ISSN print edition: 0366-6352
ISSN electronic edition: 1336-9075
Registr. No.: MK SR 9/7

Published monthly

On the applicability and predictive power of additive equations in the evaluation of standard enthalpies of formation of crystallohydrate salts of rare-earths and actinoides

N.I. Yanakiev

Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, B-1040 Sofia


Abstract: The validity of equations for the additive evaluation of the standard enthalpies of formation (∆Hf°) of crystallohydrates of rare-earth elements and actinoides is established on the basis of experimental data. Rozenfeld's equation, i.e.  ∆Hf°crystallohydrate) =  ∆Hf° (anhydrous salt) + b1 N where N is the hydration value and b1 is the increment for one water molecule, shows the best approximation to the experimental data and offers the best predictive possibilities. For N = b1 is —307.5 kJ mol-1 , for each from the second to the sixth water molecule bx is — 300.4 kJ mol-1, while for any water molecule belonging to the second coordination sphere bx is — 292.9 kJ mol-1 . The present considerations corroborate the previously published conclusion that the experimentally obtained AHf values for crys­talline phosphate dihydrates of 12 rare-earth elements should be recon­sidered. The use of a general increment of low value ( — 297.1 k J mol-1 ) is shown to be one of the causes for considering in the literature some∆Hf° of crystallohydrates as subject to nonlinear changes and lack of additivity. Rozenfeld's equation is also shown to be useful in the rapid check of crystallohydrate ∆Hf° values in the cases where they do not agree with experimental data for other crystallohydrates of the same salt.

Full paper in Portable Document Format: 416a731.pdf


Chemical Papers 41 (6) 731–738 (1987)

Saturday, October 23, 2021

SCImago Journal Rank 2020
XXVIII. International Conference on Coordination and Bioinorganic Chemistry
© 2021 Chemical Papers