Standard Molar Gibbs Free Energy Research Articles

Thermodynamic Properties of Diphenylmethane

Measurements leading to the calculation of the standard thermodynamic properties for gaseous diphenylmethane (Chemical Abstracts registry number [101-81-5]) are reported. Experimental methods include adiabatic heat-capacity calorimetry, vibrating-tube densimetry, comparative ebulliometry, inclined-piston gauge manometry, and differential-scanning calorimetry (dsc). Measurement results for the enthalpy of combustion were reported previously. The critical temperature was measured with a differential scanning calorimeter. The critical pressure and critical density were estimated. Standard molar entropies, standard molar enthalpies, and standard molar Gibbs free energies of formation were derived at selected temperatures between 298.15 K and 700 K. All results are compared with experimental values reported in the literature.

Thermodynamics of formation of double salts and mixed crystals from aqueous solutions

This paper describes a chemical model that calculates (solid + liquid) equilibria in the ( m 1CuCl 2 + m 2NiCl 2)(aq), ( m 1MgCl 2 + m 2CrCl 3)(aq), ( m 1(NH 4) 2SO 4 + m 2CuSO 4)(aq), and ( m 1(NH 4) 2SO 4 + m 2MgSO 4)(aq) systems, where m denotes molality at T = 298.15 K. The Pitzer ion-interaction model has been used for thermodynamic analysis of the experimental mixing solutions solubility data, presented in the literature. The thermodynamic functions needed have been calculated and the theoretical solubility isotherms have been plotted. The mixed solution model parameters { θ(MN) and ψ(MNX)} have been chosen on the basis of the compositions of saturated ternary solutions and data on the pure water solubility of the (NH 4) 2SO 4 · CuSO 4 · 6H 2O and (NH 4) 2SO 4 · MgSO 4 · 6H 2O double salts. The results of Pitzer ion interaction model-based thermodynamic studies at T = 298.15 K on 62 binary, 82 ternary and eight multicomponent (water + salt) systems where solid phases with a constant stoichiometric composition (simple and double salts) crystallize have been summarized. The values of the pure electrolyte and mixing ion-interaction parameters, which give the best fit of the activity data in binary solutions and of the ternary solutions solubility data are tabulated. Important thermodynamic characteristics (thermodynamic solubility products K sp ∘ ; standard molar Gibbs free energy of reaction Δ r G m ∘ of the synthesis of the double salts from the corresponding simple salts, components of the ternary solutions; and the standard molar Gibbs free energy of formation Δ f G m ∘ ) of the solids crystallizing from the saturated binary and ternary solutions are given. The Δ f G m ∘ values obtained are compared with those available in the literature. The results of thermodynamic simulation of binary and ternary systems at temperatures differing from the standard (273.15 K and 348.15 K) are presented. The model parameterization is tested by comparison of the predicted and the experimental composition of the invariant points in multicomponent solutions (not used in parameterization process). The component activities of the saturated ( m 1(NH 4) 2SO 4 · CuSO 4 + m 2(NH 4) 2SO 4 · MgSO 4)(aq) and in the mixed crystalline phase were determined and the change of the molar Gibbs free energy of mixing Δ mix G m ∘ ( s ) of crystals was determined as a function of the solid phase composition. It is established that at T = 298.15 K the mixed (NH 4) 2SO 4 · (Cu,Mg)SO 4 · 6H 2O crystals show positive deviations from the ideal mixed crystals. Values for the integral Gibbs free energy of mixing Δ mix G m ∘ ( s ) and excess Gibbs free energy of mixing Δ G m E ( s ) in crystals calculated by different methods for the 23 ternary systems with co-crystallization of the salt components have been summarized.

Thermodynamic Properties of 2-Methylquinoline and 8-Methylquinoline

Measurements leading to the calculation of the standard thermodynamic properties for gaseous 2-methylquinoline (Chemical Abstracts registry number [91-63-4]) and 8-methylquinoline (Chemical Abstracts registry number [611-32-5]) are reported. Experimental methods include oxygen bomb calorimetry, adiabatic heat capacity calorimetry, vibrating-tube densitometry, comparative ebulliometry, inclined-piston gauge manometry, and differential scanning calorimetry (dsc). The critical temperature was measured with a differential scanning calorimeter. The critical pressure and critical density were estimated. Standard molar entropies, standard molar enthalpies, and standard molar Gibbs free energies of formation were derived at selected temperatures between 298.15 K and 700 K. All results are compared with experimental values reported in the literature.

