Thermodynamic properties of CSI. II. vapour pressures and thermochemical properties of CsI(g) and Cs 2I 2(g)

Abstract

The vapour pressure of caesium iodide has been measured in the vicinity of the melting point (903.5 K). Below the melting point dimerization in the vapour is negligible. The vapour pressure can be expressed as: log p/atm = (−9550 ± 79)/ T + (6.945±0.093) and for the enthalpy of sublimation, according to the “third law method”, the value Δ H 0 298.15 = 193.1 ± 0.1 kJ mol −1 has been found. Above the melting point a sudden increase in the fraction of dimers has been observed until a value (18.6 ± 1.8)% was reached at ~ 912 K. The vapour pressure of Cs 2I 2(g) can be expressed as log p/atm = (− 7587 ± 530)/ T + (4.19 ± 0.54) and for its enthalpy of sublimation the value Δ H 0 298.15 = 229.9 ± 1.0 kJ mol −1 has been found. From the enthalpies of sublimation it has been found that Δ f H 0(CsI, g, 298.15 K) = −155.0 ± 0.2 kJ mol −1 Δ f H 0(Cs 2I 2,g,298.15K) = −466.4 ± 1.1 kJ mol −1 A discussion of the literature is given.