speed ∝ Evaporation

Example: On a windy day clothes get quickly dried up than the normal days. This is because the wind decreased the humidity which will increase the rate of evaporation.

Sample Questions

Question 1: Define evaporation with an example.

Answer:



Evaporation is a process where the liquid state of matter converted into a gaseous state of matter in the presence of heat. 

For example, We all dried up our clothes in the sun, the wet clothes get dries up because of evaporation where the water turns into water vapour.

Question 2: Why it is very difficult to dry up the clothes in the humid season?

Answer:

Since we know that humidity refers to the amount of wetness or water vapour in the air. The more water vapour in the air we will say more is humidity. With more humidity the rate of evaporation gets decrease Thus, it will become very hard to dry up the clothes in the humid season.

Question 3: Write four examples of evaporation.

Answer:

Examples of evaporation are as follows:

1. Drying of water bodies: We have seen in summer water in the ponds and lake get decrease or sometimes dried up due to evaporation.

2. Water cycle: This is a very good example of evaporation, in the above two we discussed how evaporation turns water into water vapour this water vapour further go to the sky and get condensed to form a cloud, and later it got precipitated. So, evaporation is very important to regulate the water cycle.



3. Salt formation: Naturally or industrially salt form due to evaporation where the water gets evaporated to leave us salt.

4. Drying of a Mopped Floor

Question 4: How increase in temperature affects the rate of evaporation?

Answer: 

Since we know evaporation can happen at any temperature before the boiling point, but the temperature has a role in evaporation too. It will determine the rate of evaporation, the more the temperature more is the rate of evaporation. Now the question is how? We all know that the temperature will increase the kinetic energy, and the energy used to break intermolecular forces that bind the liquid molecule. So, when we apply more temperature the molecule fastly break their intermolecular forces and fastly get evaporated. 

Question 5: Write any 3 factors which affect evaporation.

Answer:

Following are some factors that determine the rate of evaporation:

1. Surface area of the liquid: More is a surface area more will be the rate of evaporation. Thus, the Surface area of liquid ∝ Evaporation. For example, the same amount of water gets evaporated quickly in a plate than the water in a shallow cup, this is because the plate offers a greater surface area for the liquid than the shallow cup.

2. Humidity: With more humidity, the rate of evaporation gets decrease, means Humidity ∝ 1/Evaporation. For example in the rainy season when our surrounding is more humid than it is very difficult to dry up our clothes.

3. Wind Speed: Wind speed is directly proportional to evaporation means with the increase of wind speed there would be an increase in the rate of evaporation, which means Wind Speed ∝ Evaporation. For example, on a windy day, clothes get quickly dried up than the normal days. This is because the wind decreased the humidity which will increase the rate of evaporation.




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