"Exploring the Characteristics of Vaporization and Liquefaction" Material Forms and Their Changes PPT Courseware 2

Description

"Exploring the Characteristics of Vaporization and Liquefaction" Material Forms and Their Changes PPT Courseware 2

learning target

1. Able to distinguish between solid, liquid and gaseous states of matter. Know what vaporization and liquefaction are. Know that vaporization absorbs heat and liquefaction releases heat

2. Know what evaporation is and the factors that affect evaporation speed

3. Know the boiling phenomenon and characteristics of boiling, and know what the boiling point is

4. Be able to use the knowledge of vaporization and liquefaction to explain related simple thermal phenomena

Core test points: Judgment of vaporization and liquefaction phenomena, the relationship between the boiling point of water and atmospheric pressure.

Preview before class

1. Vaporization: The process in which a substance changes from ________ to ________ is called vaporization. The methods of vaporization include ________ and ________. It’s all _____ hot.

2. Evaporation: It is a ________ vaporization phenomenon that can be carried out at ________ temperature and only occurs in liquid ________. When evaporating, it absorbs heat from the surroundings so that the temperature of itself and the surroundings is ________, so it has the function of ________.

3. Boiling: It is the vaporization phenomenon of ________ that occurs simultaneously between liquid ________ and ________ at ________ temperature. When a liquid boils, it must be ________, but the temperature must be ________. This temperature is called _________.

4. Factors that affect the speed of liquid evaporation: (1) liquid __________; (2) liquid __________; (3) liquid surface __________ speed.

5. Liquefaction: The process in which a substance changes from _______ to _______ is called liquefaction. Liquefaction requires ____ heat. Methods of liquefying gases include: _______ and _______.

Lectures in class

Knowledge point 1. The form of material existence

Solid, liquid and gaseous states are the three common states of matter in nature. For water, they are: solid ice, liquid water and gaseous water vapor. The three states of matter and their characteristics are shown in the following table:

[Example 1] The ice cubes placed in the beaker gradually turn into _____ state of water during the heating process. When the heating is continued, the _____ state water turns into _____ state of water vapor. It can be seen from this that, The form in which matter exists is related to the _____ of the matter.

[Exercise 1] Water is in the _____ state at room temperature. The other two states it exists in nature are solid _____ and gaseous _____.

Knowledge point 2. A way of vaporization-evaporation

(1) The change of a substance from a liquid state to a gaseous state is called vaporization, and vaporization requires the absorption of heat.

(2) Ways of vaporization: evaporation and boiling.

Evaporation is a slow vaporization phenomenon that can occur in liquids at any temperature and only occurs on the surface of the liquid.

The liquid absorbs heat during the evaporation process, causing the temperature of the liquid and the objects it is attached to to drop, which has a cooling effect.

Factors that affect evaporation speed:

(1) The temperature of the liquid, the evaporation speed of the liquid is related to the temperature of the liquid. The higher the temperature, the faster the evaporation.

(2) The surface area of ​​the liquid. The larger the surface area of ​​the liquid, the faster it evaporates.

(3) How fast the air flows on the liquid surface. The faster the air flows on the liquid surface, the faster it evaporates.

Therefore, to speed up the evaporation of liquid, the measures that should be taken are: increase the temperature of the liquid, increase the surface area of ​​the liquid, and speed up the flow of air on the surface of the liquid. To slow down the evaporation of a liquid, the measures that should be taken are: lower the temperature of the liquid, reduce the surface area of ​​the liquid, and slow down the flow rate of air on the surface of the liquid.

Knowledge point 3. Another way of vaporization-boiling

Boiling is a violent vaporization phenomenon that occurs simultaneously on the surface and inside of a liquid.

Water boiling experiment:

Before boiling, bubbles form inside the liquid and gradually become smaller as it rises. As a result, they disappear before reaching the liquid surface; when boiling, the bubbles gradually become larger as they rise, and burst after reaching the liquid surface.

