The standard heats of formation of Na2H2P20,, Na4P20,, (NaP03)3 and (NaPO& have been AH~NazHzPzO,(c) = -664-7 rfr: 1 .O kcal/mole-l; AH; Na4P207(c) = -763.7f1.0 kcal/mole-l; AH; (NaPO&(c) = -878.6k1-5 kcal mole-'; AH; (NaPO&c) = -1169.4320 kcal mole-'.determined by solution calorimetry. The values obtained at 298°K are :In previous papers we have reported the standard heats of formation of H3P04 0.6416 H20, NaH,PO,, Na2HP04 and Na3P04. In this present study we use some of that data in conjunction with further experimental results to obtain heats of formation of Na2H2P20,, Na4P20,, (NaP03)3 and (NaPO,),.
EXPERIMENTALThe isothermally-jacketed calorimeter and techniques for operating and calibrating it have been described before.'
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