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12.6 Kinetic Theory of Ideal Gases

The concept of atoms and molecules being the ultimate building blocks of bulk matter was revived by Dalton in order to explain the three laws of chemical combinations. In the mid 19th century, these concepts, together with certain assumptions regarding the nature, size, distribution and motions of the molecules and atoms, were synthesized with Newtonian mechanics, in order to explain the observed behavior of ideal gases. This work by Maxwell, Boltzman and others, led to the development of what is known as the Kinetic Theory of gases.

The assumptions of the Kinetic Theory are :

i) Any gas is made up of a very large number of molecules.

ii) Molecules of a gas are identical to each other, with respect to shape, size and mass.

iii) The molecules are perfectly rigid spheres of negligible radius.

iv) The molecules are in an incessant state of chaotic motion in all possible speeds and directions.

v) The distribution of molecules is homogenous and isotropic in any container enclosing the gas.

vi) The molecules exert force on each other only when they collide with each other or with the walls of the container.

vii) The collision between molecules or molecules and the walls of the container are perfectly elastic collisions, i.e., only such collisions can change the directions of motion but not their speeds.

viii) Between successive collisions the molecules travel freely with constant velocities; the distance travelled freely is called free path. On an average, the mean free path of all molecules is the same.

ix) The average Kinetic energy of a molecule is proportional to the absolute temperature of the gas.


12.1 Solids
12.2 Liquids
12.3 Gases
12.4 Gas Laws
12.5 Equation of State :Ideal Gas Equation
12.6 Kinetic Theory of Ideal Gases

Chapter 13

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