The heat capacity and thermodynamic functions of pyromorphite over the temperature range 5–320 K

Abstract

The heat capacity of natural mineral, pyromorphite Pb5(PO4)3Cl, was measured over the temperature range 4.2–320 K using low-temperature adiabatic calorimetry. An anomalous temperature dependence of heat capacity with a maximum at 273.24 K was observed between 250 and 290 K. The heat capacity, entropy, enthalpy, and reduced thermodynamic potential of pyromorphite were calculated and tabulated over the temperature range 5–320 K. The standard thermodynamic functions of the mineral are Cp298.15o = 414.98 ± 0.44 J/(mol K), S298.15o = 585.31 ± 0.99 J/(mol K), H298.15o − H0o = 80.90 ± 0.08 kJ/mol, and Φ298.15o = 313.97 ± 0.84 J/(mol K).