what is kinetic theory of gas? Explained in detail.

Introduction:

Kinetic theory of gas was developed by Maxwell, Boltzmann and others in the nineteenth century. Kinetic theory of gas attempted to explain the behaviour of gases on the basis of cumulative behaviour of molecules, constituting the gaseous system. It is based on the idea that a gas is made up of rapidly and randomly moving particles which are atoms or molecules and such kind of free movement of particles is possible only when particles apply negligible force on each other. As we have already mentioned that the intermolecular forces are short range forces and those forces are important to understand the behaviour of solids and liquids, but intermolecular forces can be neglected in case of gases because intermolecular separation is too large. Kinetic theory of gases is widely accepted and has been remarkably successful in explaining many aspects related to the gases. 

Kinetic theory of gases is based on the some of the important assumptions:

Kinetic theory of gases is based on certain assumptions which basically helps in simplifying the mathematical treatment. Although these assumptions are not strictly true in many real situations but still this model is very much useful in predicting the behaviour of gases. Some of the important assumptions are listed as below:

• There are several types of gases and the molecules of different gases are different from each other but all the molecules of a particular gas are exactly identical in terms of mass and shape 

• Molecules of the gas are treated almost like point mass with no size. We can say that the size of the gas molecules is extremely small in comparison to the intermolecular distance. Actual volume occupied by those molecules in space is negligible in comparison to the total volume of the gas. 

• Molecules of gas are extremely small particles but can be treated like classical objects; hence they follow Newton's law of motion. These molecules of gas are always in a state of random motion and they move with different possible velocities in all possible directions. 

• Molecules of gas are uniformly distributed within the volume of container. Number of molecules per unit volume of gas us extremely large and this molecular density remains uniform throughout the volume of gas. 

The main postulates of kinetic theory of gas are: 

• All gases are made up of a very large number of minute particles(atoms and molecules).

• The molecules are separated from one another by a large distance. The empty spaces among the molecules are so large that the actual volume of the molecules is negligible as compared to the total volume of the gas. 

• There are no forces of interaction (attractive and repulsive) between molecules at ordinary  temperature and pressure. They move completely independent of one another. 

• The pressure exerted by the gas  is  due to the collision of its molecules on the walls of the container per unit area.

• The average kinetic energy of the gas molecules is directly  proportional to the absolute temperature. 

Kinetic theory of gas and it's equation:

on the basis of postulates of kinetic molecular theory, an equation was derived for the pressure of the gas. The equation is known as kinetic gas equation and is given as:

                   pV   = 1/3m Nu²

Where  N  is the number of molecules in volume  V  , m is the mass of a molecule and  u  is the velocity(know as root mean square velocity) of the molecules.