Thermodynamics of liquid mixtures : experimental and theoretical studies on the thermochemical and volumetric behaviour of some liquids and liquid mixtures.
Govender, Ursula Penelope.
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The excess molar volumes VEm and the excess molar enthalpies HEm have been determined for several binary systems at 298.15 K using an Anton Paar Digital Densitometer and a 2277 Thermal Activity Monitor, respectively. VEm and HEm have been determined over the whole composition range for three types of binary mixtures involving hydrogen bonded interactions. The three types are: (i) a short chain alkanol (methanol, ethanol, 1-propanol, 2-propanol) or (ii) a symmetrical secondary amine (di-n-ethylamine, di-n-propylamine) or (iii) 1-alkyne (l-hexyne, 1-heptyne, l-octyne) with a branched chain ether (diisopropyl ether, 1,1-dimethylethyl methyl ether, 1,1dimethylpropyl methyl ether) and a cyclic ether (tetrahydrofuran, tetrahydropyran, 1,4dioxane). For mixtures of (an alkanol + a branched chain ether or a cyclic ether) the results are explained in terms of the strong self association exhibited by the alkanol and the cross association of the OH:::::O specific interaction. In particular for mixtures of (an alkanol + a cyclic ether) the results show trends relating to the size of the cycloether ring and the number of carbon atoms in the alkanol molecule. For mixtures of a secondary amine + a branched chain ether or a cyclic ether the experimental results have been explained on the basis of the strong molecular interactions (NH·····O) between the weakly self associating secondary amine and the ether oxygen. For binary mixtures of 1-alkyne + a branched chain ether the results indicate a dominance of the π....π interaction over either the dissociation effects of the 1-alkyne (π..... π interactions) or the breakdown of the branched chain ether molecules self association. Thermophysical property data, density p, cubic expansion coefficient ex and isothermal compressibility KT have also been determined for several aliphatic ethers from 288.15 K to 328.15 K at pressures ranging from 0.1 to 8 MPa. The molar volumes derived from the densities have been fitted to a polynomial as a function of temperature and pressure and the second order thermodynamic functions, the cubic expansion coefficient ex and the isothermal compressibility KT determined. For all the ethers, the cubic expansion coefficients decrease with an increase in temperature or pressure while the isothermal compressibilities increase with an increase in temperature or pressure over the temperature and pressure ranges investigated. This work was carried out in the Thermodynamics laboratory of the Indian Institute of Technology in India. This data was required so that the experimental VEm and HEm data could be analyzed using modern theories of liquid mixtures. The VEm and HEm data presented here has been subjected to the following theoretical analysis: (i)The Extended Real Associated Solution (ERAS) model, (ii)The Modified Universal Functional Activity Coefficient (UNIFAC) group contribution model and (iii) The simple Flory and the Prigogine Flory Patterson theory (PFP). All the theories exhibited partial success when applied to the systems investigated here. Excess molar volumes and excess molar enthalpies, VEm and HEm have also been determined over the whole composition range for binary mixtures involving symmetrical (a straight chain ether or ketone + a pseudo straight chain ether or a pseudo straight chain ketone) to test the applicability of the congruency theory. Not all of the mixtures satisfied the null test of the congruency principle.
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