Vapor pressures and interaction constants of some nearly ideal solutions

Abstract

The experimental study of the nonideal behavior of liquid solutions becomes simplified when the experiment is carried out at low-pressure conditions. The departure of the vapor phase from ideal gas behavior is small, and a reliable estimate can be made for this small departure for many systems. As a result, isothermal total vapor-pressure data at a number of compositions suffice for the description of nonideal solution behavior. For this purpose, the data are analyzed in terms of an assumed expression of activity coefficients such as the Wilson equation or one of the Redlich and Kister equations. The adjustable parameters in the equation are determined so as to reproduce the total vapor-pressure data with minimal errors. The procedure has been much used for the study of binary solutions (9). Sampling and analysis of the vapor phase are avoided. Analysis of the liquid can also be avoided by careful gravimetric or volumetric preparation of the solution from pure liquids. The total vapor-pressure method is particularly adapted to the study of nearly ideal solutions. These are made of highly similar components and show small but significant deviations from ideal solution behavior. The deviations are represented by first-order conformal solution equations ( 5 ) . Experimental observations (70) showed that the activity coefficients y in binary nearly ideal solutions follow the simple equation