Matter in Our Surroundings- Blog 5

CHEMISTRY

Chapter 1: MATTER IN OUR SURROUNDINGS-V

HELLO BOYS!!

Let us continue our discussion of Evaporation

Today we will be looking at

1. The cooling Effect of Evaporation.

At the end of today's topic, learners will be able to:

1. Explain the cooling effect of evaporation.
2. Describe the cooling effect of Evaporation in their real life situation.

EVAPORATION CAUSES COOLING

The cooling caused by evaporation is based on the fact when the liquid evaporates, it draws the latent heat of vaporisation from anything which it touches. By loosing heat this anything gets cooled.

In an open vessel, the liquid keeps on evaporating. The particles of liquid absorb energy form the surrounding to regain the energy lost during evaporation. This absorption of energy from the surroundings make the surroundings cold.

1) If we put a little of spirit(nail polish remover or acetone) on our hand, the spirit evaporates rapidly and our hand feels very cool. This is due to the fact that to change liquid to vapour state, spirit requires latent heat of vaporisation. The spirit takes this heat of vaporisation from our hand. The hand loses heat and gets cooled.

2) During hot summer days,water is usually kept in an earthen pot to keep it cool. The earthen pot has a large number of extremely small pores in its walls. Some of the water continuously keeps seeping through these pores to the outside of the pot. This water evaporates continuously and takes the latent heat required for vaporization from the earthen pot and remaining water. In this way, the remaining water loses heat and gets cooled. 
(In-text Q2 Page no. 10)

3) At many places especially in villages people often sprinkle water on the ground in front of their homes during summer evening. This water evaporates by taking latent heat of vaporisation from the ground and surrounding air. By losing heat, the place become cool and comfortable.

4) Sweating is our body method of maintaining a constant temperature. On a hot day or after doing exercise, when our body temperature tends to rise too much, our sweat glands give out moisture on our skin. When this sweat evaporates, it takes latent heat of vaporisation from our body leaving the body cooler. 
(HINT: In-text Q5 Page no. 10 Which fabric absorbs sweat better?)

5) We should wear cotton clothes in hot summer days to keep cool and comfortable. We get lot of sweat on our body in hot summer days. Now cotton is a good absorber of water, so it absorbs the sweat from our body and expose it to the air for evaporation. The evaporation of this sweat cools our body.

6) A desert cooler cools better on a hot and dry day because the higher temperature on a hot day increases the rate of evaporation of water, and dryness (low humidity) of air also increases the rate of evaporation of water. And due to increased rate of evaporation of water, a desert cooler cools better on a hot and dry day. (In-text Q1 Page no. 10)

7) We are able to sip hot tea faster from a saucer than from a cup. This is because saucer has large surface area. Due to the large surface area, the evaporation of hot tea from saucer is faster leaving the tea cooler than before. (In-text Q4 Page no. 10)

This will enable you to answer the In-text questions on page no. 10. For the questions I did not cover here please watch

https://www.youtube.com/watch?v=651G5u49_3g

LET US SUMMARIZE THE LESSON:  https://www.youtube.com/watch?v=RXqMSP2DDfU

THIS IS ALL FOR THIS LESSON.
WE WILL TRY THE EXERCISES TOMORROW. PLEASE BE THOROUGH WITH ALL THE BLOGS

TAKE CARE!!!