Standard enthalpy of formation of lithium diphosphate

• (Li4P2O7) was synthesized from (NH4H2PO4) and (Li2CO3).
• Formation enthalpy of (Li4P2O7) was deduced considering two hypothetical cycles.
• Dissolution and mixing processes were carried out in a C80 SETARAM calorimeter.
• The values deduced for ΔfH° of (Li4P2O7) are (−3147 and −3383.4) kJ/mol−1.
• −3383.4 kJ/mol−1 is in better agreement with most of literature data.

Lithium carbonate (Li2CO3) and ammonium dihydrogen phosphate (NH4H2PO4) were used for synthesizing lithium diphosphate (Li4P2O7). The purity of the latter compound was checked up by X-ray diffraction. The heat of dissolution of (Li4P2O7) in phosphoric acid solution was measured in a C-80 SETARAM calorimeter. Many dilution and mixing processes in acid solutions of several concentrations (w/w) H3PO4, were also realized in the calorimeter in order to get the standard enthalpy of formation of this product. Two thermochemical cycles were investigated and the obtained values for the enthalpy of formation are: (−3383.4 and −3147) kJ · mol−1. The former one is in better agreement with literature data.