Showing papers on "Enthalpy published in 1995"

Thermodynamic Properties of Minerals and Related Substances at 298.15 K and 1 Bar (105 Pascals) Pressure and at Higher Temperatures

Abstract: A report about values for the entropy, molar volume, and for the enthalpy and Gibbs energy of formation for the elements and minerals and substances at 298.15 K.

Chemical mass transfer in magmatic processes IV. A revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid-solid equilibria in magmatic systems at elevated temperatures and pressures

Abstract: A revised regular solution-type thermodynamic model for twelve-component silicate liquids in the system SiO2-TiO2-Al2O3-Fe2O3-Cr2O3-FeO-MgO-CaO-Na2O-K2O-P2O5-H2O is calibrated. The model is referenced to previously published standard state thermodynamic properties and is derived from a set of internally consistent thermodynamic models for solid solutions of the igneous rock forming minerals, including: (Mg,Fe2+,Ca)-olivines, (Na,Mg,Fe2+,Ca)M2 (Mg,Fe2+, Ti, Fe3+, Al)M1 (Fe3+, Al,Si)2TETO6-pyroxenes, (Na,Ca,K)-feldspars, (Mg,Fe2+) (Fe3+, Al, Cr)2O4-(Mg,Fe2+)2 TiO4 spinels and (Fe2+, Mg, Mn2+)TiO3-Fe2O3 rhombohedral oxides. The calibration utilizes over 2,500 experimentally determined compositions of silicate liquids coexisting at known temperatures, pressures and oxygen fugacities with apatite ±feldspar ±leucite ±olivine ±pyroxene ±quartz ±rhombohedral oxides ±spinel ±whitlockite ±water. The model is applicable to natural magmatic compositions (both hydrous and anhydrous), ranging from potash ankaratrites to rhyolites, over the temperature (T) range 900°–1700°C and pressures (P) up to 4 GPa. The model is implemented as a software package (MELTS) which may be used to simulate igneous processes such as (1) equilibrium or fractional crystallization, (2) isothermal, isenthalpic or isochoric assimilation, and (3) degassing of volatiles. Phase equilibria are predicted using the MELTS package by specifying bulk composition of the system and either (1) T and P, (2) enthalpy (H) and P, (3) entropy (S) and P, or (4) T and volume (V). Phase relations in systems open to oxygen are determined by directly specifying the fo2 or the T-P-fo2 (or equivalently H-P-fo2, S-P-fo2, T-V-fo2) evolution path. Calculations are performed by constrained minimization of the appropriate thermodynamic potential. Compositions and proportions of solids and liquids in the equilibrium assemblage are computed.

Thermodynamics of Micelle Formation as a Function of Temperature - A High-Sensitivity Titration Calorimetry Study

Abstract: Summary and Conclusions Titration calorimetry can be used as a routine method for the determination of all thermodynamic quantities for the micellization of surfactant^.'.^^^^-'^ Particularly, the availability of power compensated microtitration calorimeters with high sensitivity has improved the speed and precision of the method.I6 The cmc and the micellization enthalpy can be determined from a single experiment. The temperature dependence of these quantities is easily accessible in the temperature range between 0 and 80 “C. From the temperature dependence of the demicellization enthalpy, udemic, the heat capacity change, ACp,demic, can be directly determined and thus information on the change in hydrophobic contacts upon demicellization can be estimated. The temperature at which the cmc minimum occurs can be determined with great precision from the temperature where AHdemic is zero. The shape of the titration curves also contains information on the aggregation number. A simulation of the titration curves for deoxycholate was attempted using a simple mass action model with a low aggregation number and the association constant and three enthalpic terms as adjustable parameters. The calculations support previous findings that cholates and deoxycholates form micelles with low aggregation numbers.

