Analysis and Thermochemistry of the Equilibrium Vapour of the Nal‐SnI2 and ScI3‐SnI2 Systems

Abstract

AbstractThe NaI‐SnI2 and ScI3‐SnI2 systems were investigated under equilibrium conditions in the temperature ranges between 620 K to 840 K and 726 K to 873 K, respectively, by using a mass spectrometer coupled with a two compartment Knudsen cell. The gaseous species NaI, (NaI)2, SnI2, NaSnI3 (NaI‐SnI2 system) as well as ScI3, (ScI3)2, SnI2, ScSnI5 (ScI3‐SnI2 system) are present in the vapours. Their partial pressures were employed in a second‐law evaluation. The enthalpy and entropy changes of the dissociation reactionsNaSnI3(g) ⇌ NaI(g) + SnI2(g) (1)andScSnI5(g) ⇌ ScI3(g) + SnI2(g) (2)as well as of the reactions for the vapour transport of Na or ScNaI(s) + SnI2(g) ⇌ NaSnI3(g) (3)andScI3(s) + SnI2(g) ⇌ ScSnI5(g) (4)resulted as ΔdH0298 (Eq. (1)) = 166 ± 5 kJ mol−1, ΔdS0298 (Eq. (1)) = 144 ± 7 J mol−1 K−1; ΔdH0298 (Eq. (2)) = 172 ± 8 kJ mol−1, ΔdS0298 (Eq. (2)) = 181 ± 11 J mol−1 K−1; ΔrH0298 (Eq. (3)) = 25 ± 3 kJ mol−1, ΔrS0298 (Eq. 3)) = −1.3 ± 4 J mol−1 K−1; and ΔrH0298 (Eq. (4)) = 94 ± 6 kJ mol−1, ΔrS0298 (Eq. (4)) = 47 ± 7 J mol−1 K−1. The equilibrium constants for these reactions are also given. The data are discussed with respect to their significance for chemical vapour transport and for semi empirical rules used to predict the dissociation enthalpies of gaseous heterocomplexes.