Enthalpy of formation of natural hydrous copper sulfate: Chalcanthite

•The enthalpy of dehydration of chalcanthite were measured using Tian–Calvet microcalorimeter.•The values of ΔfHm0 (T = 298.15 K) of natural chalcanthite and synthetic hydrous copper sulfate (blue vitriol) were determined by melt solution calorimetry.

This paper presents the results of the thermochemical study of hydrous copper sulfate CuSO4·5H2O performed on a high-temperature heat-flux Tian–Calvet microcalorimeter. The samples of two natural chalcanthite (Kosmurun ore deposit, Kazakhstan, and Lavrion deposit, Greece) and synthetic hydrous copper sulfate (blue vitriol) were characterized by X-ray microprobe analysis, X-ray powder diffraction, thermal analysis, FTIR and Raman spectroscopy. The enthalpy of dehydration at T = 298.15 K was measured, and the standard molar enthalpies of formation from the elements were determined by the melt solution calorimetry in accordance with Hess’s law. The values of ΔfHm0 (T = 298.15 K) were found to be −(2267.2 ± 4.1) kJ⋅mol−1 for natural chalcanthite and −(2272.6 ± 6.0) kJ·mol−1 for synthetic hydrous copper sulfate (blue vitriol).