MadSci Network: Chemistry

Re: What are the lattice enthalpy and/or hydration enthalpy for divalent anions

Date: Tue Mar 7 04:24:56 2000
Posted By: Werner Sieber, Research Scientist, Pigment Division, Ciba Specialty Chemicals Corp.
Area of science: Chemistry
ID: 951843855.Ch

Dear Mr. McLaughlin,

The tissue of scientific knowledge, on closer inspection, is full of 
holes. In contrast to alkali halides, the determination of lattice 
enthalpies (or energies) of sulfates and carbonates is complicated by the 
following factors: these ions don't exist in the gaseous state, nor do the 
corresponding uncharged molecules. The ions are only coarsely approximated 
by point charges. The crystal structures of the salts are non-cubic and 
polymorphous. At room temperature, crystalline hydrates (with structures 
different from the anhydrous forms) are the equilibrium phases in contact 
with water. Of course, all this would not prevent a dedicated experimental 
scientist from getting the results, but the summed uncertainties would 
probably reduce the utility of the final value. Quite generally, hydration 
enthalpies of anions are lower than those of cations. 
In "Gmelins Handbuch der anorganischen Chemie", 21, Natrium, 
Ergaenzungsband , Lieferung 3, Verlag Chemie GmbH, Weinheim/Bergstr., 
1966, p. 1092, for Na2SO4, values of the lattice energy U, calculated by 
Russian scientists (K.B. Yatsimirsky, J. Gen. Chem. USSR 26 (1956)) are 
given as 470 and 485 kcal/mol, depending on the Kapustinsky-equation used. 
The lattice entropy is 98cal/ For Na2CO3, on page 1320, we find 
U=535 kcal/mol, and delta S= 97cal/mol.deg. I don't know the type of 
approximations involved in the Kapustinsky equation..
Best regards
Werner Sieber

Current Queue | Current Queue for Chemistry | Chemistry archives

Try the links in the MadSci Library for more information on Chemistry.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2000. All rights reserved.