Kinetic Molecular Theory of Gas | Chemistry Grade XI

Kinetic Theory of Gas

Kinetic Molecular Theory of Gas | Chemistry Grade XI

Kinetic Molecular Theory of Gas

KINETIC MOLECULAR THEORY OF GAS
The model which explains the kinetic and molecular behavior of gas molecules is called kinetic molecular theory of gas. Simply, it is also called as kinetic theory of gas. It was put forward by Bernoulli in 1738. This theory was further extended by other scientists like Clausius, Maxwell, Boltzmann.

The main assumptions / postulates of kinetic theory of gas are;

  1. Gas consists of large number of extremely tiny particles called molecules. Volume of a molecule is negligible as compared to the volume of gas.
  2. The molecules of gas are in the state of continuous random motion in all possible directions in a straight path.
  3. Molecular collision of gas is perfectly elastic i.e. there is no loss of energy during collision of molecules with one another and on the wall of the container.
  4. The pressure exerted by gas molecules is due to collision of gas molecules with each other and on the wall of the container.
  5. The intermolecular force of attraction and repulsion between molecules of a gas is negligible.
  6. The average kinetic energy of gas molecules is directly proportional to the temperature in Kelvin scale.
  7. There is no effect of gravity on the molecules of gases.
JUSTIFICATION OF BOYLE’S LAW ON THE BASIS OF KINETIC THEORY OF GAS
According to the kinetic theory of gas, when gas molecules collide on the wall of the container, they exert pressure. At constant temperature, kinetic energy and average velocity remain constant. At constant temperature, if the volume is increased, the number of molecules per unit volume decreases. As a result, the number of collisions per unit time decreases. So, the pressure of gas decreases. Similarly, if volume is decreased, the number of molecules per unit volume increases . as a result, number of collisions per unit time increases. Meanwhile, pressure also increases. This is the statement of Boyle’s law.
 
JUSTIFICATION OF CHARLE’S LAW ON THE BASIS OF KINETIC THEORY OF GAS
According to kinetic theory of gas, when temperature is increased, kinetic energy and average velocity also increases. That means,when temperature increases, gas molecules collide on the wall of the container more vigorously and frequently. So the pressure of the gas increases. To keep the pressre constant, volume of the gas must be increased. It justifies that volume of gas increases with the increase in temperature at constant pressure.

According to kinetic theory of gas, the force of attraction between gas molecues is negligible. That means if the mixture of non-reacting gases is taken, they behave independently. The molecules collide on the wall of the container in the same manner as if they are present alone in the container and exert pressure. This leads to the conclusion that the total pressure exerted by the gas is the sum of the partial pressure exerted by each gaseous molecules. This is Dalton’s law of partial pressure.

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