  We show that when the thermal wavelength is comparable to the spatial size of
a system, thermodynamic observables like Pressure and Volume have quantum
fluctuations that cannot be ignored. They are now represented by operators;
conventional (classical) thermodynamics is no longer applicable. We continue
the work in earlier papers where quantization rules for thermodynamics were
developed by analogy with optics and mechanics, by working out explicitly the
quantum theory of van der Waals gases. We find a wave equation satisfied by the
thermodynamic wave function as well as solutions ({\em coherent states}) that
are centered at the classical equations of state. The probability of departure
from the classical theory is dependent on a parameter $\sigma$ which is a
property of the gas molecule.
