Definition Of Kinetic Molecular Theory

Definition of Kinetic molecular theory

The kinetic molecular theory is an alternative approach to understand the behaviour of gases

Conducting careful experiments is an important aspect of scientific method and it tells us how the particular system is behaving under different conditions
A theory is a model that enables us to better understand our observations
The theory that attempts to elucidate the behaviour of gases is known as kinetic molecular theory
Assumptions or postulates of the kinetic molecular theory of gases are
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
They are considered as point masses. This assumption explains the great compressibility of gases
There is no force of attraction between the particles of a gas at ordinary temperature and pressure
The support for this assumption comes from the fact that gases expand and occupy all the available space
Particles of a gas are always in constant and random motion
If the particles were at rest and occupied fixed positions, then a gas would have had a fixed shape which is not observed
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
The total energy of gas molecules before and after collision is the same
There may be exchange of energy between colliding molecules, their individual energies may change, but the sum of their energies remains constant
If there was loss of kinetic energy, then the motion of the molecules will stop and gases will settle down
At any particular time, different particles of gas have different speeds and hence different kinetic energies
This assumption is reasonable because particles have different speeds which change when they collide
It is possible to show that though the individual speeds are changing, the distribution of speeds remains constant at a particular temperature
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
On heating a gas, the kinetic energy of gas molecules increases and the molecules strike the walls of the container with higher speed

The most important advantage of liquefying gases is that they can then be stored and transported in much more compact form than in the gaseous state.
liquid oxygen and liquid hydrogen are used in rocket engines. Liquid oxygen and liquid acetylene can be used in welding operations