"Vaporization and Liquefaction" PPT Courseware on Changes in State of Matter 4

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"Vaporization and Liquefaction" PPT Courseware on Changes in State of Matter 4

Thinking: 1. How did the alcohol "disappear"? Where did it go?

The process of a substance changing from a liquid state to a gaseous state is called vaporization.

2. When alcohol is placed in hot water, it will vaporize immediately. This shows what?

Vaporization needs to absorb heat.

Problem: 1. Wet clothes will dry out if exposed to the sun. Where did the water on the clothes go?

2. After boiling a pot of water, continue to heat it. The water in the pot will gradually decrease until it is boiled dry. Where did the water in the pot go?

(1) Evaporation

What is evaporation?

1. The vaporization phenomenon that occurs only on the surface of a liquid is called evaporation.

2. Evaporation can be carried out at any temperature.

3. Evaporation is relatively slow.

Characteristics of evaporation

1. Use a cotton swab dipped in alcohol and rub it on your hands. What will happen to the alcohol? How does your hand feel?

The alcohol has vaporized and the area where the alcohol was applied on your hands feels cold.

2. When the thermometer bubble is dipped in alcohol, what happens to the alcohol? How does the thermometer reading change?

The alcohol on the glass bubble vaporized, and the thermometer's reading dropped.

3. What do "cool" and "lower" mean?

Evaporation absorbs heat.

Factors that affect the speed of liquid evaporation:

The speed of liquid evaporation is related to the temperature of the liquid, the size of the liquid surface area and the speed of air flow near the liquid surface.

application:

Evaporation is closely related to our lives. Sometimes we should try to speed up evaporation, and sometimes we should try to slow down evaporation. Can you give specific examples to illustrate this?

hair dryer

1. How does a hair dryer make wet hair dry quickly?

Speeds up the air flow, thereby speeding up the evaporation of water.

2. What other methods can a hair dryer use to quickly dry wet hair?

Use a hot air switch to increase the temperature and speed up evaporation.

practise:

1. Wet clothes will dry out after a period of time. This is actually the ______ process of water. It is a kind of ______ phenomenon in the change of physical state. It can be carried out at ______ temperature.

2. When people come out of the swimming pool and are blown by the wind, they feel very cool. This is due to ______________. A glass of alcohol at 40℃ will continue to evaporate when the lid is opened, and the remaining alcohol temperature will be ______40℃ (fill in: above, below or equal to).

3. Fans make you feel cool in summer. This is because ( )

A. The wind blowing from the fan is cool

B. The wind blew away the heat from the body

C. The wind from the fan can speed up the evaporation of sweat and accelerate the absorption of heat from the human body.

D. Fans can lower the air temperature

4. A large number of facts show that ______ heat is required when a liquid evaporates, so evaporation has a ______ effect.

5. The phenomenon of a substance changing from a liquid state to a ______ state is called vaporization. There are two forms of vaporization: ______ and ______.

6. Which of the following statements has nothing to do with the evaporation speed of liquid ( )

A. The higher the temperature of the liquid, the faster it evaporates

B. The more mass of liquid, the faster it evaporates

C. The larger the surface area of ​​the liquid, the faster it evaporates.

D. The faster the air flows on the liquid surface, the faster it evaporates.

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Update Time: 2024-11-22

This template belongs to Physics courseware People's Education Edition Physics for Grade 8, Volume 1 industry PPT template

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