# CBSE Class 11 Physics Chapter 13 Revision Notes

Chapter 13: Kinetic Theory Revision Notes

- Maxwell, Boltzman, and others developed the
**kinetic theory**in the nineteenth century. - The kinetic theory of gases explains how
**gases behave**by assuming that the gas is made up of rapidly moving atoms or molecules. **Optimum Gas**: A perfect gas or ideal gas is one that strictly follows gas laws such as**Boyle’s law, Charle’s law, Gay Lussac’s law**, and so on.- The characteristics of an ideal gas are as follows:

**(i)** An ideal gas molecule is a point mass that has no geometrical dimensions.

**(ii)** There are no forces of attraction or repulsion between the gas molecules.

**Gas Pressure and Kinetic Theory**

The pressure of a gas is the result of the gas molecules constantly bombarding the container’s walls. The pressure P exerted by an ideal gas is given by

**Boyle’s Law**

The volume (V) of a fixed mass of a gas is inversely proportional to the pressure (P) of the gas if the temperature of the gas is kept constant, according to this law.

**Charles’s Law**

The volume (V) of a given mass of a gas is directly proportional to the temperature of the gas if the pressure of the gas remains constant, according to this law.

**Gay Lussac Law (or Pressure Law)**

The pressure P of a given mass of a gas is directly proportional to its absolute temperature T, provided the volume V of the gas remains constant, according to this law.

**Equation of State of a Gas**

This is the relationship between pressure P, volume V, and absolute temperature T. The state equation of an ideal gas

**PV = nRT**,

where n is the number of moles of the enclosed gas and R is the universal molar gas constant, which is R = 8.315 JK^{-1} mob^{-1} for all gases.

**Avogadro’s Law**

Under S.T.P., equal volumes of all gases contain the same number of molecules, 6.023 x 1023.

**Graham’s Law of Gas Diffusion**

The rate of diffusion of a gas is inversely proportional to the square root of the gas’s density, according to this formula.

As a result, the slower the rate of diffusion, the denser the gas.

**Dalton’s Law of Partial Pressure**

The resultant pressure exerted by a mixture of non-interacting gases is equal to the sum of their individual pressures, according to this law.

P = P1 + P2 + ————-Pn, for example.

- The arithmetic mean of the speeds of gas molecules is defined as the
**mean**(or average) speed of gas molecules.

**Temperature Kinetic Interpretation**

The absolute temperature is proportional to the total average kinetic energy of all the molecules in a gas (T). As a result, a gas’s temperature is a measure of the average kinetic energy ‘IT of the gas’s molecules.

**RT = 3/2 U**

The average kinetic energy U is zero at T = 0, according to this interpretation of temperature, implying that molecular motion ceases completely at absolute zero.

**Degrees of Liberation**

Degree of freedom refers to the total number of independent coordinates required to specify a molecule’s position or the number of independent modes of motion possible with any molecule.

The number of degrees of freedom in monoatomic, diatomic, and polyatomic (N) molecules is 3,5 or (3 N-K), where K is the **number of constraints** (structure-related restrictions).

**The Law of Energy Equipartition**

The energy of a dynamic system in thermal equilibrium is distributed evenly among the various degrees of freedom, and the energy associated with each degree of freedom per molecule is 1/2 kT, where k is the Boltzman constant.

**Path of Least Resistance**

The average distance traveled by a molecule in a gas between two successive collisions is known as its mean free path.

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