The thermodynamic properties of DyBr3(s) and DyI3(s) from T=5 K to their melting temperatures

Low-temperature calorimetric measurements have been performed on DyBr₃(s) in the temperature range (5.5 to 420 K ) and on DyI₃(s) from T=4 K to T=420 K. The data reveal enhanced heat capacities below T=10 K, consisting of a magnetic and an electronic contribution. From the experimental data on DyBr₃(s) a C⁰_p,m (298.15 K) of (102.2±0.2) J·K⁻¹·mol⁻¹ and a value for {S⁰_m (298.15 K) − S⁰_m (5.5 K)} of (205.5±0.5) J·K⁻¹·mol⁻¹, have been obtained. For DyI₃(s), {S⁰_m (298.15 K) − S⁰_m (4 K)} and C⁰_p,m (298.15 K) have been determined as (226.9±0.5) J·K⁻¹·mol⁻¹ and (103.4±0.2) J·K⁻¹·mol⁻¹, respectively. The values for {S⁰_m (5.5 K) − S⁰_m (0)} for DyBr₃(s) and {S⁰_m (4 K) − S⁰_m (0)} for DyI₃(s) have been calculated, giving S⁰_m (298.15 K)=(212.3±0.9) J·K⁻¹·mol⁻¹ in case of DyBr₃(s) and S⁰_m (298.15 K) =(233.1±0.7) J·K⁻¹·mol⁻¹ for DyI₃(s). The high-temperature enthalpy increment has been measured for DyBr₃(s) in the temperature range (525 to 799 K) and for DyI₃(s) in the temperature range (525 to 627 K). From the results obtained and enthalpies of formation from the literature, thermodynamic functions for DyBr₃(s) and DyI₃(s) have been calculated from T→0 to their melting temperatures at 1151.0 K and 1251.5 K, respectively.     

Thermochemical and structural properties of DMAN-“proton sponges”

We report a study on the energetics and structural properties of naphthalene-based proton sponges and their corresponding protonated cations. In particular, we have determined the experimental standard enthalpies of formation in the gas phase at T = 298.15 K, ${\mathrm{\Delta }}_{\text{f}}{H}_{\text{m}}^{\text{o}}$(g), for the neutral and protonated DMAN [1,8-bis (dimethylamino)-naphthalene], (221.0 ± 7.3) and (729.0 ± 11.1) kJ·mol⁻¹, respectively. A reliable experimental estimation of enthalpy associated with “strain” effect and hydrogen bond intramolecular (included within “enhanced basicity”, EB) contributions to the basicity of DMAN, were deduced from isodesmic reactions, −(29.1 ± 4.6) and (87.1 ± 11.9) kJ·mol⁻¹, respectively. The gas-phase basicities (GB) of naphthalene-based proton sponges are compared with the corresponding aqueous basicities (pK_a), covering a range of 149 kJ·mol⁻¹ in GB and 11.5 in pK_a. Density functional calculations at the M05-2X/6-311++G(d,p) level of theory were used to check the consistency of the experimental results and also to estimate the unavailable GB values of the considered species.     

The molar enthalpies of solution and vapour pressures of saturated aqueous solutions of some cesium salts

Vapour pressures of water over saturated solutions of cesium chloride, cesium bromide, cesium nitrate, cesium sulfate, cesium formate, and cesium oxalate were determined as a function of temperature. These vapour pressures were used to evaluate the water activities, osmotic coefficients and molar enthalpies of vapourization. Molar enthalpies of solution of cesium chloride, Δ_solH_m(T = 295.73 K; m = 0.0622 mol · kg⁻¹) = (17.83 ± 0.50) kJ · mol⁻¹; cesium bromide, Δ_solH_m(T = 293.99 K; m = 0.0238 mol · kg⁻¹) = (26.91 ± 0.59) kJ · mol⁻¹; cesium nitrate, Δ_solH_m(T = 294.68 K; m = 0.0258 mol · kg⁻¹) = (37.1 ± 2.3) kJ · mol⁻¹; cesium sulfate, Δ_solH_m(T = 296.43 K; m = 0.0284 mol · kg⁻¹) = (16.94 ± 0.43) kJ · mol⁻¹; cesium formate, Δ_solH_m(T = 295.64 K; m = 0.0283 mol · kg⁻¹) = (11.10 ± 0.26) kJ · mol⁻¹ and Δ_solH_m(T = 292.64 K; m = 0.0577 mol · kg⁻¹) = (11.56 ± 0.56) kJ · mol⁻¹; and cesium oxalate, Δ_solH_m(T = 291.34 K; m = 0.0143 mol · kg⁻¹) = (22.07 ± 0.16) kJ · mol⁻¹ were determined calorimetrically. The purity of the chemicals was generally greater than 0.99 mass fraction, except for HCOOCs and (COOCs)₂ where purities were approximately 0.95 and 0.97 mass fraction, respectively. The uncertainties are one standard deviations.     

