[Chemistry Class Notes] Evaporation Causes Cooling Pdf for Exam

In the previous classes, you have studied about three natural phenomena, evaporation, condensation, and vaporization. In this concept page, we will dig a little deeper to find out the underlying physical reasons behind these phenomena. This part of the chapter will concentrate on the evaporation and condensation part. The concept page has been developed by the top experts of so that every student can easily grab hold of the basic Physics behind these phenomena and answer the questions perfectly. 

This is an important part of chapter ‘matter’. These concepts will become a mandatory part of the physical properties of different elements and compounds in the advanced chapters. Here, evaporation and condensation will be properly discussed so that the students can understand their meaning and find the basic differences between them. Follow this concept page as a reference and study the chapter properly to overcome your doubts and answer the questions easily.

What is Evaporation?

Evaporation is a natural phenomenon where the molecules of a liquid convert into vapour and are released free from the surface. It can happen at any temperature. The prime reason for creating a concept page where you will define evaporation is to simplify the difference between evaporation and vaporization. These two terms might sound similar to each other but vary based on physical concepts.

Evaporation is a surface phenomenon where any liquid can release its molecules into the air by using the surrounding heat or the heat from the liquid itself. The rate of evaporation depends on the temperature of the liquid. The higher the temperature the quicker is the rate of evaporation. Even if the temperature of the liquid reaches the same level as that of the surrounding, it will still release molecules into the air.

Let us consider a few examples to make this concept clearer.  When we spread water on our skin, we feel cooler than normal. It is because the water molecules absorb the heat of our body and convert into gas molecules. The heat lost from our skin makes us feel cooler. The same happens when any volatile liquid is spread on our skin such as alcohols, acetone, etc. If a liquid evaporates faster, it will take up the heat from our skin at a faster rate making us feel colder than the other liquids.

Factors Affecting Evaporation Rate

There are quite a lot of factors that affect the rate of evaporation of a substance. Let us discuss some of the various factors that are affecting the evaporation of a substance. These are as – 

1. Temperature: The rate of the evaporation of a substance is directly proportional to the temperature of the atmosphere around the substance. The temperature increases the rate of evaporation due to the increased temperature will increase the kinetic energy of the liquid.

2. Humidity of the atmosphere or the air: if there is already a high amount of vapours present in the atmosphere then it will become difficult for a liquid particle on the surface to rise and come to an already saturated atmosphere. Hence, the humidity of the air is inversely proportional to the evaporation rate.

3. Surface Area: the surface area of which the given liquid is exposed to the air, also plays its role in determining the evaporation rate as the evaporation can only happen on the surface area exposed to the air. Hence, the more the exposed area, the more evaporation will occur.

4. Intermolecular Force of attraction: Intermolecular force will also decide the rate of evaporation or even if the evaporation will happen at a given set of conditions. These forces will vary for each liquid and the impurities present in it.

5, Wind Speed: If the speed of the wind increases, then the rate of evaporation will also increase. It is also one of the reasons why the clothes will dry easily on a windy day.

How Does Evaporation Cause Cooling?

Now that you have understood the definition and meaning of evaporation, you can easily find out why evaporation causes cooling. Let us consider another example. Earthen pots are capable of cooling water lower than room temperature. The prime reason behind such a cooling effect is that the earthen pots have minute pores from where water seeps out. This seeping water absorbs the heat from the water inside the pot and evaporates. Thus, it reduces the temperature of the water inside the pot making it cooler and more soothing to drink during the summer season.

You will also notice that the rate of cooling slows down in the rainy season and heightens in the summer season. As mentioned earlier, the rate of evaporation depends on the temperature, it also depends on the relative humidity of the atmosphere. The lower the humidity, the higher the rate of evaporation, the cooler becomes the water inside the earthen pot.

Applications of Evaporation

Continue reading the concept page formatted to make evaporation easier to understand. You will find exceptional use of evaporation too. Here is a list of applications of evaporative cooling you will find relevant to our daily lives.

• Perspiration is the natural way of cooling our body and maintaining the core temperature. Our sweat glands produce sweat. This sweat then takes up the heat from our skin to reduce our body temperature.

• Cotton clothes are worn in the summer season. These clothes absorb water from sweat and then act as a coolant using the same working principle.

• You have already read about the earthen pots. It is an exceptional example of how evaporation was used to cool water by our ancestors.

Use the evaporation meaning and find out the reason behind such natural phenomena.

What is Condensation?

Condensation, on the other hand, is the exact opposite of evaporation. Water vapour comes in contact with a cooler surface and releases the heat stored in it. Due to the loss of heat, water vapour condenses to form small liquid droplets on the same surface. This phenomenon is called condensation. You have now understood what condensation means. You can easily set a few examples on your own.