The apparent molar volumes V-phi and apparent molar heat capacities C-p,C-phi of aqueous solutions of potassium and sodium nitrate and of nitric acid have been determined over the temperature range 278.15 less than or equal to T / K less than or equal to 393.15 and molality range 0.015 less than or equal to m / (mol (.) kg(-1)) less than or equal to 0.5 at the pressure p = 0.35 MPa. Densities of these solutions were measured using a vibrating-tube densimeter (DMA 512, Anton Paar, Austria). The density results were used to calculate V-phi for each solution. The massic heat capacities of these same solutions were measured using a twin fixed-cell, differential-output, temperature scanning calorimeter (NanoDSC model 6100, Calorimetry Sciences Corporation, Spanish Fork, UT, U.S.A.) and these measurements were used to calculate C-p,C-phi for each solute. The V-phi and C-p,(phi) results were fit to semi-empirical equations by regression. These equations were used to calculate the change in volume (m, T, Delta(r) V-m) and the change in heat capacity (m, T, Delta(r)C(p) , m) for ionization of water in KNO3 (aq) and NaNO3 (aq). The (m, T, Delta(r)C(p), m) results were integrated to obtain the change in enthalpy (m, T, Delta(r)H(m)), the molality quotient (m, T, p Q(w)), and change in entropy (m, T, Delta(r)S(m)) for the ionization reaction of water.