Collect. Czech. Chem. Commun. 1997, 62, 679-695

Extremes in Dependences of Enthalpy and Entropy of Saturated Vapour on Temperature

Josef P. Nováka, Anatol Malijevskýa, Jaroslav Dědekb and Jiří Oldřichc

a Department of Physical Chemistry, Prague Institute of Chemical Technology, 166 28 Prague 6, Czech Republic
b Plynoprojekt Praha, 120 00 Prague 2, Czech Republic
c CKD Kompresory a.s., 190 02 Prague 9, Czech Republic


It was proved that the enthalpy of saturated vapour as a function of temperature has a maximum for all substances. The dependence of the entropy of saturated vapour on temperature can be monotonous, has a minimum and a maximum, or has only a maximum. The thermodynamic relations were derived for the existence of the extremes which enable their computation from the knowledge of dependence of the ideal-gas heat capacity on temperature and an equation of state. A method based on the theorem of corresponding states was proposed for estimating the extremes, and its results were compared with literature data. The agreement between the literature and estimated temperatures corresponding to the extremes is very good. The procedure proposed can serve for giving precision to the H-p and T-S diagrams commonly used in applied thermodynamics.

Keywords: Enthalpy; Entropy; Saturated vapour.