Thermodynamics of monoclinic Fe 2(SO 4) 3

Thermodynamic properties of monoclinic Fe 2(SO 4) 3 were measured by acid solution calorimetry, adiabatic calorimetry, and semi-adiabatic calorimetry. The standard molar enthalpy of formation Δ f H m ∘ was determined as −(2585.2 ± 4.9) kJ · mol −1 by an appropriate thermochemical cycle with enthalpies of solution of monoclinic Fe 2(SO 4) 3, α-MgSO 4, γ-FeOOH, H 2O, and MgO in 5 N HCl at T = 298 K. Heat capacity data were collected from T = (0.5 to 400) K. The standard molar entropy S m ∘ at T = 298.15 K is (305.6 ± 0.6) J · K −1 · mol −1. While the enthalpy of formation agrees well with a previous Δ f H m ∘ determination, the entropy differs significantly because magnetic entropy was entirely overlooked in the previous work. The heat capacity shows a sharp magnetic transition with the peak located at 30.0 K. The C p,m data in the temperature range (273 to 395) K are represented by a Maier–Kelley polynomial C p,m/J · K −1 · mol −1 = 213.0 + 0.3121( T/K) − 2.959 × 10 6( T/K) −2. The calculated standard molar Gibbs free energy of formation from the elements Δ f G m ∘ at T = 298.15 K is −(2264.5 ± 4.9) kJ · mol −1.

Application of solid-state galvanic cells to the thermodynamic study of the CaO–SiO 2–ZrO 2 system

Standard molar Gibbs free energies of formation from the oxides, Δ f G ox°, of Ca 2ZrSi 4O 12 and Ca 3ZrSi 2O 9 have been determined in the temperature range 923 K to 1273 K with the help of solid-state galvanic cells involving calcium β″-alumina electrolyte. The Δ f G ox° values obtained for Ca 2ZrSi 4O 12, have been compared with those by Jacob et al.

Saturation molalities and standard molar enthalpies of solution of 2′-deoxyadenosine · H 2O(cr), 2′-deoxycytidine · H 2O(cr), 2′-deoxyguanosine · H 2O(cr), 2′-deoxyinosine(cr), and 2′-deoxyuridine(cr) in H 2O(l)

Saturation molalities m(sat) in H 2O(l) have been measured for the substances 2′-deoxyadenosine · H 2O(cr), 2′-deoxycytidine · H 2O(cr), 2′-deoxyguanosine · H 2O(cr), 2′-deoxyinosine(cr), and 2′-deoxyuridine(cr) by using h.p.l.c. The states of hydration were established by performing Karl Fischer analyses on samples of these substances, which had been allowed to equilibrate with their respective aqueous saturated solutions for several days at T ≈ 298 K and then dried with air at T ≈ 296 K for ≈24 h. The crystalline forms of the substances were identified by comparison of the results of X-ray diffraction measurements with results from the literature. Also, calorimetric molar enthalpies of solution Δ sol H m(cal) for these substances were measured by using an isoperibol solution calorimeter. A self-association (stacking) model was used to estimate values of the activity coefficients γ and relative apparent molar enthalpies L ϕ for these substances. These γ and L ϕ values were used to adjust the measured values of m(sat) and Δ sol H m to the standard state and thus obtain values of the standard molar Gibbs free energy Δ sol G m ∘ and enthalpy changes Δ sol H m ∘ for the dissolution reactions of these substances. The values of the p Ks and of the standard molar enthalpies of the ionization reactions were also used to account for speciation of the substances in the calculations of Δ sol G m ∘ and Δ sol H m ∘ .

A thermodynamic study of the ketoreductase-catalyzed reduction of 2-alkanones in non-aqueous solvents