Thermodynamics of the oxidation–reduction reaction {2 glutathionered(aq) + NADPox(aq)=glutathioneox(aq) + NADPred(aq)}

Microcalorimetry, spectrophotometry, and high-performance liquid chromatography (h.p.l.c.) have been used to conduct a thermodynamic investigation of the glutathione reductase catalyzed reaction {2 glutathione_red(aq) + NADP_ox(aq)=glutathione_ox(aq) + NADP_red(aq)}. The reaction involves the breaking of a disulfide bond and is of particular importance because of the role glutathione_red plays in the repair of enzymes. The measured values of the apparent equilibrium constant K^′ for this reaction ranged from 0.5 to 69 and were measured over a range of temperature (288.15 K to 303.15 K), pH (6.58 to 8.68), and ionic strength I_m (0.091 mol · kg⁻¹ to 0.90 mol · kg⁻¹). The results of the equilibrium and calorimetric measurements were analyzed in terms of a chemical equilibrium model that accounts for the multiplicity of ionic states of the reactants and products. These calculations led to values of thermodynamic quantities at T=298.15 K and I_m=0 for a chemical reference reaction that involves specific ionic forms. Thus, for the reaction {2 glutathione_red⁻(aq) + NADP_ox³⁻(aq)=glutathione_ox²⁻(aq) + NADP_red⁴⁻(aq) + H⁺(aq)}, the equilibrium constant K=(6.5±4.4)·10⁻¹¹, the standard molar enthalpy of reaction Δ_rH^o_m=(6.9±3.0) kJ · mol⁻¹, the standard molar Gibbs free energy change Δ_rG^o_m=(58.1±1.7) kJ · mol⁻¹, and the standard molar entropy change Δ_rS^o_m=−(172±12) J · K⁻¹ · mol⁻¹. Under approximately physiological conditions (T=311.15 K, pH=7.0, and I_m=0.25 mol · kg⁻¹ the apparent equilibrium constant K^′≈0.013. The results of the several studies of this reaction from the literature have also been examined and analyzed using the chemical equilibrium model. It was found that much of the literature is in agreement with the results of this study. Use of our results together with a value from the literature for the standard electromotive force E^o for the NADP redox reaction leads to E^o=0.166 V (T=298.15 K and I=0) for the glutathione redox reaction {glutathione_ox²⁻(aq) + 2 H⁺(aq) + 2 e⁻=2 glutathione_red⁻(aq)}. The thermodynamic results obtained in this study also permit the calculation of the standard apparent electromotive force E^′o for the biochemical redox reaction {glutathione_ox(aq) + 2 e⁻=2 glutathione_red(aq)} over a wide range of temperature, pH, and ionic strength. At T=298.15 K, I=0.25 mol · kg⁻¹, and pH=7.0, the calculated value of E^′o is −0.265 V.     

Thermochemistry of some barium compounds

The molar enthalpies of reaction of metallic barium with 0.047 mol·dm⁻³ HClO₄ as well as the molar enthalpies of dissolution of BaCl₂ in 1.01 mol·dm⁻³ HCl and in water have been measured at T=298.15 K in a sealed swinging calorimeter with an isothermal jacket. From these results the standard molar enthalpy of formation of the barium ion in an aqueous solution at infinite dilution, as well as the enthalpies of formation of barium chloride and barium perchlorate, are calculated to be: Δ_fH⁰_m(Ba²⁺,aq)=−(535.83±1.25) kJ · mol⁻¹; Δ_fH⁰_m(BaCl₂,cr)=−(855.66±1.28) kJ · mol⁻¹; and Δ_fH⁰_m(BaClO₄,cr)=−(796.26±1.35) kJ · mol⁻¹. The results obtained are discussed and compared with previous experimental values.     

The investigation of thermodynamic parameters of kinetic reaction between o-phenylenediamine and gold (III)

A visible spectrophotometric method has been developed for the reaction kinetics of o-phenylenediamine in the presence of gold (III). The method is based on the measurement of the absorbance of the reaction o-phenylenediamine and gold (III). Optimum conditions for the reaction were established as pH 6 at λ = 466 nm.When the reaction kinetic of o-phenylenediamine by gold (III) was investigated, it was observed that the following rate formula was found as ln (A/A₀) = −kt, according to absorbance measurements. The activation energy E_a and Arrhenius constant A were calculated from the Arrhenius equation as 1.009 kJ · mol⁻¹ and 3.46 · 10⁻² s⁻¹, respectively. Other activation thermodynamic parameters, entropy, ΔS (J · mol⁻¹ · K⁻¹), enthalpy, ΔH (kJ · mol⁻¹), Gibbs free energy, ΔG (kJ · mol⁻¹) and equilibrium constant, K_e were calculated at T = (283.2, 303.2, 323.2, and 343.2) K. The study was exothermic due to the decrease of entropy and was a non-spontaneous process during activation.     

