Standard molar enthalpy of formation of rubidium diphosphate

Rubidium carbonate (Rb₂CO₃) and ammonium dihydrogen phosphate (NH₄H₂PO₄) were used for synthesizing rubidium diphosphate (Rb₄P₂O₇). The purity of the latter compound was checked up by X-ray diffraction. Rb₄P₂O₇ was involved in an hypothetical reaction and dissolved together with the other components in a 3.85 % (m/m) phosphoric acid solution, using a C-80 SETARAM calorimeter. Mixing processes were also realized in the calorimeter in order to get the standard molar enthalpy of formation of rubidium diphosphate (Rb₄P₂O₇). For that a thermochemical cycle was investigated and the obtained value for the standard molar enthalpy of formation of rubidium diphosphate is (?3,183.7) kJ mol^?1. The result is about 1.8 % lower than literature value.