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Kinetic Theory


It's known that kinetic theory is all about the energy a body possesses by the virtue of its motion. The kinetic theory of gases tells about the microscopic behavior of molecules and its interactions. There are various parameters like temperature and pressure tells about macroscopic properties of gases. They are related to molecular motion which is again a microscopic phenomenon. Hence this theory of gases relates between macroscopic properties and microscopic phenomena.

Using the observed facts of the gaseous state Maxwell, Boltzmann and Clausius gave a theory. It is known as "Kinetic Molecular Theory" or "Kinetic Molecular Theory definition" of gases. Here the assumptions of the theory are based on atoms and molecule level so it is the microscopic visualization of the gaseous state.

Kinetic theory Assumptions

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The kinetic theory of gases was given by James Clerk Maxwell, Ludwig Boltzmann and Clausius. Also called as Kinetic Theory Definition. These are postulates of kinetic theory:
  • Gases are made up of tiny discrete particles called molecules. Molecules in a gas are very far apart so that the space between each is in the orders of magnitude greater than the diameter of the molecules.
  • The molecules move randomly in all the directions with high velocities.Collisions with each other or with the walls of the container, change the direction of the movement of these molecules .
  • The gas molecules are very much apart from each other.The volume of molecules is negligible compared to the volume of the container.Molecules are electrically neutral and do not have attractions or repulsions between them .
  • The molecular collisions are perfectly elastic.It means that there is no change in the total kinetic energy during the collisions of molecules with each other or with the walls of the container . But there can be transfer of energy among the colliding particles .
  • Pressure exerted by a gas is due to the collisions of molecules made on the walls of the vessel . There is no loss of energy in these collisions .
  • Even though molecules have different velocities, their average kinetic energy is directly proportional to the absolute temperature T of the gas.
Average kinetic energy $\propto$ T

Gases which follow the postulates of the kinetic molecular theory are ideal gases . Most of the common gases do not behave as ideal gas. Real gases approach ideal gas behavior at low pressures and high temperatures.

Kinetic theory of Matter

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Kinetic theory of matter tells that matter is made of particles moving freely in constant motion. It predicts how matter behaves depending on certain assumptions and approximations.The assumptions are made to avoid theory from making it complex.