Thermodynamics of Compounds Based on Lead(II) and Zinc(II) Oxides in Gas Phase

Abstract

The Knudsen effusion method with mass-spectral analysis of the gas phase has been used to study the vaporization processes in the PbO–ZnO system in the temperature range of 1010–1120 K. It has been found that the saturated vapor above the system consists of lead monooxide molecules, its associates, lead atoms, oxygen molecules, and mixed oxides PbZnO2, Pb2ZnO3, PbZn2O3, Pb2Zn2O4, and Pb3ZnO4. The molar composition of the saturated vapor has been determined and the partial pressures of all components of the gas phase have been obtained at 1110 K. The experimental data made it possible to calculate a number of standard enthalpies of heterophase reactions and standard enthalpies of formation of mixed oxides using the second law of thermodynamics: $${{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }$$ (PbZnO2) = –290.4 ± 6.6 kJ/mol, $${{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }$$ (Pb2ZnO3) = –488.2 ± 21.5 kJ/mol, $${{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }$$ (PbZn2O3) = –628.4 ± 11.9 kJ/mol, $${{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }$$ (Pb2Zn2O4) = –883.2 ± 15.1 kJ/mol, and $${{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }$$ (Pb3ZnO4) = –697.1 ± 31.6 kJ/mol.