. Can. J. Chem. 56, 1586 (1978). Standard enthalpies of formation of crystalline selenium(1V) halides were determined by solution calorimetry relative to that of selenium(1V) oxide. The values obtained were: AH?.,,, SeCI4(c), -42.7 + 0.4 and Afl,,,, SeBr,(c), -17.9 f 0.5 kcal mol-'. ALAN D. WESTLAND et RAMESH MAKHIJA. Can. J. Chem. 56, 1586(1978. On a determine les enthalpies standard de formation des halogenures cristallins du selenium(1V) en faisant appel a la calorimetric en solution relative aux propriktes de I'oxyde de selenium(1V). On a obtenu les valeurs suivantes:SeCl,(c), -42.7 f 0.4 et A=,,,, SeBr,(c), -17.9 f 0.5 kcal mol-'.[Traduit par le journal]In a study of the enthalpies of reaction of selenium-(IV) halides with the corresponding alkali halides, it was useful to know the standard enthalpies of formation of SeCl,(c) and SeBr,(c). The value -43.8 kcal mol-' is given for the chloride in the most recent tabulation published by the National Bureau of Standards, Washington (1). This value appears to derive from the measurements made by Thornpsen (2) in the last century. His original value has undergone revision because it is now realized that the hexagonal form of selenium is the most stable state (3), whereas Thompsen chose glassy selenium as the standard state. It appeared desirable to repeat the determination by means of an alternative method. There is no reported value of the enthalpy of formation of SeBr,.We have measured both of these enthalpies by solution calorimetry. Thus, a determination of the enthalpy of the process enables us to obtain AHf"for SeCI, from the tabulated enthalpies of formation for the other com- were measured a n d AH, and AH, were evaluated from published data (1).In order for the method to give a correct result, it is necessary that the selenium species in solution b e labile. We were unable to discover from the literature what period of time is required for the oxyhalo species to reach equilibri~~m but the shape of o u r temperature-time plots for the dissolution o f selenium(lV) halides suggested that all enthalpic processes were complete within 2-6 min. Raman spectra indicate that identical solutions result from dissolving either SeCI, or SeO, in hydrochloric acid. ' The relevant equations for the study of SeBr, a r e as follows:pounds in the equation. The partial processes, the = (SeBr, + 320HC1 + 4029HZ0} enthalpies for which were either measured or evaluated from published data, are as follows:
