The Quantum Theory of the Equation of State

It is shown that the quantum theory analogue to the quantity e^-{kT} giving the distribution in coordinates of systems at temperature T can be easily set up. Similarly in quantum theory the computation of the free energy can be reduced to the integration of such a function over the coordinates, as in classical theory. The result is applied to a qualitative discussion of the equation of state of an imperfect gas, showing that He and H₂ may be expected to show quantum effects in their equations of state, but hardly any other gases.