Thermodynamic Properties of the Aqueous Ions (2+ and 3+) of Iron and the Key Compounds of Iron

Recommended thermochemical property values, ΔfH°, ΔfG°, and S° for the aqueous ions of iron, Fe2+ and Fe3+, are given at 298.15 K in SI units. They are consistent with the CODATA Key Values for Thermodynamics. The values are: ΔfH°=−90.0±0.5 kJ⋅mol−1, ΔfG°=−90.53±1.0 kJ⋅mol−1, S°=−101.6±3.7 J⋅mol−1⋅K−1 for Fe2+(ao) and ΔfH°=−49.0±1.5 kJ⋅mol−1, ΔfG°=−16.28±1.1 kJ⋅mol−1, S° =−278.4±7.7 J⋅mol−1⋅K−1 for Fe3+(ao). The evaluation involves the analysis of the enthalpy changes, Gibbs energy changes, and the entropy measurements for all key substances in the key network. A consistent set of thermochemical property values is given for FeOOH(cr, Goethite), FeCl2(cr), FeCl3(cr), FeBr2(cr), FeBr3(cr), FeI2(cr), and FeSO4⋅7H2O(cr), as well as ‘‘reconstituted’’ recommended process values with uncertainties involving these substances. All recommended values are also given for a standard state of p°=1 atm. A computer based reaction catalog of measurements accompanies the text analysis.