Equilibrium constants K have been measured for the reactions (2-alkanone + 2-propanol = 2-alkanol + acetone), where 2-alkanone = 2-butanone, 2-pentanone, 2-hexanone, 2-heptanone, and 2-octanone and 2-alkanol = 2-butanol, 2-pentanol, 2-hexanol, 2-heptanol, and 2-octanol. The solvents used were n-hexane, toluene, methyl tert-butyl ether (MTBE), and supercritical carbon dioxide SCCO 2 (pressure P = 10.0 MPa). The temperature range was T = (288.15 to 308.27) K. Chiral analysis of the reaction products showed that the enzyme used in this study was stereoselective for the 2-octanone reaction system, i.e. only ( S)-(+)-2-octanol was formed. For the reactions involving butanone, pentanone, and hexanone, the products were racemic mixtures of the respective ( S)-(+)-2-alkanol and the ( R)-(−)-2-alkanol. Chiral analysis showed that for the 2-heptanone reaction system, the 2-alkanol product was a mixture of ( S)-(+)-2-heptanol and ( R)-(−)-2-heptanol, at the respective mole fractions of 0.95 and 0.05. The equilibrium constant for the reaction system involving 2-butanone carried out in n-hexane was measured at several temperatures. For this reaction, the values for the thermodynamic reaction quantities at T = 298.15 K are: K = 0.838±0.013; the standard molar Gibbs free energy change Δ r G m ∘ = ( 0.44 ± 0.040 ) kJ · mol - 1 ; the standard molar enthalpy change Δ r H m ∘ = - ( 1.2 ± 1.7 ) kJ · mol - 1 , and the standard molar entropy change Δ r S m ∘ = - ( 5.5 ± 5.7 ) J · K - 1 · mol − 1 . Interestingly, inspection of the values of the equilibrium constants for these reactions carried out in n-hexane, toluene, MTBE, and SCCO 2 shows that these values are comparable and have little dependence on the solvent used to carry out the reaction. The values of the equilibrium constants decrease monotonically with increasing value of the number of carbons N C and trend towards a limiting value of ≈0.30 for N C > 8.

Thermochemistry of 2MgSO 4·MgO·3H 2O

The enthalpy of dissolution of magnesium oxysulfate compound 2MgSO 4·MgO·3H 2O in approximately 1 mol dm −3 aqueous hydrochloric acid was determined. From this result and the enthalpies of dissolution of MgSO 4·7H 2O and MgO in the same solvent and the standard molar enthalpies of formation of MgO(s), MgSO 4·7H 2O(s) and H 2O(l), the standard molar enthalpy of formation of 2MgSO 4·MgO·3H 2O (−4132.07 ± 0.57 kJ mol −1) was calculated. The standard molar entropy of formation of 2MgSO 4·MgO·3H 2O was calculated from the thermodynamic relation with the standard molar Gibbs free energy of formation of 2MgSO 4·MgO·3H 2O that was computed from a group contribution methods.

Possible precursors and products of deep hydrodesulfurization of gasoline and distillate fuels IV. Heat capacities, enthalpy increments, vapor pressures, and derived thermodynamic functions for dicyclohexylsulfide between the temperatures (5 and 520) K

Measurements leading to the calculation of the standard thermodynamic properties for gaseous dicyclohexylsulfide (Chemical Abstracts registry number [7133-46-2]) are reported. Experimental methods include adiabatic heat-capacity calorimetry, and inclined-piston gauge manometry combined with earlier reported measurements of combustion calorimetry, vibrating-tube densitometry, comparative ebulliometry, and differential-scanning calorimetry (d.s.c.). Critical properties are estimated for dicyclohexylsulfide. Standard molar entropies, standard molar enthalpies, and standard molar Gibbs free energies of formation are derived at selected temperatures between (298.15 and 520) K.

Review of the synthesis of layered double hydroxides: a thermodynamic approach

The synthesis of layered double hydroxides (LDHs) by hydrothermal-LDH reconstruction and coprecipitation methods is reviewed using a thermodynamic approach. A mixture model was used for the estimation of the thermodynamics of formation of LDHs. The synthesis and solubility of LDHs are discussed in terms of standard molar Gibbs free energy change of reaction. Data for numerous divalent and trivalent metals as well as for some monovalent and tetravalent metals that may be part of the LDH structure have been compiled. Good agreement is found between theoretical and experimental data. Diagrams and tables for the prediction of possible new LDH materials are provided.

Saturation molalities and standard molar enthalpies of solution of cytidine(cr), hypoxanthine(cr), thymidine(cr), thymine(cr), uridine(cr), and xanthine(cr) in H 2O(l)

