Fluorine-combustion calorimetric determinations of the standard molar enthalpy changes for the formation of SiSe2(cr), SiSe1.94(cr), and SiSe1.94(vit), and for the transition: SiSe1.94(vit) = SiSe1.94(cr) at the temperature T = 298.15 K. Implications of the results for the enthalpies of dissociation Dom(Se—SiSe) and Dom(SiSe). Thermodynamic properties of SiSe(g)

Abstract Fluorine-bomb calorimetry was used to determine the standard massic energies of combustion Δ c u o of the silicon selenides SiSe 2 (cr), SiSe 1.94 (cr), and SiSe 1.94 (vit), according to the combustion reaction: SiSe v (s) + (2 + 3 v )F 2 (g) = SiF 4 (g) + v SeF 6 (g). The following additional results were derived for the standard molar energy of combustion Δ c U o m ; the standard molar enthalpy of combustion Δ c H o m ; and the standard molar enthalpy of formation Δ f H o m , all at the temperature T = 298.15 K and for the standard pressure p o = 101.325 kPa See Table. Standard thermodynamic properties of the gas SiSe(g) were calculated by means of the conventional formulae of statistical mechanics. On the basis of the thermochemical quantities given above, the standard molar enthalpy of the transition: SiSe 1.94 (vit) = SiSe 1.94 (cr) is Δ trs H o m = -(6.5 ± 2.2) kJ·mol -1 at T = 291.15 K. (All uncertainties in this abstract correspond to twice the standard deviation of the mean.) Implications of the thermochemical quantities for the enthalpies of dissociation D o m (SiX) and D o m (X-SiX), where X denotes O, S, or Te.