The Heat Capacities of Lithium, Sodium, Potassium, Rubidium, and Caesium Nitrates in the Solid and Liquid States

Abstract The heat capacities, Cp, of the alkali metal nitrates, MNO3 (M= Li, Na, K, Rb, and Cs), in the solid and liquid states have been measured between 50 and 450 °C by means of adiabatic calorimetry. We have measured with a fair degree of accuracy the Cp values for the MNO3 systems, because the existing data on NaNO3 and KNO3 above 250 °C are quite scanty. Some empirical rules, some of which may extend to other salts, have been obtained from the results on Cp for the five alkali nitrates in the solid and liquid states. For the molten MNO3, the heat capacities at a constant volume, CV, were obtained from the thermodynamical relationship between CV and Cp, using the experimental values of Cp; the CV values have been interpreted in terms of the interionic and intraionic portions.