Saturation molalities m(sat) in H 2O(l) have been measured for the substances cytidine(cr), hypoxanthine(cr), thymidine(cr), thymine(cr), uridine(cr), and xanthine(cr) by using h.p.l.c. The states of hydration were established by performing Karl-Fischer analyses on samples of these substances, which had been allowed to equilibrate with their respective aqueous saturated solutions for several days at T≈298 K and then dried with air at T≈296 K for ≈24 h. The crystalline forms of the substances were identified by comparison of the results of X-ray diffraction measurements with results from the literature. Also, molar enthalpies of solution Δ sol H m(cal) for these substances were measured by using an isoperibol solution calorimeter. A self-association (stacking) model was used to estimate values of the activity coefficients γ and relative apparent molar enthalpies L φ for these substances. These γ and L φ values were used to adjust the measured values of m(sat) and Δ sol H m(cal) to the standard state and thus obtain values of the standard molar Gibbs free energy Δ sol G ∘ m and enthalpy changes Δ sol H m ∘ for the dissolution reactions of these substances. The values of the p Ks and of the standard molar enthalpies of the ionization reactions were also used to account for speciation of the substances in the calculations of Δ sol G m ∘ and Δ sol H m ∘. Values of standard molar enthalpies of formation Δ f H m ∘, standard molar Gibbs free energies of formation Δ f G m ∘, and standard partial molar entropies S 2,m ∘ for the aqueous species of hypoxanthine and xanthine were calculated. A detailed summary and comparison of thermodynamic results from the literature for these substances is presented.

High-energy components of “designer gasoline and designer diesel fuel” I. Heat capacities, enthalpy increments, vapor pressures, critical properties, and derived thermodynamic functions for bicyclopentyl between the T=(10 and 600) K

Measurements leading to the calculation of the standard thermodynamic properties for gaseous bicyclopentyl (Chemicals Abstracts registry number [1636-39-1]) are reported. Experimental methods include adiabatic heat-capacity calorimetry, comparative ebulliometry, and differential-scanning calorimetry (d.s.c.). The critical temperature was determined by d.s.c. and the critical pressure and critical density were estimated. Standard molar entropies, standard molar enthalpies, and standard molar Gibbs free energies of formation are reported at selected temperatures between T=(298.15 and 600) K. Formation properties were calculated with a literature value for the enthalpy of combustion in the liquid phase. All results are compared with available literature values.

High-energy components of ?designer gasoline and designer diesel fuel? I. Heat capacities, enthalpy increments, vapor pressures, critical properties, and derived thermodynamic functions for bicyclopentyl between the T=(10 and 600) K*1, *2

Measurements leading to the calculation of the standard thermodynamic properties for gaseous bicyclopentyl (Chemicals Abstracts registry number [1636-39-1]) are reported. Experimental methods include adiabatic heat-capacity calorimetry, comparative ebulliometry, and differential-scanning calorimetry (d.s.c.). The critical temperature was determined by d.s.c. and the critical pressure and critical density were estimated. Standard molar entropies, standard molar enthalpies, and standard molar Gibbs free energies of formation are reported at selected temperatures between T =(298.15 and 600) K. Formation properties were calculated with a literature value for the enthalpy of combustion in the liquid phase. All results are compared with available literature values.

Possible precursors and products of deep hydrodesulfurization of gasoline and distillate fuels III. The thermodynamic properties of 1,2,3,4-tetrahydrodibenzothiophene

Measurements leading to the calculation of the standard thermodynamic properties for gaseous 1,2,3,4-tetrahydrodibenzothiophene (Chemical Abstracts registry number [16587-33-0]) are reported. Experimental methods include combustion calorimetry, adiabatic heat-capacity calorimetry, vibrating-tube densitometry, comparative ebulliometry, inclined-piston gauge manometry, and differential-scanning calorimetry (d.s.c.). Critical properties are estimated for 1,2,3,4-tetrahydrodibenzothiophene. Standard molar entropies, standard molar enthalpies, and standard molar Gibbs free energies of formation are derived at selected T between (298.15 and 600) K.

Thermochemistry of hydrated lithium monoborates

The enthalpies of solution of two hydrated lithium monoborates in approximately 1 mol dm −3 aqueous hydrochloric acid were determined. From these results and the enthalpies of solution of H 3BO 3 in approximately 1 mol dm −3 HCl(aq), and of LiCl·H 2O in aqueous(hydrochloric acid + boric acid),combining with the standard molar enthalpies of formation of LiCl·H 2O(s), H 3BO 3(s) and H 2O(l), the standard molar enthalpies of formation of −1627.46±0.90 and −3397.00±0.94 kJ mol −1 for LiBO 2·2H 2O and LiBO 2·8H 2O were obtained. The standard molar entropies of formation of LiBO 2·2H 2O and LiBO 2·8H 2O were calculated from the thermodynamic relation with the standard molar Gibbs free energy of formation of LiBO 2·2H 2O and LiBO 2·8H 2O computed from a group contribution method.

