Standard Molar Formation Enthalpy of NH₄Fe(HPO₄)₂

Abstract

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: Δ_fH_m^φ[(NH₄)Fe(HPO₄)₂ (s), 298.15K] = −2641.52 ±0.06 kJ·mol⁻¹.

Keywords:

• Ammonium-iron(III) bis(hydrogenphosphate)
• standard molar enthalpy of formation
• solid-state reaction at low temperature
• thermodynamic properties