Thermodynamics and kinetics of the undercooled liquid and the glass transition of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 alloy

Abstract: Differential scanning calorimetry (DSC) was used to determine the thermodynamic functions of the undercooled liquid and the amorphous phase with respect to the crystalline state of the Zr412Ti138Cu125Ni100Be225bulk metallic glass forming alloy The specific heat capacities of this alloy in the undercooled liquid, the amorphous state and the crystal were determined The differences in enthalpy, ∆H, entropy, ∆S, and Gibbs free energy, ∆G, between crystal and the undercooled liquid were calculated using the measured specific heat capacity data as well as the heat of fusion The results indicate that the Gibbs free energy difference between metastable undercooled liquid and crystalline solid, ∆G, stays small compared to conventional metallic glass forming alloys even for large undercoolings Furthermore, the Kauzmann temperature, TK, where the entropy of the undercooled liquid equals to that of the crystal, was determined to be 560 K The Kauzmann temperature is compared with the experimentally observed rate-dependent glass transition temperature, Tg Both onset and end temperatures of the glass transition depend linearly on the logarithm of the heating rate based on the DSC experiments Those characteristic temperatures for the kinetically observed glass transition become equal close to the Kauzmann temperature in this alloy, which suggests an underlying thermodynamic glass transition as a lower bound for the kinetically observed freezing process

Quartz-coesite transition revisited; reversed experimental determination at 500-1200 degrees C and retrieved thermochemical properties

Abstract: We have determined the quartz-coesite transition by reversed experiments in a pistoncylinder apparatus in the range 500-1200 0c. The differencebetween the sample pressure and apparent pressure was calibrated by (1) studying the friction decay in the hysteresis loop defined by the relationship between apparent ("nominal") pressure and piston position in the compression and decompression cycles, and (2) determining the melting temperature of LiCl by DTA in pressure cells similar to those used in the reversal experiments and comparing the results with those determined in the gas apparatus. The equilibrium transition boundary can be expressed as P (kbar) = 21.945 (:to.1855) + 0.006901 (:to.0003)T (K). It is subparallel to, but -1.5 kbar higher than, the transition boundary determined by Bohlen and Boettcher (1982). We have also retrieved the entropy [39.56 :t 0.2 J/(mol. K)] and enthalpy off ormation (-907.25 :t 0.007 kJ/mol) from elements of coesite at 1 bar, 298 K., from our phase-equilibrium data and selected thermochemical data from the literature. From the characteristics of the hysteresis loop we conclude that the often-used practice of maintaining a constant nominal pressure by repeated pressure adjustment during an experiment leads to variation of pressure on the sample.

Thermodynamic and transport properties of sodium liquid and vapor

Abstract: Data have been reviewed to obtain thermodynamically consistent equations for thermodynamic and transport properties of saturated sodium liquid and vapor Recently published Russian recommendations and results of equation of state calculations on thermophysical properties of sodium have been included in this critical assessment Thermodynamic properties of sodium liquid and vapor that have been assessed include: enthalpy, heat capacity at constant pressure, heat capacity at constant volume, vapor pressure, boiling point, enthalpy of vaporization, density, thermal expansion, adiabatic and isothermal compressibility, speed of sound, critical parameters, and surface tension Transport properties of liquid sodium that have been assessed include: viscosity and thermal conductivity For each property, recommended values and their uncertainties are graphed and tabulated as functions of temperature Detailed discussions of the analyses and determinations of the recommended equations include comparisons with recommendations given in other assessments and explanations of consistency requirements The rationale and methods used in determining the uncertainties in the recommended values are also discussed

Solvent isotope effect and protein stability

Abstract: Here we present a comparative study of the stability of several proteins in H2O and D2O as a function of pH/pH*. We show that the substitution of D2O for H2O leads to an increase in the transition temperature and a decrease in the enthalpy of unfolding. The stability of the proteins, however, appears to be largely unchanged as a result of entropic compensation for the decrease in enthalpy. This enthalpy-entropy compensation is attributed to changes in hydration of proteins in D2O compared to H2O. Analysis of thermodynamic data for the transfer of model compounds from H2O to D2O shows that almost all the changes in the enthalpy of unfolding and in the protein-ligand interactions due to water isotopic substitution can be rationalized by changes in hydration of the buried non-polar groups.

