Gibbs Free Energy Composition and Phase Diagrams of Binary Systems
This chapter examines the qualitative features of common binary equilibrium phase diagrams. It also examines the phase diagrams and discusses some of their important features. The chapter looks at several of the isobaric molar Gibbs free energy versus composition curves that are thermodynamically consistent with the phase diagrams. It shows a simple way that a liquid and solid in a binary isobaric system can be in equilibrium. In the eutectic phase diagrams, the high-temperature liquid phase has a composition between that of the two low-temperature phases at the invariant temperature The Gibbs free energy of mixing expression contains a negative logarithmic term, the magnitude of which is proportional to temperature, and a positive parabolic term which is independent of temperature. With a change in the temperature, the Gibbs energy curves shift relative to one another, since their temperature derivatives are proportional to the entropy of the phases.