Table 1 Experimental heats of formation of barium and sodium molybdates and vanadates from the component oxides AH298, individual values selected value kJ/rnol kJ/molCompound NazO . MOO, -375.0. -365.5, -381.8 -374.1 i 9.0 Na2O . 2 MOO, -449.6, -459.6, -458.4 -455.8 i 6.0 NazO . Vz05 -419.4, -425.4, -410.8 -418.5 i 7.0 2Na20 . V205 -657.0 i 6.0 3 NazO . V205 -886.8, -888.0 -887.4 i 4.0 -65 1.65, -662.2 is strongly exothermic and one component has a moderately low melting point, as exemplified by the calorimeter designed by W. A. Roth for the formation of ferrous sulphide from the elements. A somewhat more sophisticated calorimeter bf this nature has here been constructed to determine the heats of combination of the basic oxides BaO and Na,O with the rather low-melting-point oxydic oxides MOO, and V,O,. The following heats of formation for the molybdates and vanadates from the simple oxides have been obtained: BaO MOO, -224.8 f 3.0 kJ/mol BaO . V,O, -183.8 f 4.0 kJ/mol Na,O. MOO, -374.1 f 9.0 kJ/mol Na,O . 2 MOO, -455.8 f 6.0 kJ/mol Na,O . V,O, -418.5 k 7.0 kJ/mol 2 Na,O . V,O, -657.0 * 6.0 kJ/mol 3 Na,O . V,O, -887.4 f 4.0 kJ/molThe authors are grateful to the 'Deutsche Forschungsgemeinschaft' which supported this work financially and to Mr. Shu-Wu Cheng who carried out some of the measurements.
Apparate und Methoden / Oberfachenerscheinungen / Phasenum wandlungenThe twin cascaded Knudsen cell makes possible improved comparative measurements of effusion processes on sample pairs exhibiting widely differing evaporation temperature ranges. Investigating the polymorph system Arsenolite-Claudetite no significant differences in the evaporation behaviour of both polymorphs can be found.
Einleitungde nur Aussagen innerhalb eines relativ groRen Fehlerbereichs.
