Physics XI Notes for Physics Notes

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Kinetic Molecular Theory Of Gases

Main postulates

  • Main postulates of kinetic molecular theory of gases are as under:
  • A gas consists of very small microscopic particles called ‘molecules’. Depending upon the nature of gas each gas molecule may consists of an atom or group of atoms. Molecules are in a state of continuous motion.
  • All the molecules of a gas are in stable state and are considered identical.
  • Any finite volume of a gas consists of very large number of molecules. At S.T.P. there are 3 × 1025 molecules in a cubic meter.
  • The molecules are wide separated from each other as compared to their own dimensions.
  • The diameter of a molecule is about 3 x 10-10 meter.
  • Gas molecules move in straight line in all possible directions (random movement) with various speeds.
  • Gas molecules collide with each other and with the walls of container. Their collisions are perfectly elastic in nature.
  • Gas molecules when collide with the walls of container, they transfer their momentum which appears as pressure of gas.
  • Molecules of an ideal gas exert no force of attraction or repulsion on one another except during collision.
  • The average kinetic energy of gas molecules is directly proportional to absolute temperature.
  • At a given temperature, the molecules of all gases have the same kinetic energy.
  • Newtonian mechanics is applicable to molecular motion.

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