The Kinetic theory is so named because it deals with that property of the particles which is so crucial in understanding the three states of matter, namely the motion of the particles. Because the particles are in constant motion, they possess kinetic energy which tends to keep the particles well spaced out in any substance. Thus in terms of kinetic theory.
1. The gaseous state is the one in which the molecule are widely separated from one another but having negligible volume. The gases are easy to compress due to large empty spaces.
2. The gas molecules are in continuous motion, traveling in straight paths between collisions, but in random directions. The average distance between collisions is the mean free path.
3. The molecules collide with one another and with the walls of container, but these collisions are perfectly elastic (result in no loss of energy).
4. Gas pressure is the result of the collision of gas molecules with the walls of the container.
5. In an ideal gas, there are no attractive or repulsive forces between molecules. Thus each molecule acts quite independently of the others.
6. The average kinetic energy of gas molecules depends upon the absolute temperature. At any given temperature, the molecules of all gases have the same average kinetic energy (1/2 mv²).
The kinetic theory was extended to account for the behavior of liquids and solids.
For a liquid, the kinetic theory suggests that the particles of a liquid are fairly randomly arranged (as in gas), but consists of ‘clusters’ in which they are very close together. This makes liquid have a definite volume, but since the particles are still fairly free to move, it does not have any definite shape of its own.
For a solid, the kinetic theory postulates that the molecules are closely packed, so that the forces of attraction between the molecules are very strong and free movement of particles can not take place. Thus in a solid, the particles are arranged in a fixed pattern and they form a lattice of vibrating masses. This makes a solid have a definite shape.