Standard Molar Formation Enthalpy of NH4Fe(HPO4)2

Ammonium-iron(III) bis(hydrogenphosphate) was synthesized via solid-state reaction at low temperature and characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscope. Standard molar enthalpy of formation was determined by an isoperibol solution calorimeter at 298.15K. The results show that the obtained product is NH4Fe(HPO4)2 with shape of Lamellar particles. According to Hess's law, a new thermochemical cycle was designed, and the standard enthalpy of formation of the titled complex at 298.15K is: ΔfHmφ[(NH4)Fe(HPO4)2 (s), 298.15K] = −2641.52 ±0.06 kJ·mol−1.