Thermodynamic properties of organic compounds

Abstract

By employing calorimetric and cryometric methods, the melting total and the premelting enthalpies of stearic acid were measured and the phase diagrams of the solidliquid equilibria stearic acid + A (where A is an aromatic compound or a dicarboxylic acid or I~) were determined.In this paper the results of calorimetric and cryometric studies on stearic acid are reported. ExperimentalThe calorimetric measurements were performed with a Perkin-Elmer Differential Scanning Calorimeter (DSC-IB). The details of the calibration were given in previous papers [1,2]. The description of the cryometric measurements method is reported in the notes [3,4]; the crystallization temperatures of the melts were Fig. 1. Cell for the cryometric measurements of volatile substances 7

Dependence of the viscosities of some organic aliphatic acids on temperature and molar volume

“…ofC-R which, as demonstrated \OH... in preceding papers [1,2] is the structural entity of the fusion. The length [6] 12 is calculated in the following way: where N is Avogadro's number and 7 represents the number of cylinders contained in each hexagonal prism.…”

“…The fusion entropies of these acids [1,2] are a linear function of the parameter (b -Vp,r,l. ), i.e.…”

“…The dependence of the viscosity on the molar volume permitted calculation of the covolume, which is compared to that obtained from structural data.The thermodynamic properties of fusion of organic aliphatic acids from C10 to Cas were dealt with in two preceding notes [1,2], in which two stages were distinguished in the fusion process: prefusion and actual fusion. The prefusion enthalpy for stearic acid represents a value of about 10 70 of the fusion enthalpy; this value decreases from stearic acid to the acids with lower molecular weights.…”

The covolumes of the fused aliphatic acids from C9 to C18 and of C2, from viscosity measurements

“…In Fig. 2 Acetic acid, ordinate from 0.04 to 0.12 at the melting point begins to rotate around the a axis, the melting entropy [3,4] should be an univocal function of the moment of inertia I = 2; mr ~ of the dimer about the axis. This fact, that all values (reported in [3,4]) of AS lie on a smooth line, is demonstrated in Fig.…”

“…2 Acetic acid, ordinate from 0.04 to 0.12 at the melting point begins to rotate around the a axis, the melting entropy [3,4] should be an univocal function of the moment of inertia I = 2; mr ~ of the dimer about the axis. This fact, that all values (reported in [3,4]) of AS lie on a smooth line, is demonstrated in Fig. 3; the typical alternance of the graph AS versus nc disappears or is very attenuated in the graph AS versus L As regards acetic acid, the results are a little different; in fact b v > Vcy 1.…”