"Vaporization and Liquefaction" PPT Courseware on Changes in State of Matter 10

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"Vaporization and Liquefaction" PPT Courseware on Changes in State of Matter 10

Think about it, do it

Place a few drops of alcohol in a clear plastic bag;

Squeeze the bag, drain out the air, and tie the mouth tightly with a rope;

Then put it into hot water above 80℃.

What changes will you see?

Remove the plastic bag from the hot water

What will happen after a while?

learning target

1. What is vaporization? liquefaction?

2. What is boiling? Characteristics of boiling? What conditions are needed for boiling?

What is boiling point? What factors affect boiling point?

3. What is evaporation? What are the characteristics of evaporation? What factors are related to the speed of evaporation? Can you give examples of speeding up evaporation and reducing evaporation?

How many ways are there to vaporize?

4. What is liquefaction? How many methods are there for liquefaction? Can you give an example?

5. Are vaporization and liquefaction exothermic or endothermic respectively?

1. Boiling

Concept: Violent vaporization occurs simultaneously inside and on the surface of a liquid at a certain temperature.

Ask a question

What are the characteristics of water when it boils?

If you continue to heat water after it boils, will the temperature get higher and higher?

analysis and argumentation

Summary of experimental phenomena

The bubbles are small before boiling and become larger during boiling.

The sound is louder before boiling and becomes quieter when boiling.

Characteristics of boiling: The temperature rises before boiling. When water reaches a certain temperature, it boils and the temperature remains unchanged.

Turn off the heat and stop boiling.

2. Evaporation

Wet clothes in the sun will dry even if the temperature does not reach the boiling point of water.

concept:

A slow vaporization phenomenon that occurs only at the surface of a liquid at any temperature.

think about it

What factors are related to the speed of evaporation?

(1) Clothes dried faster in summer than in winter.

(2) Clothes will dry faster if they are spread out to dry than if they are piled together.

(3) Clothes dry faster when there is wind than when there is no wind.

in conclusion

The higher the temperature of the liquid, the faster it evaporates;

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

The faster the air moves over the liquid surface, the faster it evaporates.

Can you give examples of speeding up evaporation and reducing evaporation?

3. Evaporative refrigeration

1. Rub alcohol on the back of your hand. How does it feel?

There is a cold feeling on the back of the hand.

The evaporation of the alcohol absorbs heat from the back of the hand and its surroundings.

2. Apply alcohol to the glass bulb of the thermometer repeatedly and fan it with a fan. What will happen to the thermometer reading?

If you do not apply alcohol on the thermometer and fan it with a fan, will the thermometer reading change?

①The thermometer reading first drops and then rises.

②The thermometer reading remains unchanged.

think about it

Being burned by 100℃ water vapor is much more serious than being burned by 100℃ water. Why?

Because water vapor needs to release heat to liquefy.

discuss

When the water in the kettle boils, why can't the "white gas" be seen in the section near the spout, but can be seen in the section above?

The temperature near the spout is higher and the water vapor is not liquefied, while the temperature of the water vapor in the back section is lower and liquefies into small water droplets, so it can be seen.

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For more information about the PPT courseware "Changes in the State of Matter, Vaporization and Liquefaction", please click on the Changes in the State of Matter ppt, Vaporization and Liquefaction ppt tab.

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Update Time: 2024-11-22

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