Virial Terms Links

While linking structure and thermodynamics based on the virial expression is not straightforward, this link can in fact be established using an alternative desciiptiOTi based on Kirkwood-Buff (KB) theory [76], Whereas the virial route requires information on the effective potential, the KB description does not make any assumption on the nature of the potentials, is exact, and its central quantities can be interpreted in terms of local solution structure. To this end, we consider the derivatives of the salt activity with respect to the density at constant pressure p and temperature T. For the systems shown in Fig. 5 these derivatives show the same order as the osmotic coefficients/salt activities for the different ions [70]. Hence, the microscopic mechanism explaining the order among the derivatives of the salt activity for the different ions also explains the Hofmeister series for the activities obtained by integration of the derivatives. Based on this, the relation between... 

The virial equation of state is especially important since its coefficients can be modeled in terms of nonideality resulting from interactions between molecules. Thus a link is formed between macroscopic gas properties (P,V,T) and the forces between molecules. For a multicomponent mixture, multiple second virial coefficients are needed, one to account for each pairwise interaction. The second virial coefficients for a two-component mixture are Bn, Bn, and B22, where Bn represents the interaction between two molecules of component 1, Bu represents the interaction between a molecule of 1 and a molecule of 2, and B22 represents interaction between two molecules of 2. A tabulation of some compounds whose virial coefficients have been measured by GC is given in Table 12.8. 

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