Thermodynamics of the Solvation of CaSO4 in Mixed DMF-H2O at 301.15 K
Esam A. Gomaa *
Chemistry Department, Faculty of Science, Mansoura University, 35516-Mansoura, Egypt
Elsayed M. Abou Elleef
Basic Science Department, Delta Higher Institute for Engineering & Technology, 35681- Dalkha, Mansoura, Egypt
M. G. Abdel-Razek
Chemistry Department, Faculty of Science, Mansoura University, 35516-Mansoura, Egypt
*Author to whom correspondence should be addressed.
Abstract
Aims: The aim of this study was to determine the thermodynamics of the solvation of CaSO4 in mixed DMF-H2O at 301.15 K. The Gibbs free energies as very important thermodynamic property were evaluated for CaSO4 in mixed dimethylformamide (DMF)-H2O solvents at 301.15 K from the experimental solubility measurements. The ratio of the ionic radii between calcium and sulphate ions was used to divide the total Gibbs free energy of the salt into its individual contribution in the mixtures used. Libration Gibbs free energy associated with the moving CaSO4 in standard gas state to standard state in solution was evaluated according to specific cycle for the solvation process using the solubility product. Also the lattice energy for solid CaSO4 (cr) was also calculated and used for further evaluation. The conventional Gibbs free energies for the cation (Ca2+) and the anion (SO42-) were estimated theoretically and also the Gibbs free energy of SO42- gas was evaluated and all values were discussed.
Keywords: CaSO4, Gibbs free energy of salvation, calcium sulphate, aqueous- dimethylformamide mixtures, conventional free energies