Heat-capacity measurements and thermodynamic functions of crystalline adenine; revised thermodynamic properties of aqueous adenine

The standard molar heat capacity C ∘ p,m of adenine(cr) has been measured using adiabatic calorimetry over the range 6<( T/K)<310 and the results used to derive thermodynamic functions for adenine(cr) at smoothed temperatures. At T=298.15 K, C ∘ p,m=(142.67±0.29) J · K −1 · mol −1 and the third law entropy S ∘ m=(145.62±0.29) J · K −1 · mol −1. The standard molar Gibbs free energy of formation Δ f G ∘ m at T=298.15 K for crystalline adenine was calculated, using the standard molar enthalpy of formation for the compound and entropies of the elements from the literature, and found to be Δ f G ∘ m=(301.4±1.0) kJ · mol −1. The results were combined with solution calorimetry and solubility measurements from the literature to yield revised values for the standard molar thermodynamic properties of aqueous adenine at T=298.15 K: Δ f G ∘ m=(313.4±1.0) kJ · mol −1, Δ f H ∘ m=(129.5±1.4) kJ · mol −1, and S m ∘=(217.68±0.44) J · K −1 · mol −1.

Thermodynamics of formation of double salts M 2SO 4 · M ′SO 4 · 6H 2O and M 2SeO 4 · M ′SeO 4 · 6H 2O where M denotes Rb, or Cs and M ′ denote Co, Ni, or Zn

This paper describes a chemical model that calculates (solid + liquid) equilibria in the ( m 1Rb 2SO 4 + m 2CoSO 4)(aq), ( m 1Rb 2SeO 4 + m 2CoSeO 4)(aq), ( m 1Rb 2SO 4 + m 2NiSO 4)(aq), ( m 1Rb 2SO 4 + m 2ZnSO 4)(aq), ( m 1Rb 2SeO 4 + m 2ZnSeO 4)(aq), ( m 1Cs 2SO 4 + m 2CoSO 4)(aq), ( m 1Cs 2SeO 4 + m 2CoSeO 4)(aq), ( m 1Cs 2SO 4 + m 2NiSO 4)(aq), ( m 1Cs 2SeO 4 + m 2NiSeO 4)(aq), ( m 1Cs 2SO 4 + m 2ZnSO 4)(aq), and ( m 1Cs 2SeO 4 + m 2ZnSeO 4)(aq) systems, where m denotes molality at the temperature T=298.15 K. The Pitzer ion-interaction model has been used for thermodynamic analysis of the experimental osmotic and solubility data presented in the literature. The thermodynamic functions needed (binary and ternary parameters of ionic interaction, thermodynamic solubility products) have been calculated and the theoretical solubility isotherm has been plotted. The mixing parameters { θ(MN) and ψ(MNX)} have been chosen on the basis of the compositions of saturated ternary solutions and data on the binary solubility of the sulfate M 2SO 4. M ′SO 4 · 6H 2O double salts in water. To validate the mixing solutions model two different approaches have been used in evaluation of the ternary parameters: (I) preserving the same value of the binary mixing θ(MN) for the corresponding chloride, bromide, sulfate, and selenate systems with the same cations, and (II) with constant θ(MN) value (set equal to −0.05) for the all 11 sulfate and selenate systems. Very good agreement between experimentally determined and model predicted solubilities has been found. Important thermodynamic characteristics (thermodynamic solubility products, standard molar Gibbs free energy of formation) of the solid phases (simple salts, six sulfate – M 2SO 4 · M ′SO 4 · 6H 2O, and five selenate – M 2SeO 4 · M ′SeO 4 · 6H 2O – double salts) crystallizing in the systems under consideration are determined.

Thermodynamics of the hydrolysis reactions of adenosine 3 ′,5 ′-(cyclic)phosphate(aq) and phospho enolpyruvate(aq); the standard molar formation properties of 3 ′,5 ′-(cyclic)phosphate(aq) and phospho enolpyruvate(aq)

