Apparent molar volumes and heat capacities of aqueous acetic acid and sodium acetate at temperatures from T=278.15 K to T=393.15 K at the pressure 0.3(5) MPa

Apparent molar volumes V-phi and heat capacities C-p,C-phi of aqueous solut ions of acetic acid (CH3CO2H) and sodium acetate (CH3CO2Na), and C-p,C-phi for hydrochloric acid (HCl) and sodium hydroxide (NaOH) were determined at temperatures from T = 278.15 K to T = 393.15 K at the pressure 0.3(5) MPa. Apparent molar volumes were obtained from density measurements using an Ant on Paar vibrating-tube densimeter (DMA 512, Anton Paar, Austria). Heat capa cities were obtained using a fixed-cell, power-compensation, differential-o utput, temperature-scanning calorimeter (NanoDSC model 5100, Calorimetry Sc iences Corporation, Prove, UT). Infinite dilution partial molar volumes V-o and heat capacities C-p(o) were obtained over the range of temperatures by extrapolation to m = 0 of the fitted surfaces (Y-phi, T, m). The volume re sults were combined with values of V-o from the literature for aqueous NaCl , HCl, and NaOH to obtain Delta(r)V(m)(o) for ionization of acetic acid, Me asured values of C-p,C-phi were extrapolated to m = 0 for HCl(aq) and NaOH( aq) and used to obtain values of Delta(r)C(p,m)(o) for ionization of CH3CO2 H(aq). The values of Delta(r)V(m)(o) and Delta(r)C(p,m)(o) allow the determ ination by integration of the equilibrium constant K-a and other thermodyna mic properties for ionization of CH3CO2H(aq) from T = 278.15 K to T = 393.1 5 K at the pressure 0.35 MPa. (C) 1999 Academic Press.