Fundamentals of Chemical Engineering Thermodynamics

Chapter 8. Phase Behavior of Mixtures

The presence of multiple components adds a new dimension to the phase behavior of mixtures. In the pure component, molecules are always surrounded by similar species; in a mixture, they are surrounded by both like and unlike species. This gives rise to self-interactions between like molecules, and cross-interaction between unlike molecules. These interactions are much more pronounced in the liquid phase, where molecules are closely packed together. The balance of self- and cross-interactions creates phase behavior that is not seen in pure fluids. If cross-interactions are favorable, components form strong mixtures that are more difficult to separate. If cross interactions are unfavorable, the mixture is weaker ...