Apparent molar volumes V-phi and heat capacities C-p,C-phi of aqueous solutions 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 Anton Paar vibrating-tube densimeter (DMA 512, Anton Paar, Austria). Heat capacities were obtained using a fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC model 5100, Calorimetry Sciences 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 results 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, Measured 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 CH3CO2H(aq). The values of Delta(r)V(m)(o) and Delta(r)C(p,m)(o) allow the determination by integration of the equilibrium constant K-a and other thermodynamic properties for ionization of CH3CO2H(aq) from T = 278.15 K to T = 393.15 K at the pressure 0.35 MPa.