Thermodynamic origin and graphical methods of phase theory
1 LETIAM, EA7357, IUT Orsay, Université Paris Sud, rue Noetzlin, 91405 Orsay Cedex, France
2 Caractérisation des Matériaux Moléculaires à Activité Thérapeutique - CAMMAT, Faculté de Pharmacie, Université Paris Descartes, 4 avenue de l'observatoire, 75006 Paris, France
a e-mail: email@example.com
Received: 3 October 2016
Published online: 18 April 2017
Thermodynamics is often considered difficult to understand due to extensive use of mathematics. In the present paper, a graphical approach will be used to explain the origin of phase diagrams starting from the fundamental equation of thermodynamics dU = Tds − Pdv defined by J.W. Gibbs. The characteristic variables of this equation are the specific entropy s and the specific volume v, which lead in a straightforward way to s-v phase diagrams. It will be demonstrated through monotonicity of the internal energy curves of the different phases of the system and graphical Legendre transformations how pressure-entropy (P-s) and temperature-volume (T-v) phase diagrams are linked to s-v phase diagrams and how the latter two phase diagrams are related to pressure-temperature (P-T) phase diagrams.
© EDP Sciences, Springer-Verlag, 2017