Vapor-liquid equilibrium data is obtained using the following relationship for this ideal system:

, where

This Demonstration shows the density plot of the function for user-set values of the relative volatility. For regions near any pure component, the calculated function is close to zero. These regions are shown in blue. On the other hand, in orange regions the liquid-phase composition is very different from its vapor-phase counterpart and the function values are quite large. You can select a case in which the relative volatility of components and is close to unity, for example, and observe that the region near the side (i.e. for very small mole fraction of component ) is blue since we have almost a binary mixture and the volatility of the components and are the same: there is practically no difference in the vapor-phase and liquid-phase compositions, as you can see in the last snapshot.