Solid-Solid-Liquid Phase Diagrams: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key point from this module:
  • When two solid phases that are in equilibrium melt, both solid phases melt, but they melt in proportion to yield the compositon of the liquid phase they are in equilibrium with. They melt at a constant temperature until one of the solid phases has completely melted. Then the temperature increases as more heat is added.
  • The lever rule can only be used when two phases (not three phases) are present.
From studying this module, you should now be able to:
  • Given temperature and mole fraction, use solid-solid-liquid phase diagrams to identify which phases are present.
  • Identify regions where phase changes occur on a phase diagram.
  • Be able to draw and label a solid-solid-liquid phase diagram.


Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder