Direct Determination of Standard Gibbs Energies of the Formation of 4CaO·P<sub>2</sub>O<sub>5</sub> and 3CaO·P<sub>2</sub>O<sub>5</sub> by Transpiration Method
Аннотация:The standard Gibbs energy changes of the following reactions have been measured by using transpiration method; 4CaO∙P2O5(s) + 5C(s) = 4CaO(s) + P2(g) + 5CO(g) ΔGo/kJ = 1624 – 0.953T (± 2.7), (1373 < T/K < 1573) 4(3CaO∙P2O5)(s) + 5C(s) = 3(4CaO∙P2O5)(s) + P2(g) + 5CO(g) ΔGo/kJ = 1946 – 1.193T (± 0.9), (1448 < T/K < 1523) The standard Gibbs energies of the formation of 4CaO∙P2O5 (ΔGof,(4CaO∙P2O5)) and 3CaO∙P2O5 (ΔGof,(3CaO∙P2O5)) have been derived as follows; ΔGof(4CaO∙P2O5)/kJ mol–1 = – 4765 + 0.965 T, (1373 < T/K < 1573) ΔGof(3CaO∙P2O5)/kJ mol–1 = – 4200 + 0.912 T, (1448 < T/K < 1523) The reasons for discrepancies from reported values were discussed from the view point of whether the activity of phosphorus is measured directly or not.
