SIGNIFICANCE OF THE WILSON CONSTANTS IN THE THEORETICAL DESCRIPTION OF VAPOR-PRESSURES OVER BINARY-MIXTURES

The significance of the Wilson constants in the approximate mathematical description of the vapour pressures over binary mixtures of a self-associating component and an inert solvent is investigated. This is performed by calculating the sum φ{symbol} of the squares of the differences between the measured and the calculated pressures as a function of the two constants and by plotting lines of equal φ{symbol} around the minimum of φ{symbol}. A pair of well-defined Wilson constants is obtained only for systems with strong positive deviation from the straight-line behavior. At smaller deviations a whole range of such pairs describes equally well the vapor pressures; in extreme cases it appears that a single value, like the sum or a linear combination of the two constants, suffices to describe the vapor-pressure function. The interaction energy values inferred from these constants are rather uncertain. © 1979.