Heat Capacities of Aqueous Solutions of Nitric Acid to High Concentrations and Elevated Temperatures

Volumetric isobaric heat capacities of aqueous solutions of nitric acid have been measured in a modified commercial differential scanning calorimeter fitted with purpose-built tantalum cells over the temperature range of (325.15–473.45) K, at molalities up to 15.0 mol·kg–1, and at 2.0 MPa pressure. These data were combined with recent density measurements to produce apparent molar isobaric heat capacities. The results so obtained were fitted using a Redlich-Rosenfeld-Meyer-type equation, which gave average and maximum deviations of (0.7 and 5) J·K–1·mol–1, respectively. The present results are in good agreement with the literature data available at lower temperatures and concentrations. More importantly, these data represent a major extension of the thermodynamic database for these industrially vital solutions.