Molecules of gases remain in continuous motion.

Moving molecules collide with each other and with the walls of the container.

Collision of molecules of results in change of their speed and redistribution of energy.

The speed and energy of all the molecules of the gas at any instant are not the same.

Average value of speed of molecules can be determined by adding the individual and then by dividing number of molecules.

Gases consist of large number of identical particles (atoms or molecules) that are so small and so far apart on the average that the actual volume of the molecules is negligible in comparison to the empty space between them.

Gas molecules are considered as point masses.

There is no force of attraction between the particles of a gas at ordinary temperature and pressure.

Particles of a gas are always in constant and random motion.

Particles of a gas move in all possible directions in straight lines.

During their random motion, they collide with each other and with the walls of the container.

Pressure is exerted by the gas as a result of collision of the particles with the walls of the container.

Collisions of gas molecules are perfectly elastic.Elastic Collisions means that total energy of molecules before and after the collision remains same.

At any particular time, different particles in the gas have different speeds and hence different kinetic energies. If a molecule has variable speed, then it must have a variable kinetic energy. In kinetic theory, it is assumed that average kinetic energy of the gas molecules is directly proportional to the absolute temperature.