Matter In Our Surroundings l Part 5 l Evaporation l

Опубликовано: 02 Апрель 2025
на канале: CBSE বাংলা

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Matter In Our Surroundings l Part 5 l Evaporation l #chemistry #cbseবাংলা #science Matter In Our Surroundings l Part 5 l Evaporation l #chemistry #cbseবাংলা #science

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In this video I will explain the Evaporation, Cause Evaporation, Factors of Evaporation and Cooling effect of Evaporation.

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Class 9 Chemistry Chapter 1
Part 1:    • Matter in our surroundings l Part 1 l...
Part 2:    • Matter In Our Surroundings l Part 2 l...
Part 3:    • Matter In Our Surroundings l Part 3 l...
Part 4:    • Matter In Our Surroundings l Part 4 l...

Latest Updated Syllabus of Class 9 Science link:    • CBSE Class 9 Science Syllabus 2023-24...

Evaporation: Do we always need to heat or change pressure for changing the state of matter? Can you quote some examples from everyday life where change of state from liquid to vapour takes place without the liquid reaching the boiling point? Water, when left uncovered, slowly changes into vapour. Wet clothes dry up. What happens to water in the above two examples?? We know that particles of matter are always moving and are never at rest. At a given temperature in any gas, liquid or solid. there are particles with different amounts of kinetic energy. In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away. from the forces of attraction of other particles and gets converted into vapour. This phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation. You must have observed that the rate of evaporation increases with- an increase of surface area: We know that evaporation is a surface phenomenon. If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out. an increase of temperature: With the increase of temperature, more number of particles get enough kinetic energy to go into the vapour state. a decrease in humidity: Humidity is the amount of water vapour present in air. The air around us cannot hold more than a definite amount of water vapour at a given temperature. If the amount of water in air is already high, the rate of evaporation decreases. an increase in wind speed: It is a common observation that clothes dry faster on a windy day. With the Increase in wind speed, the particles of water vapour move away with the wind, decreasing the amount of water vapour in the surrounding.

FACTORS AFFECTING EVAPORATION

Let us understand this with an activity. How DOES EVAPORATION CAUSE COOLING? In an open vessel, the liquid keeps on evaporating. The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation. This absorption of energy from the surroundings make the surroundings cold. MATTER IN OUR SURROUNDINGS 8 What happens when you pour some acetone (nail polish remover) on your palm? The particles gain energy from your palm or water? surroundings and evaporate causing the palm to feel cool. Why do we see water droplets on the outer surface of a glass containing ice-cold Let us take some ice-cold water in a tumbler. Soon we will see water droplets on After a hot sunny day, people sprinkle the outer surface of the tumbler. The water vapour present in air, on coming in contact with the cold glass of water, loses energy and gets converted to liquid state, which we see as water droplets. water on the roof or open ground because the large latent heat of vaporisation of water helps to cool the hot surface. Can you ette some more examples from daily life where we can feel the effect of cooling due to evaporation? Why should we wear cotton clothes in summer? uestions 1. Why does a desert cooler cool better on a hot dry day? During summer, we perspire more because of the mechanism of our body which keeps us cool. We know that during evaporation, the particles at the surface of the liquid gain energy from the surroundings or body surface and change into vapour. The heat energy equal to the latent heat of vaporisation is absorbed from the body. leaving the body cool. Cotton, being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation. ER 2. How does the water kept in an earthen pot (matkal become cool during summer? 3. Why does our palm feel cold when we put sorne acetone petrol or perfume on it? Why are we able to stp hot milk faster from a saucer than a cup? 5. What type of clothes shoul wear in summer?

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