"Thermal Motion of Molecules" Internal Energy PPT Courseware 2

"Thermal Motion of Molecules" Internal Energy PPT Courseware 2

learning target

1. Know that matter is composed of molecules, and the molecules of all matter are constantly moving irregularly.

2. Be able to identify diffusion phenomena and explain them from the perspective of molecular thermal motion.

3. Know the relationship between the speed of molecular thermal motion and temperature.

4. Know that there is repulsion and attraction between molecules.

Self-study guide one

Carefully read the contents of textbook P2 to the first paragraph of P3, and answer the following questions.

1. The composition of matter

2. Size of molecules

Self-study test one

1. Which of the following statements is correct ( )

A We can see individual molecules using a magnifying glass

B molecules are the smallest particles that make up matter

C molecules are the smallest particles that maintain the original properties of matter

D A particle of dust contains dozens of molecules

2. Mix water and alcohol with volumes V1 and V2 respectively, and find that the total volume of the mixed liquid is V total ____ (optional ">", "<" or "=") V1 + V2. This experiment shows that the liquid There are ________ between molecules

Matter is composed of molecules and atoms

The diameter of a molecule is only on the order of 10-10m, so the number of molecules in an object is huge. Modern large computers can calculate 10 billion (1010) times per second. If people could count at that speed, it would take more than 80 years for a person to finish counting the molecules in 1cm3 of air!

Molecules are small in "size" but large in "number"

There are gaps between molecules

Self-study guide 2

Read the textbook P3 content carefully,

1. Why do you immediately smell the fragrance when you open a box of soap? What goes into your nose? What is the reason for the fragrance?

2. In the gas diffusion experiment in Figure 13.1-2 of the textbook, why is it that the denser nitrogen dioxide is placed under the less dense air? Can it be reversed? What does this experiment illustrate?

3. In the liquid diffusion experiment shown in Figure 13.1-3 of the textbook, the interface between the copper sulfate solution and clean water gradually became blurred after 30 days. What does this experiment show?

4. The lead and gold sheets pressed together will penetrate each other to a depth of about 1mm after being placed for 5 years. What does this experiment show?

Observation and Thought 1: Gas Diffusion

Discussion: What does the darker color in the air bottle mean? What does the lighter color in the nitrogen dioxide bottle mean? What is the reason?

Conclusion: Gas molecules are constantly moving

Observation and Thought 2: Liquid Diffusion

Discussion: What does the blurring of the interface mean? What does the darker color of the water mean? What is the reason?

Conclusion: Liquid molecules are constantly moving

induction

Solids, liquids, and gases all have this phenomenon:

Diffusion phenomenon - when different substances come into contact with each other, they will enter each other. In physics, this phenomenon is called diffusion phenomenon.

Think: What does the diffusion phenomenon indicate?

Conclusion 1: The molecules of all objects are constantly moving irregularly

Self-study test two:

1: Some of the following phenomena are diffusion phenomena ( )

A. In the golden autumn of August, the campus is filled with the fragrance of sweet-scented osmanthus.

B. Put sugar into a glass of water and the water becomes sweeter

C. Smoke comes out of the chimney

D. When sweeping the floor, dust flies in the air

E. The stains dripping on the floor tiles become more difficult to clean as time passes.

F. Mothballs will become smaller if left for a long time and eventually disappear.

G. After wiping the blackboard, chalk dust fell one after another

2. Mix 10ml of water and 10ml of alcohol thoroughly. After mixing, the total volume of water and alcohol will be ___20ml. The above phenomenon shows that there is ________ between molecules.

3. What other examples are there in life:

illustrate

There are both attraction and repulsion between molecules, and they work together. (Assume normal spacing between molecules = R)

(1) When the distance is < R (such as a compressed object), the repulsive force is greater than the gravity, which means that the repulsive force plays a major role and hinders further approach.

(2) When the distance is > R (such as an elongated object), the gravitational force is greater than the repulsive force, and the gravitational force plays the main role, preventing one from moving further away.

(3) Spacing = R (no force), when repulsion and attraction are equal, it is in an equilibrium position.

Self-study test four

1: Two pieces of lead with clean and flat surfaces can be joined together by pressing them tightly. Two broken pieces of glass cannot be put back together no matter how hard you apply them. The reason is ()

A. There is attraction between lead molecules but no repulsion.

B. There is repulsion between glass molecules, but no attraction.

C. The attraction and repulsion between molecules exist at the same time, but the distance between the two lead molecules can be so close that the attraction is greater than the repulsion.

D. None of the above statements are correct

2. Please provide a reasonable explanation based on the following phenomenon.

1) Phenomenon: Iron wire is difficult to stretch; explanation:

2) Phenomenon: It is difficult to compress the iron block by hand; explanation:

3) Phenomenon: Metal fracture can be achieved through high-temperature welding; explanation:

Summarize

1. Molecular kinetic theory

1. Matter is composed of molecules and atoms.

2. Molecules are constantly moving irregularly (diffusion phenomenon)

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 random motion of molecules.

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