On the concept of excluded volume for weakly associating gas

This paper aims at further elucidation of the correspondence between the excluded volume, the equilibrium constant and the second virial coefficient (SVC) taking a simple classical system as an example. It is shown that the use of partitioning of pair states in the phase space makes it possible to rigorously define temperature variations of excluded volume in terms of the so-called ‘free’ component of the SVC obtained by statistical averaging over unbound pairs.