Thermochemistry of formation of sodium polyphosphates from sodium orthophosphates

Abstract

The heats of formation of crystalline Na₂H₂P₂O₇, Na₄P₂O₇, (NaPO₃)_x, and Na₅P₃O₁₀ from crystalline sodium orthophosphates were measured using a differential scanning calorimeter. Heats of reaction at 298 K were calculated from the heat capacities of the phosphates which were measured from 310–620 K. Results confirm recent values for the heats of formation of NaH₂PO₄, Na₂HPO₄, Na₂H₂P₂O₇, Na₃P₃O₉, and Na₅P₃O₁₀.