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Suppose energy is the sum of two terms:

*U*=*U _{0}*+

Idea:

(25) |

(26) |

(27) |

**Van der Waals Equation of state:**- Let's consider the
*hard-sphere system as a reference*, and the attractive part of the molecular interaction*v*(*r*) as a perturbation. Assuming at low densities: For the hard spheres system: Substituting this into (26,27), and differentiating with respect to volume, obtain the Van der Waals equation of state:

© 1997

Thu Sep 25 23:59:09 EDT 1997