Thermodynamics of Denaturation of Barstar: Evidence for Cold Denaturation and Evaluation of the Interaction with Guanidine Hydrochloride

Abstract: Isothermal guanidine hydrochloride (GdnHC1)-induced denaturation curves obtained at 14 different temperatures in the range 273-323 K have been used in conjunction with thermally-induced denaturation curves obtained in the presence of 15 different concentrations of GdnHCl to characterize the thermodynamics of cold and heat denaturation of barstar. The linear free energy model has been used to determine the excess changes in free energy, enthalpy, entropy, and heat capacity that occur on denaturation. The stability of barstar in water decreases as the temperature is decreased from 300 to 273 K. This decrease in stability is not accompanied by a change in structure as monitored by measurement of the mean residue ellipticities at both 222 and 275 nm. When GdnHCl is present at concentrations between 1.2 and 2.0 M, the decrease in stability with decrease in temperature is however so large that the protein undergoes cold denaturation. The structural transition accompanying the cold denaturation process has been monitored by measuring the mean residue ellipticity at 222 nm. The temperature dependence of the change in free energy, obtained in the presence of 10 different concentrations of GdnHCl in the range 0.2-2.0 M, shows a decrease in stability with a decrease as well as an increase in temperature from 300 K. Values of the thermodynamic parameters governing the cold and the heat denaturation of barstar have been obtained with high precision by analysis of these bell-shaped stability curves. The change in heat capacity accompanying the unfolding reaction, ACP, has a value of 1460 f 70 cal mol-' K-' in water. The dependencies of the changes in enthalpy, entropy, free energy, and heat capacity on GdnHCl concentration have been analyzed on the basis of the linear free energy model. The changes in enthalpy (AHl) and entropy (AS), which occur on preferential binding of GdnHCl to the unfolded state, vis-a-vis the folded state, both have a negative value at low temperatures. With an increase in temperature AHl makes a less favorable contribution, while ASi makes a more favorable contribution to the change in free energy (AGJ due to this interaction. The change in heat capacity (ACp,) that occurs on preferential interaction of GdnHCl with the unfolded form has a value of only 53 f 36 cal mol-' K-' M-'. The data validate the linear free energy model that is commonly used to analyze protein stability. An accurate measurement of the stability of a protein, in terms of the free energy of unfolding (AG) is vital for a correct understanding of the physical interactions that stabilize the protein. The reliability of these measurements assumes importance in studies where the stabilizing interac- tions are perturbed either through mutagenesis of the amino acid sequence or through a change in environmental condi- tions. The stability estimate of a protein is very often based on the analysis of denaturant-induced or thermally-induced unfolding transitions, measured either spectroscopically or calorimetrically. In either case, it is necessary to extrapolate the free energy of unfolding to standard conditions, typically 298 K in the absence of denaturant. Extrapolation of thermally-induced transitions is possible if the change in heat capacity that accompanies unfolding is accurately known, and it is important to establish that this thermodynamic parameter is independent of temperature (Privalov et al., 1989).

Enthalpic Contribution to Protein Stability: Insights from Atom-Based Calculations and Statistical Mechanics

Abstract: Publisher Summary This chapter discusses published analyses of protein stability based on model compound data and outlines the assumptions that have been made. The enthalpy of protein folding is considered and a thermodynamic cycle is used to relate the measurements to quantities that can be calculated. The focus is on the enthalpy of denaturation because it is most directly accessible to calculations. The experiments and analysis of Privalov and co-workers, particularly which of Makhatadze and Privalov are considered in detail because these measurements provide the most complete results on the thermodynamics of proteins. The estimates of internal van der Waals and hydrogen bonding contributions to the enthalpy difference between the native and denatured states of the protein are compared with the calculations of the van der Waals and electrostatic terms (the latter includes hydrogen bonding) from an atom-based model. Statistical mechanical calculations and molecular dynamics simulations are used to estimate the difference in solvation enthalpy, as well as the free energy, of the native and unfolded states.

