Standard sublimation enthalpies of erbium trichloride, tribromide, and triiodide

The total vapor pressures of the erbium trihalides ErCl3, ErBr3, and ErI3 were measured by the torsion method, and their temperature dependences can be expressed by the following equations over the given temperature ranges: ErCl3(s), log(p/kPa) ) 12.04 ( 0.15 - (15159 ( 200)(K/T) from (880 to 1040) K; ErBr3(s), log(p/kPa) ) 11.09 ( 0.15 - (14256 ( 200)(K/T) from (919 to 1058) K; ErI3(s), log(p/kPa) ) 11.55 ( 0.15 - (13862 ( 200)(K/T) from (871 to 1082) K. Treating the results by second- and third-law methods, the standard sublimation enthalpies were determined to be DsubH°(298 K) ) {(308 ( 4) kJ mol-1 and (293 ( 4) kJ mol-1} for ErCl3 and ErBr3, respectively. For ErI3 the proposed enthalpy, DsubH°(298 K) ) (282 ( 6) kJ mol-1, was only derived by the second-law method. From this standard enthalpy a set of free energy functions for solid ErI3 was evaluated by third-law treatment of the data.