(58e) Teaching and Learning Gibbs Free Energy and the Phase Equilibrium Criteria through 3D Phase Diagrams for Pure Components

This work is related to a previous one regarding the representation of Thermodynamic Properties in 3D diagrams. This time it is focused on the analysis of Free Gibbs Energy for pure components to achieve a better understanding of the equilibrium criteria of fluid phases.

The fundamental property relations are obtained from the substitution of the first and second Law of Thermodynamics to define the thermodynamic equilibrium state of a closed system, thus the independent variables are not chosen arbitrarily.

The thermodynamic properties data for water are plotted in 3D to represent the resulting equations for G (Gibbs free energy). The database was taken from Haar et. al. (1984) and introduced in Matlab®. Different colors were used to distinguish the various regions: homogeneous liquid phase, homogeneous gas phase, vapor-liquid region and supercritical fluid. The mesh is constructed with values at constant temperature and pressure and the curves for constant vapor fraction are included inside the vapor-liquid region.

The 3D diagrams obtained can be used to generate projections in 2 dimensions: P-G, G-P, T-G, G-T for fluid homogeneous phases and vapor-liquid equilibrium. The behavior of free Gibbs energy may be associated to other concepts like fugacity and fugacity coefficient to be used as additional equilibrium criteria.

It is evident the complexity that engineering students have to handle when the professor starts the study of thermodynamic properties, but a deeper understanding could be attained by adding a visual approach. In the last few years, this methodology has been applied in the Thermodynamics course for sophomore Chemical Engineering students. The professor has perceived that both, students and teachers, show good acceptance of this educational material and the evaluations have revealed a better understanding of these concepts.

The success of this approach relies on the proven fact that the learning experience is more effective when more senses are involved.