Low Densities The Virial Equation

We know that as the density p approaches zero at a constant temperature T, the product (PV) remains finite and becomes equal to NkT at the limit p = 0, i.e. z = 1, at p = 0. 

A Maclaurin s series expansion in density around p = 0 yields  

In Chapter 8 we used B for the second virial coefficient, C for the third, and so on. Here we use, for generality, 82,8, etc. 8 is the unity that appears before the summation. 

We also stated that the virial coefficients of pure compounds are functions of temperature only. This is apparent here, because they are defined at the limit p = 0, at a specified temperature. 

The virial equation was first proposed by Kammerlingh Onnes in 1901 on a purely empirical basis he also suggested the name void. 

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