Standard heats of formation of two sodium pyrophosphates, sodium trimetaphosphate, and sodium tetrametaphosphate

Abstract

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.'

Standard enthalpy of formation of disodium hydrogen phosphate hexahydrate and sodium diphosphate

“…As mentioned above, the heat of formation of Na 2 HPO 4 Á6H 2 O has never been previously determined but that of Na 4 P 2 O 7 has been determined by Borisova et al [6] in 1996 (À876.0 ± 4.0 kJ/mol) by using HNO 3 3 mol Á dm À3 as a solvent, Irving and McKerrell [10] in 1968 (À3192.3 ± 4.1 kJ/mol) using a 60% perchloric acid solution and Meadowcroft and Richardson [11] in 1963 (À880.3 ± 10.0 kJ/ mol) using a HCl 6N solution. A considerable divergence is observed but the papers published in 1968 and 1996 reported erroneous values from that of 1963 and 1968, respectively.…”

“…Enthalpy of formation of disodium hydrogen phosphate hexahydrate (Na 2 HPO 4 Á6H 2 O) is unknown, however that of sodium diphosphate was determined by three authors [6,10,11] but one of the published values [10] differs considerably from the other values.…”

Standard Formation Enthalpy of Na2O–ZnO–P2O5 Series Glasses

“…Calculation gives Δ dil H 1 = − 0.017 kJ mol −1 H 3 PO 4 The for mation enthalpy of sodium tr imetaphosphate ((NaPO 3 ) 3 , cr) has been deduced as (− 3762.5 ± 175) kJ mol −1 . This quantity was previously determined by Irving et al [32] in 1968 as − 3672.55 kJ mol −1 by dissolving in a 60% perchloric acid solution [32]. The obtained value differs from the former one by only 2.4%.…”

“…However, access to these quantities involves the formation enthalpy of sodium trimetaphosphate, ((NaPO 3 ) 3 , cr). Because of the very old value reported in literature [32], this quantity has been determined again by the same technique.…”

Enthalpies of formation of vitreous and crystalline pyrophosphates of (lithium oxide or sodium oxide + zinc oxide + phosphorus pentoxide)

“…Phase relationships in {xLi 4 P 2 O 7 + (1 − x)Zn 2 P 2 O 7 } have not been studied. In terms of thermodynamics, there are only some values on the molar enthalpies of formation at ambient temperature of crystalline Na 4 P 2 O 7 , (3)(4)(5) Zn 2 P 2 O 7 , (5) and Li 4 P 2 O 7 .…”