Joule-Thomson effect, definition

From a fundamental perspective the Joulc -Thotnson effect is important because it can be linked directly to the nature of intermolecular forces between gas molecules [205]. Consider, for example, a classic ideal gas as the simplest case in which molecules do not interact by definition. For this model it is simple to show that as a consequence of the absence of any intermolecular interactions a Joule-Thomson effect does not exist, that is, <5 = 0 [200, 201]. If, on the other hand, the ideal gas is treated quantum mechanically, it can be demonstrated [206] that a Joule-Thomson effect exists (S 0) despite the lack of intermolecular interactions. 

However, the key quantity in the context of the. Joule-Thomson effect is the expansivity defined in Eq. (5.132). From the thermodynamic definition and the statistical phy.sical Eqs. (5.197) and (5.198), it is immediately clear that... 

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