"Thermal Motion of Molecular" Heat and Energy PPT Courseware

"Thermal Motion of Molecular" Heat and Energy PPT Courseware

1. Matter is composed of molecules

If you break the cup, the shards will still be glass.

After being divided many times and even ground into powder, the particles become smaller and smaller. If the points continue to be divided, is there a limit?

The smallest particles that retain the original properties of matter are called molecules

Is the molecular size very small?

The molecular volume is very small. The diameter of each molecule is about 10-10m. There are about 2.7×1019 molecules in 1cm3 of air. Now large computers can perform 10 billion operations per second. If the speed of counting people reaches 10 billion operations per second, it will take It would take 80 years to count them all.

2. Molecules are constantly moving irregularly.

Are molecules moving or stationary? Can we observe directly? How do you know if a molecule is moving?

Experiment 1． Open a bar of soap and we can smell the fragrance

Experiment 2. Diffusion of nitrogen dioxide

Phenomenon: The color of the gas collecting bottle filled with air at the top gradually becomes darker, and the color of the gas collecting bottle filled with nitrogen dioxide gas at the bottom gradually becomes lighter. In the end, the color of the gas in the two bottles is basically the same.

What do you think is the reason for the above phenomenon?

When nitrogen dioxide and air come into contact, they enter each other.

Take a guess:

Gases, liquids, and solids all diffuse. What factors are related to their diffusion speed?

Ask a question

What are the main factors that affect the speed of diffusion?

Design and conduct experiments

Fill a beaker with half a cup of cold water, and another identical beaker with an equal amount of hot water. Use a dropper to drop a drop of red ink into the cold water and hot water at the same time. Compare the spread of red ink in two cups.

in conclusion:

The main factor that affects the speed of diffusion is: temperature

The speed of molecular motion is related to temperature. The higher the temperature, the more violent the molecular motion and the faster the diffusion.

Since the motion of molecules is related to temperature, this irregular motion is called molecular thermal motion.

3. The attraction and repulsion of interactions between molecules

Experiment: Lead blocks with smooth surfaces squeeze each other

What does this experiment show?

There is attraction between molecules

Question 1: Since molecules are moving, why do the molecules in solids and liquids not fly apart, but always come together and maintain a certain volume?

☆There is gravity between molecules

Question 2: Since there are gaps between molecules, why is it difficult to compress solids and liquids?

☆There is repulsion between molecules

Key points: When the distance between molecules is small, the force behaves as _____. When the distance between molecules is slightly larger, the force behaves as _____.

There are attraction and repulsion forces that interact between molecules.

When r=r0 gravity = repulsion

When r>r0 gravity > repulsion

When r

When r>10r0 there is no force

Basic contents of molecular kinetic theory:

1. Matter is made up of molecules with gaps between them

2. The molecules of all matter are constantly moving irregularly

3. There are both attraction and repulsion between molecules

1: Fill in the blanks

1. The physical knowledge involved in "Blooming flowers inside the wall and fragrance outside the wall" mainly involves _____.

2. Diffusion can occur in _____, _____, or _____.

3. When red ink is dropped into hot water and cold water respectively, it can be found that the hot water changes color faster than the cold water. This shows that the higher the temperature, the thermal movement of a large number of molecules in the water _____.

2. Multiple choice questions

1. Which of the following phenomena can explain that "the molecules of all substances are constantly moving irregularly" ( )

A. Spray some perfume in the room and the whole room will smell the fragrance.

B. In corners where media have been piled up for a long time, the deeper parts of the wall will also turn black.

C. When sweeping the floor in the morning, I often see dust flying indoors under the sunlight.

D. Put a piece of sugar in boiling water and the whole cup of water will become sweeter.

2. The speed of thermal motion of a large number of molecules in an object is related to the following factors ( )

A. The temperature of the object

B. The speed of the object’s movement

C. The size of the object’s density

D. The size of the object’s mechanical energy

Summary of this section

1. Basic contents of molecular kinetic theory

(1) Matter is composed of molecules

(2) The phenomenon of diffusion shows that the molecules of all objects are constantly moving irregularly.

There are gaps between molecules

(3) There are attraction and repulsion forces that interact between molecules.

2. The speed of molecular motion is related to temperature. The higher the temperature, the more violent the molecular motion and the faster the diffusion.

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