Estimation of the Standard Free Energy of Formation of Metal Arsenates, Selenates, and Selenites
- M. E. Essington
An empirical method developed for estimating the standard free energy of formation (ΔG°f) of solid phases is evaluated for metal arsenates, selenates, and selenites. A free energy function of a solid phase is found to be linearly correlated to a function of the metal oxide ΔG°f and the aqueous metal ion ΔG°f for the compound groups examined. The values estimated by this method are, on average, within ± 10.9, 10.4, and 12.0 kJ mol−1 of the experimental arsenate, selenate, and selenite values, respectively. A method for estimating the ΔG°f of hydrated metal arsenates and selenites is also evaluated. The estimated standard free energy of formation values of hydrated arsenates and selenites, on average, are within ± 23.7 and 10.0 kJ mol−1, respectively, of the observed values. The error involved in estimating metal arsenate, selenate, and selenite ΔG°f values are comparable to those obtained when the estimation technique was applied to other compound types.
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