TABLE OF CONTENTS When two liquids are only partially miscible, experimental data for the two mutual solubilities can be used to estimate activity coefficients over the entire range of composition in the homogeneous regions. Suppose the solubility (mole fraction) of component 1 in compound 2 x S ? 2 and that of component 2 in component 1 is x S ? 2 where superscript s E denotes saturation and the primes designate the two liquid phases. If x S ? 1 and x S ? 2 are known at some temperature T, it is possible to estimate activity coefficients for both components in the homogeneous regions 0 ? x S ? 1 ? x S ? 1 and 0 ? x ? 2 ? x S ? 2
To estimate the activity coefficients, it is necessary to choose some thermodynamically consistent analytical expression which relates activity coefficients ? 1 and ? 2 to mole fraction x. (See Sec. 8-5.) Such an expression contains one or more parameters characteristic of the binary system; these parameters are generally temperature-dependent, although the effect of temperature is often not large. From the equations of liquid-liquid equilibrium, it is possible to determine two of these parameters. The equations of equilibrium are
Suppose we choose a two-constant expression for the molar excess Gibbs energy g E. Then, as discussed in Sec. 8-5,
where f
