ON THE RELATIONSHIP BETWEEN THE EQUILIBRIUM-CONSTANTS OF CONSECUTIVE ASSOCIATION REACTIONS

Generalized association models for fluids require a large number of adjustable parameters (equilibrium constants) unless some effort is made to interrelate the different association constants. An association model has been developed by considering the probability of consecutive association reactions and the effect of that probability on the entropy of association. The relationship between the equilibrium constants of these reactions has been expressed by a function related to the Poisson distribution. When combined with an equation of state, the model accurately represents the properties of hydrogen fluoride and its mixtures with halogenated hydrocarbons. The Poisson distribution model is compared with the classical continuous linear association model. While the Poisson distribution model is superior for molecules that preferentially form associates of moderate size, the continuous linear model is more appropriate for molecules that can form polymers with a high degree of polymerization.