Structures, energetics, and spectra of aqua-sodium(i) : thermodynamic effects and nonadditive interactions

Abstract: Using extensive ab initio calculations including electron correlation, we have studied structures, thermodynamic quantities, and spectra of hydrated sodium ions [Na(H2O)+n (n=1–6)] Various configurations were investigated to find the stable structures of the clusters The vibrational frequency shifts depending on the number of water molecules were investigated along with the frequency characteristics depending on the presence/absence of outer‐shell water molecules The thermodynamic quantities of the stable structures were compared with experimental data available Entropy‐driven structures for n=5 and particularly for n=6 are noted in the calculations, which can explain the peculiar experimental thermal energies On the other hand, the enthalpy effect to maximize the number of hydrogen bonds of the clusters with the surrounding water molecules seems to be the dominant factor to determine the primary hydration number of Na+ in aqueous solution The nonadditive interactions in the clusters are found to be

Thermodynamic study of phase equilibria in the Pb-Sn-Sb system

Abstract: A thermodynamic analysis of the phase equilibria in the Pb-Sn-Sb ternary system was conducted. A regular solution approximation based on a two-sublattice model was adopted to describe the Gibbs energy of formation of the individual phases in the binary and ternary systems. In the case of some component binary systems, the effect of pressure also was considered. Experimental data obtained by differential thermal analysis (DTA) and electron probe microanalysis (EPMA) in the present study, along with literature data on phase boundaries and thermochemical properties, form the basis for the evaluated thermodynamic parameters used in the calculation. Calculated and experimental phase boundaries agree fairly well.

Thermodynamic properties of α‐quartz, coesite, and stishovite and equilibrium phase relations at high pressures and high temperatures

Abstract: Isobaric heat capacities of α -quartz, coesite, and stishovite were measured by differential scanning calorimetry at 183–703 K. The heat capacity data of coesite represent a significant revision of the previous data. The heat capacities and entropies were also calculated using Kieffer's model. By high-temperature solution calorimetry, transition enthalpy for the β-quartz-coesite at 979 K was measured to be 1.27±0.39 kJ/mol. The enthalpies for the α-quartz-coesite and coesite-stishovite transitions at 298 K were measured to be 3.40±0.56 and 33.62±1.01 kJ/mol, respectively, by differential drop-solution calorimetry. The enthalpy of the coesite-stishovite transition obtained in this study is about 10–15 kJ/mol smaller than those in the previous studies. Phase relations in SiO2 at high pressures and high temperatures were calculated using these new thermodynamic data. The calculated boundary for the α-quartz-coesite transition is consistent with those determined experimentally. For the coesite-stishovite transition, the calculated boundary having a slope of 2.5±0.3 MPa/K disagrees with that by Yagi and Akimoto but is generally consistent with that by Zhang et al.'s new in situ X ray diffraction study.

Thermodynamics of the Hydrothermal Synthesis of Calcium Titanate with Reference to Other Alkaline-Earth Titanates

Abstract: A thermodynamic model for hydrothermal synthesis of alkaline-earth titanates has been utilized to predict the optimum conditions for the synthesis of phase-pure CaTiO3. The predictions have been experimentally validated using Ca(N03)2 or Ca(OH)2 as sources of calcium and crystalline or hydrous T i 0 2 as a source of titanium at moderate temperatures (433-473 K). Practical experimental techniques have been developed to avoid the contamination of the calcium titanate with undesirable solid phases (e.g., calcium carbonate or hydroxide). These conditions were compared with those previously determined for the Ba-Ti and Sr-Ti hydrothermal systems.

Comprehensive Thermodynamic Approach to Modeling Refrigerant-Lubricating Oil Mixtures

Abstract: A comprehensive thermodynamic approach for modeling mixtures of refrigerants and lubricating oils is presented. The new approach includes generalized methods for predicting the following thermodynamic properties of refrigerant-oil mixtures: bubble point temperatures, local oil concentrations, liquid specific heats and enthalpy changes during evaporation. Using this comprehensive method, heat release (enthalpy) curves are easily generated and also the effect of oil on the LMTD (log mean temperature difference) of evaporators can be modeled. Importantly, the definition of the boiling heat-transfer coefficient based on the bubble point temperature is included in the method. This new approach provides the basis for advances to be made in two-phase refrigeration heat-transfer research and design.

Adsorption of Branched and Cyclic Paraffins in Silicalite. 1. Equilibrium

Abstract: Gravimetric equilibrium isotherms are reported for adsorption of branched and cyclic C[sub 6] paraffins on silicalite. In addition to the isotherms, Henry constants and heats of adsorption are reported for 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, methylcyclopentane, and cyclohexane. Adsorption capacities are in the range of 4--7 wt%. All isotherms are of type 1 in Brunauer's classification. Adsorption saturation limits, estimated from the experimental results by Langmuir regression, show a decreasing trend with increasing temperature. Adsorption equilibrium constants follow the trend double-branched < single-branched < cyclic paraffins. Heats of adsorption for the single-branched paraffins increase slightly with loading, but for the double-branched and cyclic paraffins the variation of heat of adsorption with coverage is more pronounced.

