Non-interacting Classical Gas

In this chapter we study thermodynamics of classical gas of non-interacting molecules, including their internal motion, using the equilibrium phase space distribution derived in Chap.  6 . We show that, when internal motion is excluded, the thermodynamic properties of the gas, predicted by statistical mechanics, are same as those of the ideal thermodynamic gas. A useful outcome of the phase space approach is the equipartition theorem which is helpful in finding internal energy of non-interacting gas for certain types of Hamiltonians. We investigate also thermodynamic properties of non-interacting gas in the gravitational field near the surface of the earth.