Vapor Pressure and Sublimation Enthalpies of Holmium Trichloride, Tribromide, and Triiodide

Abstract

The total vapor pressure of HoCl 3 , HoBr 3 , and HoI 3 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: HoCl 3 (s), log(p/kPa) ) 10.91 ( 0.10 -(14216 ( 150) (K/T) (from 883 to 994 K); HoCl 3 (1), log(p/ kPa) ) 9.16 ( 0.10 -(12466 ( 150) (K/T) (from 1002 to 1164 K); HoBr 3 (s) log(p/kPa) ) 10.95 ( 0.10 -(14168 ( 150) (K/T) (from 904 to 1105 K); HoI 3 (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 HoCl 3 and HoBr 3 , ∆ sub H°(298 K) ) 296 ( 10 and 290 ( 5 kJ‚mol -1 , respectively, were derived. For HoI 3 the proposed enthalpy, ∆ sub H°(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 HoI 3 was evaluated by a third-law treatment of the data.

Standard Sublimation Enthalpies of Erbium Trichloride, Tribromide, and Triiodide

“…This average value agrees with that selected by Gietmann et al, , (288.2 ± 6.1) kJ·mol -1 , obtained from the second-law, (293 ± 7) kJ·mol -1 , and third-law, (279 ± 10) kJ·mol -1 , values. Our selected value seems to be decidedly comparable with those obtained by us for tribromides of other heavy lanthanides: GdBr 3 = (292 ± 2), TbBr 3 = (287 ± 4), DyBr 3 = (289 ± 6), and HoBr 3 = (290 ± 5) kJ·mol -1 7 Comparison of the free energy function for solid lanthanide triiodides reported by Pankratz: 19 (▪) LaI 3 ; (○) CeI 3 ; (·) PrI 3 ; (▵) NdI 3 ; (▴) GdI 3 ; (×) TbI 3 ; (□) HoI 3 (Piacente et al); (◇) ErI 3 (this work). 6 Free Energy Function for Solid ErI 3 Calculated by the Third-Law Method, Δ s ub H °(298 K) = (282 ± 6) kJ·mol -1 ( p ° = 1 atm = 101.325 kPa) − R ln( p /atm)−Δfef−fef(g) a −fef(s) T p KkPaJ·K -1 · mol -1 J·K -1 · mol -1 J·K -1 · mol -1 J·K -1 · mol -1 900 1.40 × 10 -4 112.2 201 467.4 266 950 9.05 × 10 -4 96.6 200 470.4 270 1000 4.86 × 10 -3 82.7 200 473.3 273 1050 2.22 × 10 -2 70.0 199 476.2 277 1100 8.84 × 10 -2 58.6 198 479.0 281 a Selected by Pankratz …”

“…Comparison of the free energy function for solid lanthanide triiodides reported by Pankratz: 19 (▪) LaI 3 ; (○) CeI 3 ; (·) PrI 3 ; (▵) NdI 3 ; (▴) GdI 3 ; (×) TbI 3 ; (□) HoI 3 (Piacente et al); (◇) ErI 3 (this work).…”

“…The vaporization behavior of erbium trihalides was considered to be coherent and similar to that of the other rare earth trihalides; − thus, the monomer forms were assumed to be the abundant species present in the vapor above erbium trihalides and their vapor pressures were assumed to be equal to the values of the measured total pressures. In this way, the second-law sublimation or vaporization enthalpies for these compounds in the monomer form at the midrange experimental temperatures were calculated from the slopes of the selected pressure−temperature equations (eqs 1−3).…”

“…The vapor pressure of erbium triiodide was measured by Hirayama et al 6 by the Knudsen method, and the derived standard sublimation enthalpy ∆ sub H°(298 K) ) (306.3 ( 5.0) kJ‚mol -1 is in fair agreement with the value (290 ( 16 kJ‚mol -1 ) obtained by the same authors in a subsequent mass-spectrometric investigation. 7 On this basis, in the context of a continuing research program on the study of the vaporization of lanthanide trihalides (except for trifluorides) [8][9][10][11][12][13][14][15] carried out in our laboratory, the vapor pressures of erbium trihalides were measured by the torsion-effusion method, from which the corresponding standard sublimation enthalpies were derived.…”

Vapor Pressures and Standard Sublimation Enthalpies for Thulium Trichloride, Tribromide, and Triiodide

“…5 The mass spectrum of the vapor over TmI 3 was determined at 913 K, 6 and this was very similar to those of other triiodides of the rare-earth elements. 7 This work is part of a continuing systematic study [8][9][10][11][12][13][14][15][16] carried out in order to obtain accurate measurements of the vapor pressures of rare-earth trihalides and to derive their standard sublimation enthalpies. In particular, the aim of the present paper was to determine the standard sublimation enthalpies of thulium trichloride, tribromide, and triiodide measuring their vapor pressures.…”