What are the postulates of kinetic energy of gases?

At what temperature is the root mean square speed of an atom in an argon gas cylinder equal to the r.m.s. speed of helium gas atom at –20°C? [Atomic mass of Ar = 39.9, He = 4.0]

R.M.S speed of atom is given by,

           v=3kTm = 3RTM                  ...(1)

Atomic mass of Argon, MAr=39.9,       

Atomic mass of Helium, 

Temperature, THe =-20°C = 253K,

Temperature of Argon gas, TAr=? 

                  3RTHeMHe = 3RTArMAr  

                            TAr = THeMHeMAr      = 253×39.94      =2.5×103K

is the required temperature at which r.m.s speed of an argon gas cylinder is equal to the r.m.s speed of helium gas atom.

Write Postulates of the kinetic theory of gases.

Postulates of the kinetic theory of gases:

1. Gases consist of tiny particles (molecules or atoms).
2. On average, gas molecules remain far apart from each other. Therefore, the actual volume of the gas molecules is negligible as compared to the volume of the container. Hence, gases are highly compressible.
3. The attractive forces between the gas molecules are negligible at ordinary temperature and pressure. As a result, the gas expands to occupy the entire volume of the container.
4. Gas molecules are in constant random motion and move in all possible directions in straight lines. They collide with each other and with the walls of the container.
5. Pressure of the gas is due to the collision of gas molecules with the walls of the container.
6. The collisions of the gas molecules are perfectly elastic in nature, which means that the total energy of the gaseous particle remains unchanged after the collision.
7. The different gas molecules move with different velocities at any instant and hence have different kinetic energies. However, the average kinetic energy of the gas molecules is directly proportional to the absolute temperature.

Concept: Kinetic Molecular Theory of Gases

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