THERMODYNAMICS OF THE SYSTEM KRYPTON NITRIC OXIDE AND THEIR INTERPRETATION IN TERMS OF MONOMER-DIMER ASSOCIATION OF THE OXIDE

Calado, J.C.G. and Staveley, L.A.K., 1979. The thermodynamics of the system krypton-nitric oxide and their interpretation in terms of monomer-dimer association of the oxide. Fluid Phase Equilibria, 3: 153-166. Measurements hav ebeen made of the total vapour pressure of KrNO mixtures at 115.76 K, from which the excess Gibbs energy GE has been calculated. The excess molar volume VE has also been measured at the same temperature. The system has a positive azeotrope, and VE is throughout positive and a somewhat asymmetric function of composition. An attempt has been made at a quantitative interpretation of the pressure results on the basis of equilibrium between nitric oxide monomers and dimers, with the value of the equilibrium constant given by a previous magnetic susceptibility study. We have assumed that there is an ideal relationship between monomers and dimers in a solution, but not between these species on the one hand and krypton molecules on the other. We find that, assuming the experimental value of the total vapour pressure at the highest and lowest krypton concentration studied, the total vapour pressure at the remaining concentrations can be calculated to better than one per cent. Roughly, 60 per cent of the observed non-ideality for the equimolar mixture appears to be due to the monomer-dimer association, and the remainder to the interaction between the two forms of nitric oxide and the krypton molecules,. © 1979.