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Basics Of Evaporation

Basics Of Evaporation. By Moizul Hasan Assistant Professor. Warm-up. Wet floor is left to dry up. Feeling cool under air-conditioner. Ironing wet clothes to dry them. Are these examples of evaporation?. . Warm-up. Put it inside a room with all windows closed.

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Basics Of Evaporation

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  1. Basics Of Evaporation By Moizul Hasan Assistant Professor

  2. Warm-up Wet floor is left to dry up. Feeling cool under air-conditioner. Ironing wet clothes to dry them. Are these examples of evaporation? 

  3. Warm-up Put it inside a room with allwindows closed. It is muggyand is going torain. Strong sunlight shines on it. The plant is under a sea breeze. Do you think the leaves of a plant getdry quickly in these cases?  

  4. Warm-up A bit warmer than it would be. A bit cooler than it would be. No change. Others: _________ How does the formation of snow or rain affect the temperature of the air? 

  5. Introduction • Liquid can change to vapour at temperatures below the boiling point. • A liquid changing into a vapour is said to be evaporating. The process is called evaporation.

  6. Differences between evaporation and boiling • Evaporation and boiling require latent heat of vaporization.

  7. 1 Cooling effect of evaporation Apply perfume/alcohol to your body... What do you feel? COOL ! Perfume/alcohol evaporates easily and takes the energy from your body.

  8. 1 Cooling effect of evaporation Sweat comes out of the pores, evaporates thus taking energy away from the skin. So we feel cool!

  9. 1 Cooling effect of evaporation On a humidday, the air is full of water vapour. This slows down the evaporation of sweat. Sweat tends to stay on the skin. No cooling effect occurs. So, we feel hot.

  10. 1 Cooling effect of evaporation You can easily catch a cold if you are wet. As you dry out, latent heat is taken from your body. If it is windy, you cool down even more.

  11. Different particles have different velocity. 2 Evaporation and particle motion Evaporation is the escape of fast-moving particles from the surface of a liquid. Thus, some have higher K.E.!

  12. fast molecules (high KE) near the surface may escape E 2 Evaporation and particle motion slow molecules left behind  average KE of the remaining molecules decreases  temperature of liquid   cooling effect

  13. 3 Factors affecting evaporation Points to consider: 1 Fast-moving particles in liquid escape and become vapour;

  14. 3 Factors affecting evaporation 2 While slow-movingparticles in vapour stick back to the liquid. 3 The rate of evaporation (dryingup) is a balance between the rate of escape and the rate of return.

  15. More molecules can escape. Temperature of water The rate of evaporation increases with thetemperature of the liquid Molecules have more KE Molecules move faster on average.

  16. Surface area of water When surface area is increased… larger the surface area, more molecules can escape at the same time. Greater is the rateof evaporation.

  17. evaporation Humidity of air • If the air is humid, it is full of water vapour. • Waterparticles in vapour have greater chance to return to the liquid. • more humid the air, Some return the lower the rate of evaporation.

  18. Movement of air If there is a breeze, the particles that escape from thesurface of water get blown away. fewer particles in the vapourreturn to the liquid. a breeze increases the rate of evaporation.

  19. Condensation  the opposite of evaporation • Warm air can hold more water. • If warm humid air suddenly cools, some of the vapour has to condense.

  20. Condensation  the opposite of evaporation • This is how clouds andmist are formed frommillions of tiny waterdroplets. • Latent heat of vaporizationis released when watervapour condenses.

  21. Soup covered with oil… longer Soup covered with oil takes ________ (longer/shorter) to cool down... …because the oil layer __________(slows/enhances) the evaporation of water (soup) slows

  22. True or false: When... True or false: When water vapour condenses, the surrounding air is warmed. (T/F)

  23. Name the factors that increase the rate of evaporation. Increasing water temperature, ____________________________________________________________________________________________________________________________________________ Decreasing humidity, Increasing surface area of water, Increasing air movement

  24. Example 7 (a) State a precaution in this experiment. Switch on the heater only when it is immersed in water; otherwise it may bedamaged.

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