| Heats of formation, Gibbs free energies of formation, and heat capacities as a function of temperature are thermodynamic properties of solids often needed in process calculations. Literature data for these properties of many inorganic salts, minerals, clays, and related substances are not available. As greater effort is being directed towards problems such as environmental cleanup, these thermodynamic properties are needed to perform the required process calculations. Two different additive group contribution techniques are developed to provide the additivity constants for the prediction of these properties. The first technique provides values for group additivity constants of anions and cations which combine to form solid inorganic salts where ionic bonds predominate. The second considers oxide and hydroxide groups which combine to form minerals, clays, and related substances with primarily covalent bonds. Multiple linear regression is used to estimate the contributions for each of the required additivity constants. For solid inorganic salts, data from 938, 687, and 664 compounds are used, respectively, to obtain 136 cation and 22 anion additivity constants for heats of formation, 126 cation and 21 anion constants for free energies of formation, and 129 cation and 17 anion sets of constants for heat capacity temperature function coefficients. For minerals, clays, and related solids, data from 190 compounds are used to obtain 44 additivity constants for heats and free energies of formation and from 157 compounds to obtain 42 sets of additivity constants for heat capacities. The average errors in the predictions for solid inorganic salts are 2.57% for heats of formation, 2.60% for free energies of formation, and 3.14% for heat capacities at 298 K. For minerals, clays, and related substances the average errors are 1.00% for heats of formation, 1.01% for free energies of formation, and 1.75%, increasing to 2.95% for heat capacities from 298 K to 800 K, respectively. |
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