Add time:07/30/2019         Source:sciencedirect.com

The congruent vapourization of solid ytterbium (II) selenide of practically stoichiometric composition was studied over the temperature range 1744–2040 K by the Knudsen effusion weight loss technique. Using enthalpy and entropy data for the gaseous species YbSe, Yb, Se and Se2 as well as estimated data for solid YbSe it could be concluded from a thermodynamic evaluation of the effusion results that ytterbium and selenium are the principal vapour species in equilibrium with the solid compound and that p(YbSe) and p(Se2) are ⪡ p(Yb). The vapourization to the monatomic elements follows logK = (− 42283 ± 417)T−1 + 12.744 ± 0.222 from which the following standard enthalpy was derived by the second (index II) and third (index III) law methods: ΔH298o(II) = 831.4 ± 32.2 kJ mol−1ΔH298o(III) = 833.1 ± 26 kJ mol−1 A value of ΔfH298o [YbSe(s)] = − 444 ± 32 kJ mol−1 was calculated by considering the respective data for Yb(g) and Se(g). This value is critically compared with formation data reported in the literature, and the thermochemical characteristics of YbSe as a member of a series of baride compounds are discussed.

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