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

2. Warm-up Do you think the leaves of a plant get dry quickly in these cases?   Put it inside a room with all windows closed. It is muggy and is going to rain. Strong sunlight shines on it. The plant is under a sea breeze.

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

7. 1 Cooling effect of evaporation Sweat comes out of the pores, evaporates thus taking energy away from the skin. So we feel cool!

8. 1 Cooling effect of evaporation No cooling effect occurs. So, we feel hot. On a humid day, the air is full of water vapour . This slows down the evaporation of sweat. S weat tends to stay on the skin.

10. 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.! Different particles have different velocity.

11. Simulation

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

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

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

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

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

21. A E = ml v applies to boiling but not to evaporation. B Boiling always occurs at a definite temperature but evaporation does not. C Boiling takes place at the surface, but evaporation occurs within the liquid. D Bubbles are formed violently in boiling, but slowly in evaporation. Which is the difference between boiling and evaporation?

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

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

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

25. Example 6 A person (mass 60 kg) doing exercise is covered with sweat . (a) If 1 litre (1 kg) of sweat is evaporated in 1 hour... … how much energy is required to evaporate this amount of water?

28. Example 6 Apply E = mc  T ,  T = E / mc = 2.26  10 6 / (60  3500) If the energy were not removed from the body by sweating,... ... the body temperature would increase by 10.8 °C.  T = 10.8 °C

29. Example 7 The experimental set-up is used to find the specific latent heat of vaporization of water . the electronic balance measures the mass of water boiled away

33. Example 7 Some water in the polystyrene cup evaporates ... … and thus the balance reading drops. (d) After the heater has been switched off for a period of time, the reading shown on the balance drops slightly. Why?