Molar calorimetric enthalpy changes Δ r H m(cal) have been measured for the biochemical reactions {cAMP(aq) + H 2O(l)=AMP(aq)} and {PEP(aq) + H 2O(l)=pyruvate(aq) + phosphate(aq)}. The reactions were catalyzed, respectively, by phosphodiesterase 3 ′,5 ′-cyclic nucleotide and by alkaline phosphatase. The results were analyzed by using a chemical equilibrium model to obtain values of standard molar enthalpies of reaction Δ r H m ∘ for the respective reference reactions {cAMP −(aq) + H 2O(l)=HAMP −(aq)} and {PEP 3−(aq) + H 2O(l)=pyruvate −(aq) + HPO 2− 4(aq)}. Literature values of the apparent equilibrium constants K ′ for the reactions {ATP(aq)=cAMP(aq) + pyrophosphate(aq)}, {ATP(aq) + pyruvate(aq)=ADP(aq) + PEP(aq)}, and {ATP(aq) + pyruvate(aq) + phosphate(aq)=AMP(aq) + PEP(aq) + pyrophosphate(aq)} were also analyzed by using the chemical equilibrium model. These calculations yielded values of the equilibrium constants K and standard molar Gibbs free energy changes Δ r G m ∘ for ionic reference reactions that correspond to the overall biochemical reactions. Combination of the standard molar reaction property values ( K, Δ r H m ∘, and Δ r G m ∘) with the standard molar formation properties of the AMP, ADP, ATP, pyrophosphate, and pyruvate species led to values of the standard molar enthalpy Δ f H m ∘ and Gibbs free energy of formation Δ f G m ∘ and the standard partial molar entropy S m ∘ of the cAMP and PEP species. The thermochemical network appears to be reasonably well reinforced and thus lends some confidence to the accuracy of the calculated property values of the variety of species involved in the several reactions considered herein.

System Tb–Fe–O: thermodynamic properties of ternary oxides using solid-state electrochemical cells

The standard molar Gibbs free energies of formation of TbFeO 3(s) and Tb 3Fe 5O 12(s) have been determined using solid-state electrochemical cell employing different solid electrolytes. The reversible emfs of the following solid-state electrochemical cells have been measured in the temperature range 1050⩽ T/K⩽1250. Cell ( I):(−) Pt/{ TbFeO 3( s)+ Tb 2 O 3( s)+ Fe( s)}// YDT/ CSZ//{ Fe( s)+ Fe 0.95 O( s)}/ Pt(+) Cell ( II):(−) Pt/{ Fe( s)+ Fe 0.95 O( s)}// CSZ//{ TbFeO 3( s)+ Tb 3 Fe 5 O 12( s)+ Fe 3 O 4( s)}/ Pt(+) The oxygen chemical potentials corresponding to the three-phase equilibria involving the ternary oxides have been computed from the emf data. The standard molar Gibbs free energies of formation of solid TbFeO 3 and Tb 3Fe 5O 12 calculated by the least-squares regression analysis of the data obtained in the present study are given by { Δ f G ∘ m ( TbFeO 3, s)/( kJ· mol −1)±3.2}=−1357.5+0.2531·(T/ K); (1050⩽T/ K⩽1548); and { Δ f G ∘ m ( Tb 3 Fe 5 O 12, s)/( kJ· mol −1)±3.5}=−4901.7+0.9997·(T/ K); (1050⩽T/ K⩽1250). The uncertainty estimates for Δ f G ∘ m include the standard deviation in the emf and uncertainty in the data taken from the literature. Based on the thermodynamic information, oxygen potential diagram and chemical potential diagrams were computed for the system Tb–Fe–O at T=1250 K.

Determination of standard molar Gibbs free energy of formation of Bi 2O 3 over a wide temperature range by EMF method

The EMF of the following galvanic cells (I) W, Bi, Bi 2 O 3| CSZ| O 2 (1 atm), RuO 2, Pt (II) W, Bi, Bi 2 O 3| CSZ| O 2 (1 atm), Pt were measured over a wide range of temperature (572 to 1127) K. With O 2 (1 atm) reference and RuO 2 as the electrode material with Pt as electrical lead, measurements were possible at temperatures close to the melting temperature of Bi. Standard Gibbs free energies of formation, Δ f G 0 m of Bi 2O 3(s) (both α and δ phases) and Bi 2O 3(l) were calculated from the emf measurements and are given by the following expressions: Δ f G 0 m 〈 α-Bi 2 O 3〉±0.3 kJ· mol −1=−583.4+0.2938T/ K (572⩽T⩽988 K), Δ f G 0 m 〈 δ-Bi 2 O 3〉±0.4 kJ· mol −1=−543.8+0.2538T/ K (988⩽T⩽1098 K), Δ f G 0 m { Bi 2 O 3}±0.3. kJ· mol −1=−492.4+0.2070T/ K (1098⩽T⩽1127 K). A third law treatment of the data yielded a value of −568.4 ± 0.5 kJ · mol −1 for the enthalpy of formation of Bi 2O 3(s) at T=298.15 K, Δ f H 0 m, 298.15 K 〈 α-Bi 2 O 3〉 , which is in good agreement with the second law estimate of −570.8 ± 0.3 kJ · mol −1.