Determination of Thermodynamic and Kinetic Parameters from Isothermal Heat Conduction Microcalorimetry: Applications to Long-Term-Reaction Studies

Abstract: The application of heat conduction isothermal microcalorimetry has been proposed for some time as a rapid and general technique for the determination of both thermodynamic and kinetic parameters of chemical reactions These applications have been suggested as being of particular relevance to solid-state reactions and, industrially important, to the prediction of long-term stability and of compatibility data for pharmaceutical materials However, there has yet to be the development of a general procedure that does not require additional noncalorimetric data and that is free of assumptions, which can be used to determine the thermodynamic and kinetic parameters for a reaction, from calorimetric data It is the purpose of this paper to describe such a general approach which does not depend upon knowledge of initial concentrations (quantity), enthalpy, or any predetermined reaction order Equations have been developed whch incorporate calorimetrically accessible data (a, the power, and q, the heat output) and which also include the rate constant, k, the change in enthalpy of the reaction, AH, and the order of reaction A second procedure is also described which depends only on the analysis of the calorimetric signal and which involves no formal chemical kinetic based equations The methods described allow estimation of, for example, the annual extent of degradation of a solid compound The methods developed have been tested through examination of both calculated and experimental data The experimental work examined very slow reactions (lifetime of years) of known order (there are little reliable enthalpy data available for slow reactions) and involved calorimetric observation of these reactions for up to 50 h In all cases, the method yielded the appropriate, Le, conforms to literature data, rate constant, reaction order, and, where available, reaction enthalpy Some situations in which this microcalorimetric approach and subsequent data analysis will be of utility are discussed

Salt effects on polyelectrolyte–ligand binding: Comparison of Poisson–Boltzmann, and limiting law/counterion binding models

Abstract: The theory for the salt dependence of the free energy, entropy, and enthalpy of a polyelectrolyte in the PB (PB) model is extended to treat the nonspecific salt dependence of polyelectrolyte–ligand binding reactions. The salt dependence of the binding constant (K) is given by the difference in osmotic pressure terms between the react ants and the products. For simple 1-1 salts it is shown that this treatment is equivalent to the general preferential interaction model for the salt dependence of binding [C. Anderson and M. Record (1993) Journal of Physical Chemistry, Vol. 97, pp. 7116–7126]. The salt dependence, entropy, and enthalpy are compared for the PB model and one specific form of the preferential interaction coefficient model that uses counterion condensation/limiting law (LL) behavior. The PB and LL models are applied to three ligand–polyelectrolyte systems with the same net ligand charge: a model sphere–cylinder binding reaction, a drug–DNA binding reaction, and a protein–DNA binding reaction. For the small ligands both the PB and limiting law models give (ln K vs. In [salt]) slopes close in magnitude to the net ligand charge. However, the enthalpy/entropy breakdown of the salt dependence is quite different. In the PB model there are considerable contributions from electrostatic enthalpy and dielectric (water reorientation) entropy, compared to the predominant ion cratic (release) entropy in the limiting law model. The relative contributions of these three terms in the PB model depends on the ligand: for the protein, ion release entropy is the smallest contribution to the salt dependence of binding. The effect of three approximations made in the LL model is examined: These approximations are (1) the ligand behaves ideally, (2) the preferential interaction coefficient of the polyelectrolyte is unchanged upon ligand binding, and (3) the polyelectrolyte preferential interaction coefficient is given by the limiting law/counterion-condensation value. Analysis of the PB model shows that assumptions 2 and 3 break down at finite salt concentrations. For the small ligands the effects on the slope cancel, however, giving net slopes that are similar in the PB and LL models, but with a different entropy/enthalpy breakdown. For the protein ligand the errors from assumptions 2 and 3 in the LL model do not cancel. In addition, the ligand no longer behaves ideally due to its complex structure and charge distribution. Thus for the protein the slope is no longer related simply to the net ligand charge, and the PB model gives a much larger slope than the LL model. Additionally, in the PB model most of the salt dependence of the protein binding comes from the change in ligand activity, i.e. from nonspecific anion effects, in contrast to the small ligand case. While the absolute binding is sensitive to polyelectrolyte length, little length effect is seen on the salt dependence for the small ligands at 0.1M salt, and for lengths > 60 A. Almost no DNA length dependenceis seen in the salt dependence of the protein binding, since this is determined primarily by the protein, not the DNA. © 1995 John Wiley & Sons, Inc.

