Thermodynamics of aqueous acetic and propionic acids and their anions over a wide range of temperatures and pressures

Abstract

The apparent molar volumes of aqueous acetic acid were determined ia density measurements at 298 K<T<573 K and 10 MPa<p<38 MPa. The results were corrected for acid ionization and extrapolated to the standard state of infinite dilution. The new data have been combined with literature values of the standard molar volumes and standard molar heat capacities of acetic and propionic acids, and of acetate and propionate ions. Three correlation models were tested in the description of the standard thermodynamic properties at superambient conditions for the two acids and their anions. The most dependable model, inspired by the fluctuation solution theory, has been selected for generation of the recommended data. Adjustable parameters of the model were obtained by simultaneous correlation of the volumes and heat capacities together with experimental dissociation constants of the acid. It is shown that this model can be used for precise and consistent calculations of standard thermodynamic properties of the two acids and their conjugate ions over a wide range of temperatures and pressures.