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In adiabatic vacuum and dynamic calorimeters, the temperature dependence of the standard molar heat capacity C p , m o of 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 C p , m o / R , Δ 0 T H m o ( R · K ), Δ 0 T S m o / R , and Φ m o = Δ T 0 S m o − Δ T 0 H m o / T ( where R is the universal gas constant) in the range T → 0 to T = 450 K, and the standard thermochemical parameters of formation Δ f S m o , Δ f G m o , and lg K f of the cyclophosphazenes from the elements at T = 298.15 K. The isochoric heat capacities C V , m of both chlorocyclophosphazenes have been estimated over the range T → 0 to T fus . The first and the second cryoscopic constants have been determined. The difference in the thermodynamic properties for one phosphazene group (–NPCl 2 –) has been explained in terms of the different compositions and structure of the rings. |
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