Kinetic molecular theory of gases

Kinetic molecular theory of gases-Average kinetic energy

The kinetic energy of gases first time developed by Bernoulli in 1738 to explain the molecular properties of gases on the basis of mechanical theory. These ideas were at the root of the theory to explain the kinetic behavior of gases. Thus in the nineteenth century, the effort of Joule, Kronig, Clausius, Boltzmann, and Maxwell, gives the formula of the kinetic theory of gases.

In the molecules or particles are held very closely together and are entirely devoid of any translatory motion. If a specific heat supplied to solid, it takes the form of vibrational motion with the rise of temperature. But with the further increases the thermal energy, the vibrational motion rises to such extent the molecules break down to transform into a liquid.

Kinetic molecular theory of gases postulates

Kinetic molecular theory of gases based upon certain postulates which use for the derivation of ideal gas law and kinetic gas equation for the calculation of gas density, molar masses, and diffusion or effusion.

  1. Gas molecules are composed of very small discrete particles. In any one gas, all the molecules are of the same size and mass, but these differ gas to gas.
  2. Within the container, the gas molecules are moving in all directions with a verity of speeds. Some are very fast while others are slow. Thus due to random motion, the gas molecules are executing two types of collisions. When it collided with the walls of the container called wall collision but with themselves called an intermolecular collision.
  3. These collisions are perfectly elastic. Thus there occurs no loss of kinetic energy or momentum of the molecules by this collision.
  4. Gas molecules are assumed to be point masses. Hence the size of the gas molecule is very small in comparison to the distance where they travel.
  5. Especially at low pressure, the gas molecules have no intermolecular attraction. Thus one molecule can exert pressure independent of the influence of other molecules.
  6. The pressure exerted by a gas is due to the uniform wall collisions. Hence higher the frequency of the wall collision greater will be the pressure of the gas.
  7. This explains Boyle’s law since when the volume is reduced at a constant temperature, wall collision becomes more frequent and pressure is increased.
  8. Through the molecular velocity constantly changing due to the intermolecular collision but the average kinetic energy of the gas molecules remains fixed at a given temperature.

When temperature raised, the molecules would move more vigorously resulting in a larger number of impacts on the wall of the container at constant volume. Thus it increases the pressure with the rising temperature at constant volume. This is Charles’s law for ideal gases.

Originally published at on April 21, 2019.

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