GROUP ADDITIVITY EQUATIONS OF STATE FOR CALCULATING THE STANDARD MOLAL THERMODYNAMIC PROPERTIES OF AQUEOUS ORGANIC SPECIES AT ELEVATED TEMPERATURES AND PRESSURES

Abstract

Group additivity equations of state for aqueous organic molecules have been generated by combining the revised Helgeson-Kirkham-Howers (HKF) equations of state with experimental values of the standard molal properties of aqueous alkanes, alkanols, alkylbenzenes, carboxylic acids, amides, and amines. Equations of state parameters for the groups represented by -CH2-, -CH3, -CHCH3, -C6H5, -CH2OH, -COOH, -CONH2, and -CH2NH2 were determined by regression of the experimental data. This procedure permits calculation of the standard molal thermodynamic properties of these groups at elevated temperatures and pressures. Although curves representing the apparent standard molal Gibbs free energies (∆G°) and enthalpies (∆H°) of formation, and the standard molal entropies (S°) of the groups as a function of temperature and pressure are respectively similar for each of them, the temperature dependence of the standard molal heat capacities (C°P) and volumes (V°) of a number of the groups are quite different from one another. For example, the standard molal heat capacities of the hydrocarbon groups minimize with increasing temperature, but those of -CH2OH and -CH2NH2 maximize. Computed values of ∆G° ∆H°, S°, C°P, V°, and the equations of state parameters for the various groups were used together with group additivity relations to generate corresponding values of these properties for aqueous n-alkanes, 2-methylalkanes, n-alkylbenzenes, n-alkanols, n-carboxylic acids, n-amides, and n-amines at temperatures {le} 250°C and pressures {le} 1 kbar.