Europium thermodynamic propertie

This work was undertaken as a part of a study of divalent lanthanide halides in an effort to obtain more accurate thermal data on EuC12 and to determine if the close similarity of the high-temperature thermodynamic properties of divalent europium and alkaline earth compounds emphasized earlier (13-16) could be extended. 

Skochdopole, Griff el, and Spedding 310) have compared measured entropies for the rare earths with theoretically predicted values. Although they do not predict a value for europium, they believe it is somewhat higher than its immediate periodic table neighbors. On this basis, we adopt a value of 17 e. u. for the entropy of europium at 298 K. Spedding and Daane 314) remark that europium is the most volatile of the rare earths. Landolt-Bornstein 208) report available spectroscopic terms from which we have calculated the thermodynamic properties of the ideal monatomic gas. The remaining data listed for this element are estimated and are consistent with the above known facts. These data are intended for use only until measured values become available. 

The thermochemical and thermophysical properties of the rare earth sesquioxides were critically evaluated in 1973 (Gschneidner etal. 1973). A systematic comparison of rare-earth and actinide sesquioxides was published in 1983 (Morss 1983). Thermodynamic properties of europium oxides were assessed by Rard (1985). Since then the enthalpies of formation of AmjOj and CfjOj were determined by solution microcalorimetry. The Afif [Am (aq)] has been redetermined even more recently so the Af//°[Y (aq)] has been corrected in table 4. Recently, the enthalpy of formation of YjOj was redetermined by combustion calorimetry (Lavut and Chelovskaya 1990) and independently by solution calorimetry (Morss et al. 1993). The latter determination took advantage of a determination of Afff [Y (aq)] that used very pure Y metal (Wang et al. 1988). Assessed values are listed in table 4. 

Rard s (1985) assessment of europium thermodynamics included AG = 150.7 5.7 kJ mol(K = 3.9 x 10 ) for the similar solubility equilibrium of Eu(OH)j. From this AG and other thermodynamic properties he calculated AfG [Eu(OH)3(s)] = - 1198.9 7.8k Jmol- and Af/f [EU(OH)3(s)] = - 1336.5 8.3kJmol . Clearly, the calorimetric and equilibrium measurements for these hydroxides need to be reconciled. For actinide hydroxides approach-to-equilibrium measurements have been made the scatter among measurements and estimates indicates that equilibrium may not have been reached (Morss 1992a). One calorimetric measurement of an actinide hydroxide enthalpy of formation has been made (table 4, Morss and Williams 1994) from which K p[Am(OH)3] = 7 x 10 has been calculated. This C p is significantly smaller than that of structurally similar Nd(OH)j. 

The thermochemistry of rare-earth trifluorides was summarized in Gmelin Hand-buch (1976) and the thermochemistry of rare-earth tribromides and triiodides was summarized in Gmelin Handbuch (1978). The thermochemistry of trivalent rare-earth trichlorides was critically assessed by Morss (1976). Enthalpies of formation of most of the lanthanide tribromides were determined by Hurtgen et al. (1980). Thermodynamic properties for europium halides were assessed by Rard (1985). Only enthalpies of formation of Sc, Y, Dy and Tm triiodides have been redetermined since the classical work of Hohmann and Bommer (Morss and Spence 1992). A recent set of literature values of enthalpies of formation of rare-earth solid and gaseous trihalides has been published, accompanied by Born-Haber cycle estimated values for all trihalides (Struck and Baglio 1992). 

The last chapter (134) in this volume is an extensive review by Colinet and Pasturel of the thermodynamic properties of landianide and actinide metallic systems. In addition to compiling useful theiTnodynamic data, such as enthalpies, entropies, and free eneigies of formation and of mixing, the authors have made an extensive comparative analysis of the thermodynamic behavior of the rare earths and actinides when alloyed with metallic elements. They note that when alloyed with non-transition metals, the enthalpies of formation of uranium alloys are less negative than those of the rare earths while those of thorium and plutonium are about the same as the latter. For transition metal alloys the formation enthalpies of thorium and uranium are more negative than diose of the rare earths and plutonium (the latter two are about the same). The anomalous behaviors of cerium, europium and ytterbium in various compounds and alloys are also discussed along with the effect of valence state changes found in uranium and plutonium alloys. 

The insufficiency of the literature data determined the sequence with which the thermodynamic properties of lanthanide halides were considered in our work. We first described RF3 (Chervonnyi and Chervoimaya, 2007a), next RCI3 (Chervoimyi and Chervonnaya, 2007b), and, finally, RCI2 (Chervoimyi and Chervonnaya, 2008a). This description was preceded by complex calculations of thermodynamic equilibria in the case of samarium, europium, and ytterbium chlorides (Chervonnyi and Chervonnaya, 2004a,e,f, 2005b). 

Rao CJ, Venkatesan KA, Nagarajan K et al (2010) Electrochemical and thermodynamic properties of europium(III), samarium(III), and cerium(III) in l-butyl-3-methylimidazolium chloride ionic liquid. J Nucl Mater 399 81-86... 

Standard oxidation potentials referred to the normal hydrogen electrode (E°) for the divalent and trivalent lanthanide aquo ions are given in table 24.8 based primarily on the selected experimental results compiled by Chariot et al. (1971) and the systematic correlations summarized by Nugent (1975). Only Eu and Yb can persist for times of the order of minutes to hours in dilute acid solution, and can be readily produced by reduction of the trivalent ionic species (Laitinen and Taebel, 1941 Laitinen, 1942 Christensen et al., 1973). The value of E° = -0.43 V for the Eu(II-III) couple quoted in many previous compilations was obtained using both potentiometric and polarographic techniques. However, in a reevaluation of the solution thermodynamic properties of europium, Morss and Haug (1973) recommended the value E° = —0.35 V. 

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