Hydrothermal Precipitation of Lead Zirconate Titanate Solid Solutions: Thermodynamic Modeling and Experimental Synthesis

Abstract: A previously developed thermodynamic model of hydro-thermal synthesis of ceramic powders has been extended to include cases when solid solutions are formed. The model has been applied to the synthesis of a series of lead titanate zirconate solid solutions PbZrxTi1–xO3 (PZT, 0.46 < x≤ 0.75). It predicts the optimum conditions (i.e., reagent, concentration, pH, and temperature) for the precipitation of phase-pure homogeneous PZT, provided that the reactants are well mixed. The predictions have been experimentally corroborated using coprecipitated hydrous oxide ZrxTi1–xC2nH2O (0.46 < x≤ 0.75), as a precursor for Ti and Zr and water-soluble lead acetate or nitrate salts as a source for Pb. When mixtures of hydrous oxides ZrO2·nH2O and TiO2·nH2O were employed as Ti and Zr precursors, independent PbTiO3 and PbZrO3 precipitates rather than the PZT solid solutions formed. These results can be rationalized on the basis of reaction kinetics where thermodynamic modeling includes or excludes the possibility of solid-solution formation.

Criteria for local equilibrium in a system with transport of heat and mass

Abstract: Nonequilibrium molecular dynamics is used to compute the coupled heat and mass transport in a binary isotope mixture of particles interacting with a Lennard-Jones/spline potential. Two different stationary states are studied, one with a fixed internal energy flux and zero mass flux, and the other with a fixed diffusive mass flux and zero temperature gradient. Computations are made for one overall temperature,T=2, and three overall number densities,n=0.1, 0.2, and 0.4. (All numerical values are given in reduced, Lennard-Jones units unless otherwise stated.) Temperature gradients are up to ∇T=0.09 and weight-fraction gradients up to ∇w1=0.007. The flux-force relationships are found to be linear over the entire range. All four transport coefficients (theL-matrix) are determined and the Onsager reciprocal relationship for the off-diagonal coefficients is verified. Four different criteria are used to analyze the concept of local equilibrium in the nonequilibrium system. The local temperature fluctuation is found to be δT≈0.03T and of the same order as the maximum temperature difference across the control volume, except near the cold boundary. A comparison of the local potential energy, enthalpy, and pressure with the corresponding equilibrium values at the same temperature, density, and composition also verifies that local equilibrium is established, except near the boundaries of the system. The velocity contribution to the BoltzmannH-function agrees with its Maxwellian (equilibrium) value within 1%, except near the boundaries, where the deviation is up to 4%. Our results do not support the Eyring-type transport theory involving jumps across energy barriers; we find that its estimates for the heat and mass fluxes are wrong by at least one order of magnitude.

Application of a Multicomponent Thermodynamic Model to Activities and Thermal Properties of 0-40 mol kg-1 Aqueous Sulfuric Acid from <200 to 328 K

Abstract: A multicomponent mole-fraction-based thermodynamic model has been fitted to osmotic coefficients, electromotive force measurements, degrees of dissociation of the HSO 4 - ion, differential heats of dilution, heat capacities, freezing points, and tabulated partial molal enthalpies of water for aqueous H 2 SO 4 , from <200 TO 328 K AND FROM 0 TO 40 MOL KG -1 at 1 atm pressure (1 atm=101.325 kPa). The solution is treated as the mixture H + -HSO 4 - -SO 4 2- -H 2 O. The equations yield a self-consistent representation of activities, speciation, and thermal properties which, for practical applications, is readily extended to more complex mixtures

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

Abstract: 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.