Thermodynamic and thermochemical properties of Cu3(PO4)2·3H2O

Abstract

Copper (II) orthophosphate trihydrate Cu3(PO4)2·3H2O has been synthesized by the exchange chemical reactions in aqueous solutions from the compounds Cu(NO3)2·3H2O, NH4OH and H3PO4. The final product has been investigated by using atomic absorption spectroscopy (AAS), infrared spectrometry (IRS), differential thermal analysis (DTA) and X-ray powder diffraction (XRD) techniques. For the first time, the experimental heat capacity Ср° of Cu3(PO4)2·3H2O has been investigated in the temperature range 198‒402 K. Combining the experimental results with the literature data made it possible to determine the thermodynamic and thermochemical properties, such as enthalpy НТ° , entropy SТ° , Gibbs energy GТ° , enthalpy of formation ΔHf°(T), Gibbs energy of formation ΔGf°(T) and logarithm of the equilibrium constant of formation reaction log[Kf°(T)], for the title compound. It was found that at the extreme temperatures of the experiment, Cu3(PO4)2·3H2O has Ср° = 245.96 J·mol–1·K–1, Н° = –3169.59 kJ·mol–1, S° = 311.34 J·mol–1·K–1, G° = –3231.24 kJ·mol–1 (at 198 K); Ср° = 455.31 J·mol–1·K–1, Н° = –3097.93 kJ·mol–1, S° = 551.48 J·mol–1·K–1, G° = –3319.62 kJ·mol–1, ΔHf° = –3138.48 kJ·mol–1, ΔGf° = –2625.39 kJ·mol–1, log[K ] = 341.13 (at 402 K).