Kinetic Molecular Theory of Gases

Theory

In kinetic molecular theory, a gas is modeled as a collection of particles in constant motion. A single particle moves in a straight line until it collides with another particle or with the wall of the containe. The kinetic molecular theory is based on following postulates or assumptions:

1.  The size of a particle is negligibly small. Under normal pressure, the space between atoms or molecules in a gas is very large compared to the size of an atom or molecule itself. So, the actual volume of gas molecules is negligible in comparison to the total volume of the gas.

2.  The average kinetic energy of a particle is directly proportional to the absolute temperature (that is temperature in kelvins).  The motion of atoms or molecules in a gas is due to thermal energy. So, as the temperature increases, the energy of the molecules also increases.3.  The collision of one particle with another (or with the walls) is completely elastic. 

When the molecules collide with each other, there is complete transfer of energy from one molecule to another. Thus, the total energy of the molecules remains same before and after the collision. There is no net loss of energy. Therefore, the motion of molecules do not cease and they never settle down.

4. There is no force of attraction between the gas molecules, because the distance between the molecules is very large. Therefore, the gases can easily expand.

5. Particles of the gas are in constant motion.

6. Different particles of the gas have different speeds. Although initially they may have same speed, but due to collisions with each other, the speed of the particles change.