Vapor pressure and sublimation enthalpies of holmium trichloride, tribromide, and triiodide

The total vapor pressure of HoCl3, HoBr3, and HoI3 was measured by the torsion and Knudsen effusion methods. By a least-squares treatment of the obtained data, the following equations were selected as representative for the temperature dependence of their vapor pressures in the covered temperature ranges: HoCl3(s), log(p/kPa) ) 10.91 ( 0.10 - (14216 ( 150) (K/T) (from 883 to 994 K); HoCl3(1), log(p/ kPa) ) 9.16 ( 0.10 - (12466 ( 150) (K/T) (from 1002 to 1164 K); HoBr3(s) log(p/kPa) ) 10.95 ( 0.10 - (14168 ( 150) (K/T) (from 904 to 1105 K); HoI3(s), log(p/kPa) ) 12.24 ( 0.10 - (14656 ( 150) (K/T) (from 872 to 1066 K). When the data are treated by the second- and third-law methods, the standard sublimation enthalpies for HoCl3 and HoBr3, DsubH°(298 K) ) 296 ( 10 and 290 ( 5 kJ mol-1, respectively, were derived. For HoI3 the proposed enthalpy, DsubH°(298 K) ) 296 ( 8 kJ mol-1, was only derived by the second-law method. From this standard enthalpy, a set of free energy functions for solid HoI3 was evaluated by a third-law treatment of the data.