The thermodynamics of aqueous trivalent rare earth elements. Apparent molar heat capacities and volumes of Nd(ClO4)3(aq), Eu(ClO4)3(aq), Er(ClO4)3(aq), and Yb(ClO4)3(aq) from the temperatures 283 K to 328 K

✍ Scribed by Caibin Xiao; Peter R. Tremaine

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 337 KB
• Volume: 29
• Category: Article
• ISSN: 0021-9614
• DOI: 10.1006/jcht.1997.0195

✦ Synopsis

The apparent molar heat capacities and apparent molar volumes of Nd(ClO4)3(aq), Eu(ClO4)3(aq), Er(ClO4)3(aq), and Yb(ClO4)3(aq) have been measured at the temperatures T = (283.2, 298.2, 313.2, and 328.2) K and molalities from 10.05 mol•kg -1 to 10.7 mol•kg -1 in a Picker flow microcalorimeter and vibrating tube densimeter. The results were analysed by means of the Pitzer equations to derive standard partial molar heat capacities C °p,2, standard partial molar volumes V °2 and expressions for the excess properties. The revised Helgeson-Kirkham-Flowers (HFK) model has been used to represent the temperature dependence of the standard partial molar properties within the experimental uncertainty. Plots of C °p,2 and V °2 at T = 298.15 K against the ionic radii of La 3+ , Nd 3+ , Eu 3+ , Er 3+ , Gd 3+ , and Yb 3+ clearly display the discontinuous behaviour known as the ''gadolinum break''. The ionic-radius dependence of the standard partial molar volumes is consistent with changes in the primary hydration number. The effect of temperature on the behaviour of the standard partial molar heat capacities across the series suggests that secondary sphere hydration has a major effect on the values observed for C °p,2. 7 1997 Academic Press Limited KEYWORDS: apparent molar heat capacity; apparent molar volume; standard partial molar properties; aqueous lanthanide(III) ion; solvation

Cp,f,2{Ln(ClO4)3} J•K -1 •mol -1 Nd(ClO4)3; T = 283.2 K 0.