Diffusion

Diffusion

Let us place a book on a table. Let it not be disturbed. Observe for five minutes.

Now take a glass of water and add just a drop of ink carefully at the centre. Do not shake or stir.

Now light an incense stick and keep in one corner of the room.

Let us answer the following questions.

Did the book move?

Did the ink particles move and spread itself in the water? How long did it take for complete mixing?

Did you get the smell of the incense stick from where you are standing?

How fast did you get the smell? How did the smell reach you?

We may conclude that the particles of gases and liquids can move and that among gases more easily. We call this movement as diffusion. Diffusion is the tendency of particles to spread out in order to occupy the available space.

Fact files

Movement of particles is restricted in solids and they do not diffuse like liquids or gases. In fluids the particles are under motion and hence can push ink or smoke particles here and there.

Activity 4

Lift an uninflated cycle tube. Inflate it and lift it again. Is there a change in the weight? Can we see that air has mass?

So we can say that air is also matter though we cannot see.

Let us try to know more about matter.

Test Yourself

Name an object which is brittle and transparent.

Name an object which can be stretched.

Name two objects which can be bent.

Activity 5

Let us take two sachets of juice. In both the sachets, it is written 100ml. Let us empty two sachets and pour the juice into the following glasses.

Does its shape also change? Yes / No

Answer: Yes

Does its volume change? when it is poured into a big glass or a small one? Yes / No

Answer: No

How will you find out whether the volume has changed or not?

Answer: A liquid needs a container and takes the shape of a container because the particles slide past one another and keep moving. The amount of juice is the same in both glasses. The volume of a liquid remains the same whether it is kept in a large container or a small one but its shape changes.

A liquid needs a container and takes the shape of a container because the particles slide past one another and keep moving. The amount of juice is the same in both glasses. The volume of a liquid remains the same whether it is kept in a large container or a small one but its shape changes.

Try to draw the shape of the liquid containers alone in your note book. What do you observe?

Answer: Its shape changes.

Think to learn

Solid → Liquid → Gas

“Liquefaction of gases” is the process by which substances in their gaseous state are converted to the liquid state. When pressure on a gas in increased, its molecules comes closer together, and its temperature is reduced, which removes enough energy to make it change from the gaseous to the liquid state.