Add time:08/09/2019         Source:sciencedirect.com

The vaporization of pure Na2O(c) was investigated at temperatures of 900–1165 K with the method of Knudsen Effusion Mass Spectrometry (KEMS). Thermodynamic quantities of sublimation enthalpy, entropy and Gibbs energy were derived from the partial pressures of gaseous species Na and O2 over the pure sodium oxide reference samples. The sublimation enthalpies obtained for the reaction “Na2O = 2 Na(g) + ½ O2(g)” are for Na: ∆sub H10000 = 243 ± 4, 2nd Law, and 241 ± 3, 3rd law. For O2: ∆sub H10000 = 242 ± 2, 2nd Law, and 241 ± 2, 3rd law kJ mol−1. The Gibbs energy ∆sub G10000 and entropy ∆sub S10000 for sublimation were determined as 133 ± 5 kJ mol−1 and 110 ± 2 J mol−1 K−1 for sodium, and for O2: ∆sub G10000 =143 ± 4 kJ mol−1 and entropy ∆sub S10000 = 100 ± 2 J mol−1 K−1.From the equilibrium constant for the reaction Na2O(c) = 2Na(g) + ½ O2(g) the enthalpy ∆r H10000 resulted in 605 ± 6, 2nd law, and 611 ± 9 kJ mol−1, 3rd law. The Gibbs energy ∆r G10000 and entropy ∆r S10000 were deduced as 342 ± 9 kJ mol−1 and 269 ± 5 J mol−1 K−1.

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