When a liquid boils, it absorbs heat and the temperature remains constant. The temperature at which a liquid boils is called the boiling point. Different liquids have different boiling points, and the boiling points of the same liquid are related to atmospheric pressure. As the air pressure increases, the boiling point increases. At 1 standard atmospheric pressure, the boiling point of water is 100°C.

Conditions for boiling to occur: a. The liquid temperature reaches the boiling point; b. The boiling process needs to continue to absorb heat.

Boiling image: As shown in the figure, it vividly and intuitively displays the characteristics of the boiling phenomenon.

Note: (1) It is usually said that the boiling point of water is 100°C, which refers to the boiling point of water under 1 standard atmosphere. Different air pressures on the water surface lead to different boiling points of water.

(2) Household pressure cookers are made by increasing the air pressure and raising the boiling point. The air pressure in the pressure cooker can reach 2 standard atmospheres, and the boiling point of water can reach about 120°C.

(3) On high mountains, the air pressure is low and the boiling point of water is low. At Mount Everest, which is 8844 m above sea level, the boiling point of water is only 72°C. At an altitude of tens of thousands of meters, the boiling point of water is only a dozen degrees Celsius. Therefore, it is not surprising that the "boiling water" is not hot to the touch, the eggs are not cooked well, and the boiling water is not disinfected.

Knowledge point 4. liquefaction

(1) The change of a substance from a gaseous state to a liquid state is called liquefaction; the liquefaction process releases heat; liquefaction is the opposite process of vaporization.

(2) Liquefaction phenomenon:

①After the water is boiled, "white gas" is seen at the spout (water vapor evaporates out of the pot and liquefies into small mist-like water droplets when encountering cold air)

② In summer, water pipes and water tanks will "sweat". (Water vapor in the air liquefies into water droplets when cooled)

The methods of liquefaction are divided into: lowering the temperature and compressing the volume. All gases can liquefy when their temperature drops low enough. At a certain temperature, compressed volume can liquefy gas, such as liquefied petroleum gas. After gas is liquefied, its volume becomes smaller, making it easier to store and transport.

⑴Liquefaction by cooling (encountering cold, releasing heat), for example:

①The formation of fog and dew (water vapor in the air liquefies into small mist-like water droplets when cooled; attached to dust and floating in the air, forming "fog"; attached to vegetation and gathering into "dew")

② In winter, "white air" comes out of the mouth. In summer, "white gas" appears around the popsicles. (Water vapor liquefies into mist-like water droplets when cooled)

③In winter, vague "moisture" is often seen on the inside of the window. (Water vapor in the house liquefies into small water droplets when it encounters cold glass)

④When the dentist examines the patient's teeth, he bakes the small mirror used for examination slightly on an alcohol lamp and then puts it into the mouth. (Prevent the water vapor in the mouth from liquefying into small water droplets and attaching to the mirror surface when cold)

⑵Liquefaction of compressed volume, for example:

① At normal temperature, compress the petroleum gas into a cylinder and store it in the form of liquid petroleum gas

②The fuel and combustion accelerant of the "Long March" rocket are: compressed "liquid hydrogen" and "liquid oxygen"

Heat release of liquefaction:

①In the winter in the north, hot water vapor is passed through the indoor heating pipe for heating, and water is finally recovered at the other end of the pipe. (Water vapor liquefies into water and releases a lot of heat)

②1000C water vapor is more likely to burn the human body than 1000C water. (It takes heat to liquefy 1000C water vapor into 1000C water)

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"Exploring the Characteristics of Vaporization and Liquefaction" Material Forms and Their Changes PPT Courseware:

"Exploring the Characteristics of Vaporization and Liquefaction" Material Forms and Changes PPT Courseware Teaching Objectives 1. Describe the basic characteristics of the three physical states of solid, liquid and gas. List the different states of matter in nature and life and their applications. 2. Know what vaporization and liquefaction are, know vapor...

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Update Time: 2024-11-24

This template belongs to Physics courseware Guangdong and Shanghai version of eighth grade physics volume one industry PPT template

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