General formulae based on the theory of association equilibria. Heat capacity, compressibility and expansion of associated systems

Abstract

Using the principle of association equilibrium, two equations have been derived for the contribution of association to heat capacity in an athermal associated system. Both equations are equivalent and hold for any reasonable pattern of equilibrium association species if association does not give rise to an infinite three-dimensional structure. In the first equation the association heat capacity is expressed by means of statistical moments of association equilibrium; in the second the same quantity is described by using energy changes accompanying restructuralization processes between the association species. Examples are given which demonstrate that by specifying one of the two relations derived in this study, it is possible to obtain quickly equations for C_p of the given model. The theory can be extended to include isothermal compressibility and heat expansion of associating systems.