Kinetic Theory of Gases Class 11

There are various branches of physics and various types of topics in physics taught in class 11. One such topic is the Kinetic Theory of Gases Class 11. The kinetic theory of gases demonstrates the 3 visible features of a gas in terms of the microscopic nature of atoms and molecules forming the gas. Generally, the physical characteristics of solids and fluids can be distinguished based on their area, form, mass, volume, etc. In the case of gases, they have no distinct shape, size, and mass and volume are not directly calculable. Here, in this blog, we discuss all details about the kinetic theory of gases class 11. 

Must Read: Class 11 Physics Chapter 7 – System of Particles and Rotational Motion

What is the Kinetic Theory of Gases?

The kinetic theory of gases class 11 chapter illustrates the molecular structure of the gas in terms of the abundance of submicroscopic particles. The theory also demonstrates that gas pressure occurs because of the particles striking against each other and the surface of the vessel. The kinetic theory of gases also describes characteristics such as temperature, coherence, and thermal conductivity.

The importance of the kinetic theory is that it assists in forming a relationship between the perceptible attributes and the microscopic phenomenon. In other words, the kinetic theory of gases also assists us to analyze the behavior of the molecules. Usually, the molecules of gases are constantly in motion and they conduct strikes against each other and the surfaces of the vessels.

The kinetic theory was stated in the 19th century by Maxwell, Boltzmann, and others. Kinetic theory illustrates the reaction of gases based on the view that the gas consists of swiftly flowing atoms or molecules.

Ideal Gas

Next in the kinetic theory of gases class 11, we move on to ideal gas. An ideal gas rigidly follows gas fundamentals such as Boyle’s law, Charle’s law, Gay Lussac’s law, etc.

An ideal gas has the succeeding features:

• Molecules of an ideal gas is a point mass with no geometrical dimensions.
• There is no force of attraction or repulsion amidst the molecules of the gas.

Kinetic Theory and Gas Pressure

The pressure of a gas is the result of continuous bombardment of the gas molecules against the walls of the container. According to the kinetic theory of gases class 11, the pressure exerted by an ideal gas is given by:

Where is the density of the gas and c^-2 is the mean square speed of the gas molecules. If a container has n molecules each of mass m, then

P=13c^-2

where V is the volume of the container.

Boyle’s Law

As per Boyle’s law in the kinetic theory of gases class 11, the volume (V) of a definite mass of a gas is inversely proportional to the pressure (P) of the gas, presented the temperature of the gas is maintained constant. 

i.e.,  V∝ 1P or PV = constant

Charles’s Law

Next, we move on to Charle’s Law in the kinetic theory of gases class 11. As per Charles’s law in the kinetic theory of gases class 11, the volume (V) of a provided mass of a gas is directly proportional to the temperature of the gas, given the pressure of the gas continues to be constant.

i.e., V∝ T or VT= a constant V₁T2= V₂T2

Gay Lussac’s Law (or Pressure Law)

Moving on to the kinetic theory of gases class 11, we have Guy Lussac’s Law. As per the law of Gay Lussac or the Pressure Law, the pressure P of a provided mass of a gas is directly proportional to its absolute temperature T, given the volume V of the gas is kept constant.

I.e.,  P∝ T or PT= a constant P₁T1= P₂T2

Equation of State of An Ideal Gas

Next, the kinetic theory of gasses class11 talks about the equation of the state of an ideal gas. The relation among pressure P, volume V and absolute temperature T of a gas is called its equation of state. The equation of state of an ideal gas

PV = nRT

where n is the number of moles of the contained gas and R is the molar gas constant which is alike for all gases and its value is

R = 8.315 JK-1 mob-1

Avagadro’s Law

Avogadro’s Law is also important in the kinetic theory of gases class 11. Equal amounts of all gases under standard temperature and pressure, contain the same number of molecules comprising 6.023 x 1023 molecules.

Graham’s Law of Diffusion of Gases

We further move on to Graham’s Law of Diffusion of Gases in the kinetic theory of gases class 11. It says that the rate of diffusion of a gas is inversely proportional to the square root of the density of the gas. 

i.e.,  r∝ 1

Therefore, the denser the gas, the more passive is the rate of diffusion.

Dalton’s Law of Partial Pressures

Dalton’s Law of Partial Pressures is also an important topic in kinetic theory of gases class 11. As per this law, the net pressure applied by a mix of non-interacting gases is equivalent

to the sum of their pressures.

i-e., P = P1 + P2 + ————-Pn

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

I.e., mean speed, _mean = _nn= 8KBT/m

 Where m is the mass of 1 molecule of given gas and T= temperature of the gas.

The root mean square speed of gas molecules is defined as the square root of the mean of the squares of the speeds of gas molecules.

The most probable speed of gas molecules is defined as the speed which is possessed by the maximum number of molecules in a gas.

Kinetic Interpretation of Temperature

The total average kinetic energy of all the molecules of a gas is proportional to its absolute temperature (T). Thus, the temperature of a gas is an estimate of the average kinetic energy of the molecules of the gas.

U = 3/2 RT

As per this understanding of temperature, the average kinetic energy U is zero at T = 0, i.e., the movement of molecules halts altogether at absolute zero.

Also Read: Physics Syllabus For Class 11

Degrees of Freedom

The entire number of free coordinates needed to define the location of a molecule or the number of autonomous forms of motion achievable with any molecule is called the degree of freedom.

Mono-, di-, and polyatomic (N) molecules have, 3,5 or (3 N-K) number of degrees of freedom where K is the number of limitations.

Law of Equipartition of Energy

For a dynamic system in thermal equilibrium, the energy of the system is evenly distributed amongst the different degrees of freedom and the energy linked with every degree of freedom per molecule is 1/2 kT, where k is Boltzmann constant.

Mean Free Path

The mean free path of a molecule in a gas is the average distance covered by the molecule between 2 consecutive collisions.

• Smaller the number of molecules per unit volume of the gas, the larger is the mean free path.
• Smaller the diameter, the larger is the mean free path.
• Smaller the density, the larger is the mean free path. In the case of vacuum, ρ = 0, λ —>∞
• Smaller the pressure of a gas, the larger is the mean free path.
• Higher the temperature of a gas, the larger is the mean free path.

Brownian Motion

The last and another important portion in the kinetic theory of gases class 11 is the Brownian Motion. The constant arbitrary movement of microscopic particles suspended in air or any liquid is called Brownian or microscopic motion.

Brownian suspended motion in the air or any liquid is witnessed in various fluids. Brownian motion is because of the uneven bombardment of the dissolved particles by the molecules of the encircling medium.

Explore: Class 11 Physics Chapter 3 – Motion in a Straight Line

FAQs

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