The Gibbs phase rule: an experimental path for its recognition and application

This paper proposes a conceptual path about a theme which lies at the border between physics and chemistry, which, though usually neglected, is nowadays very important in materials science: the Gibbs phase rule. It is illustrated by means of significant measurements aimed at clarifying the concepts involved (i.e. phase and degree of freedom), at extracting the phase rule itself on a phenomenological basis, and applying it as an interpretative tool. The main steps suggested for an educational path are the following: elementary experiments and discussion for a glossary, measurements of the temperature as a function of heating or cooling time for mixtures with different compositions, experimental data observation in graphical form to recognize the indicators of the phase transitions which occur, compilation of tables of the quantities involved in the phase rule, and discussion and identification of the phase sequence during the processes.