"Vaporization and Liquefaction" State of Matter and Its Changes PPT Courseware 2

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"Vaporization and Liquefaction" State of Matter and Its Changes PPT Courseware 2

question:

Where did the word "water" on the blackboard go?

Have you ever seen similar phenomena in your life?

1. What is vaporization?

The change of substance from liquid to gaseous state is called vaporization.

There are two types of vaporization: evaporation

different ways of boiling

(1) Evaporation

1. Factors affecting evaporation speed

Contacting examples in life, let us think about the factors that affect the speed of evaporation?

The temperature of the liquid.

The surface area of ​​a liquid.

Air flow over a liquid surface.

Notice:

Different liquids evaporate at different speeds under the same conditions. For example, water and alcohol evaporate faster.

2. Characteristics of evaporation

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

3． Evaporation absorbs heat

Liquids need to absorb heat during the process of vaporization.

Evaporation is a form of vaporization that also requires the absorption of heat.

Application of evaporative heat absorption.

(2) Boiling

small experiment

Observe the boiling of water and explore the pattern of temperature when water boils.

1. what is boiling

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

experiment equipment

Iron stand thermometer beaker matches table

alcohol lamp water

2. Characteristics of boiling

A liquid continuously absorbs heat as it boils, but the temperature remains constant.

We call the temperature at which a liquid boils the liquid's boiling point.

Two conditions for boiling:

a. Reach boiling point b. constantly absorbing heat

(3) Liquefaction

The process of matter changing from gaseous state to liquid state is called liquefaction.

Where does "white gas" come from?

"White gas" is not water vapor, but small water droplets formed by liquefaction of water vapor.

way of liquefying

For example: rain, dew, and "white gas" near the mouth of the pot

Water droplets on window glass in winter

Water droplets on beverage bottles taken out of the refrigerator

For example: butane gas in lighters

liquefied petroleum gas

Fuel in rockets (liquid hydrogen)

Heat is released during gas liquefaction.

1. A burn from 100°C steam is more harmful than a burn from 100°C boiling water. Why?

Answer: Because water vapor at 100°C liquefies on the skin and releases heat, people will be burned more seriously.

2 . When your hands are cold in winter, "blow" into your hands with your mouth. (Blow slowly) your hands will feel warm. If you blow hard into your hands, not only will your hands not be warmed, but they will feel colder. They are all "qi" coming out of the mouth, so why do they feel different?

Answer: When breathing, because it is relatively slow, the water vapor in the mouth liquefies and releases heat when it encounters cold hands, so people will feel warm; when blowing hard, the evaporation of the water on the hands will be accelerated, and evaporation absorbs heat. So people will feel colder.

3． When the rocket is launched, in order to protect the launch chassis, a large pool needs to be built at the bottom of the launch tower. Why? What is a white air mass?

Answer: Water absorbs heat when it vaporizes, so it can protect the launch chassis. After a large amount of water vapor leaves the water, it liquefies when it encounters cold again, so a large amount of white gas appears.

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Update Time: 2024-07-30

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