RT Journal Article T1 Thermodynamics of a pure substance at the triple point A1 Velasco Maíllo, Santiago A1 Fernández Pineda, Cristóbal AB A thermodynamic study of a pure substance at the triple point. is presented. In particular, we show that the mass fractions of the phases coexisting at the triple point obey lever rules in the specific entropy-specific volume diagram, and the relative changes in the mass fractions present in each phase along reversible isochoric and adiabatic processes of a pure substance at the triple point are governed by the relative sizes of the segments of the triple-point line in the pressure-specific volume diagram and in the temperature-specific entropy diagram. Applications to the ordinary triple point of water and to the triple point of Al2SiO5 polymorphs are presented. PB American Association of Physics Teachers SN 0002-9505 YR 2007 FD 2007-12 LK https://hdl.handle.net/20.500.14352/50780 UL https://hdl.handle.net/20.500.14352/50780 LA eng NO © 2007 American Association of Physics Teacher. One of the authors (S.V.) acknowledges financial support by the Ministerio de Educación y Ciencia of Spain under Grant Nos. FIS2005-05081 FEDER and FIS2006-03764 FEDER. NO Ministerio de Educación y Ciencia of Spain DS Docta Complutense RD 10 abr 2025