Thermodynamics of hexachlorocyclotriphosphazene and octachlorocyclotetraphosphazene fromT → 0 toT = 450 K

Abstract

In adiabatic vacuum and dynamic calorimeters, the temperature dependence of the standard molar heat capacity Cp , moof hexachlorocyclotriphospazene and octachlorocyclotetraphosphazene has been determined at temperatures in the range T= 5 K to T= 450 K: from T= 5 K to T= 340 K with an accuracy of about 0.2 per cent, and with an accuracy of 0.5 to 1.5 per cent between T= 340 K and T= 450 K. The temperatures, enthalpies, and entropies of melting of the above compounds have been determined. The experimental data were used to calculate the thermodynamic functions Cp , mo/R , Δ0THmo(R·K), Δ0TSmo/R , and Φmo=ΔT 0 Smo−ΔT 0 Hmo/T( where R is the universal gas constant) in the range T→ 0 to T= 450 K, and the standard thermochemical parameters of formation ΔfSmo, ΔfGmo, and lg Kfof the cyclophosphazenes from the elements at T= 298.15 K. The isochoric heat capacities CV , mof both chlorocyclophosphazenes have been estimated over the range T→ 0 to Tfus. The first and the second cryoscopic constants have been determined. The difference in the thermodynamic properties for one phosphazene group (–NPCl2–) has been explained in terms of the different compositions and structure of the rings.