The kinetic theory helps to explain the way in which matter behaves. The evidence is consistent with the idea that all matter is made up of tiny particles. The kinetic theory explains:
- The states of matter
- the differences in the properties of solids, liquids and gas
- The changes of state
Solids have a fixed shape and volume
The particles in a solid are arranged in a fixed pattern or lattice. Strong attractive forces hold them together. They have enough kinetic energy to vibrate and rotate about their fixed positions. For this reason, they have a fixed shape. Since the particles in solid are already very close to each other they cannot be compressed. Thus, a solid has a definite volume.
Liquid does not have a fixed shape but a fixed volume
The particles in a liquid arranged in a disorderly manner can move about and slide past each other. The forces that hold them together are weaker than in a solid. They are still close together, but not in a lattice.
That is why liquid does not have a fixed shape. The particles in a liquid are farther away from one another than that of in solids. However, the particles are still packed quite closely together here. Thus a liquid cannot be compressed and has a fixed volume.
Gas does not have a fixed volume and a fixed shape
The particles in a gas have a lot of kinetic energy and are not held in fixed positions. They are far apart, and they move about very quickly. They collide with each other and bounce off in all directions. There is a very weak force of attraction between them. For this reason, they have no fixed shape. The particles in a gas have a lot more space between them than those of in solids or liquid. In other words, the particles can be forced to move closer together. Since the gas can be compressed, it does not have a fixed volume.