2. THE KINETIC PARTICLE THEORY

Talking book

Video 3: Kinetic Theory of Matter experiment

In the lab, we put a small amount of potassium permanganate into a beaker of water. Look at the photos to see what happens. In the top row, the water in the beaker is cold and in the bottom row, the water is hot.

If we look very closely, we can see that the particles behave in very different ways depending on the temperature of the water. It looks like the water molecules in the beaker with hot water are moving, which makes the potassium permanganate dissolve faster.

This phenomenon is the basis for the Kinetic Particle Theory (also called the Kinetic Theory of Matter) which states:

Matter is composed of particles, invisible to the naked eye, that are in some way attracted to each other (have cohesive force).
These particles are in constant motion. As the temperature rises, the speed of the particles increases.

In solids, the particles are very close together. As a result, the forces of attraction are very strong and they have a fixed position in which they can vibrate but cannot move.

In liquids, the particles are close together. The forces of attraction are not as strong as in solids, which means they can move more and vibrate. As a result, liquids can flow, change shape and are penetrable.

In gases, the particles are far apart. The forces of attraction are very weak, which means they can move freely. As a result, gases occupy all the space available in a container and take its shape.

The state of matter depends on how close together (or aggregated) the particles are. So we talk about the state of aggregation of matter.

Video 4: Particle arrangements in a solid, a liquid and a gas

Understand

Activity 3

Apply

Activity 4

Analyse

Activity 5

Fill in the blanks to explain why solids have a fixed shape and a constant volume.

In order for solids to be able to change shape and volume, their particles would need to be able to move. The particles in have a position. They can but not , so they always have the same shape and .

Why can we compress gas contained in a syringe but we can’t do the same with a syringe filled with water? Complete the explanation applying the Kinetic Particle Theory.

The particles in are still quite together, so we can’t reduce the space between them. The particles in are very far apart, so when we apply a bit of force on the syringe we can compress a lot of between them.

At a microscopic level, why is the density of solids only slightly greater than the density of liquids but the density of liquids is considerably greater than the density of gases? Complete the explanation.

The particles in are very close together, with very little space between them. This means that, in a given , there are a lot of particles, and therefore solids have a high . The forces of are not as strong in liquids when compared to solids, so even though their are close together, they are not as close as in solids. Therefore, have a high density, but not as high as in solids. The particles in are very far apart from each other when compared to liquids, with a lot more between them. This means that, in the same volume, the density of gases is considerably than in liquids and solids.

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