Energetics of aminomethylpyrimidines: An examination of the aromaticity of nitrogen heteromonocyclic derivatives

The standard (p^o = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at the reference temperature of 298.15 K, of 2-amino-4-methylpyrimidine ((98.1 ± 1.6) kJ · mol⁻¹), 2-amino-4,6-dimethylpyrimidine ((55.9 ± 1.8) kJ · mol⁻¹) and 4-amino-2,6-dimethylpyrimidine ((60.1 ± 1.8) kJ · mol⁻¹) were calculated from the enthalpies of formation, in the crystalline phase, and enthalpies of sublimation, derived, respectively, from static bomb combustion calorimetry and Knudsen effusion technique results. In order to quantify the resonance effects arising from the substitution on the pyrimidine ring, hypothetical isodesmic reactions were used to analyze the experimental gaseous-phase enthalpies of formation. The aromaticity of benzene, pyridine, pyrimidine and the substituted pyrimidines was investigated in terms of magnetic (NICS), geometric (HOMA), electronic (Shannon aromaticity, QTAIMs ring critical point properties and HOMO–LUMO gap), reactive (hardness), vibrational (Kekulé mode) and spectroscopic (UV–Vis) properties.     

The standard molar enthalpy of sublimation ofη5-bis-pentamethylcyclopentadienyl iron measured with an electrically calibrated vacuum-drop sublimation microcalorimetric apparatus

A heat-flow Calvet microcalorimeter was adapted for the measurement of sublimation enthalpies by the vacuum-drop method, with samples of masses in the range 1 mg to 5 mg. The electrically calibrated apparatus was tested by determining the enthalpies of sublimation of benzoic acid and ferrocene, at T =  298.15 K. The obtained results, Δ_cr^gH_m^o(C₇H₆O₂)  =  (88.3  ±  0.5)kJ · mol ^− 1and Δ_cr^gH_m^o(C₁₀H₁₀Fe) =  (73.3  ±  0.1)kJ · mol ^− 1, are in excellent agreement with the corresponding values recommended in the literature. Subsequent application of the apparatus to the determination of the enthalpy of sublimation of η⁵-bis-pentamethylcyclopentadyenyl iron, at T =  298.15 K, led to Δ_cr^gH_m^o(C₂₀H₃₀Fe)  =  (96.8  ±  0.6)kJ · mol ^− 1.     

Heat capacities,third-law entropies and thermodynamic functions of the negative thermal expansion material Zn2GeO4 from T=(0 to 400) K

The molar heat capacity of Zn₂GeO₄, a material which exhibits negative thermal expansion below ambient temperatures, has been measured in the temperature range 0.5⩽(T/K)⩽400. At T=298.15 K, the standard molar heat capacity is (131.86 ± 0.26) J · K⁻¹ · mol⁻¹. Thermodynamic functions have been generated from smoothed fits of the experimental results. The standard molar entropy at T=298.15 K is (145.12 ± 0.29) J · K⁻¹ · mol⁻¹. The existence of low-energy modes is supported by the excess heat capacity in Zn₂GeO₄ compared to the sums of the constituent binary oxides.     

The vapour pressures of saturated aqueous solutions of magnesium,calcium, nickel and zinc acetates and molar enthalpies of solution of magnesium,calcium, zinc and lead acetates

Vapour pressures of water over saturated solutions of magnesium, calcium, nickel and zinc acetates were determined as a function of temperature. The vapour pressures served to evaluate the water activities, osmotic coefficients and molar enthalpies of vaporization. Molar enthalpies of solution of magnesium acetate tetrahydrate,Δ_solH_m (T =  294.71K ;m =  0.01 mol · kg ^− 1)  =  − (15.65  ±  0.97)kJ · mol ^− 1; calcium acetate,Δ_solH_m (T =  297.18K ;m =  0.01 mol · kg ^− 1)  =  − (28.15  ±  0.28)kJ · mol ^− 1; zinc acetate dihydrate,Δ_solH_m (T =  297.36K ;m =  0.01 mol · kg ^− 1)  =  − (22.49  ±  0.90)kJ · mol ^− 1and lead acetate trihydrate,Δ_solH_m (T =  297.36K ;m =  0.0086 mol · kg ^− 1)  =  (22.46  ±  0.94)kJ · mol ^− 1, were determined calorimetrically.     

Low-temperature heat capacity and standard molar enthalpy of formation of 9-fluorenemethanol (C14H12O)

Low-temperature heat capacities of the 9-fluorenemethanol (C₁₄H₁₂O) have been precisely measured with a small sample automatic adiabatic calorimeter over the temperature range between T=78 K and T=390 K. The solid–liquid phase transition of the compound has been observed to be T_fus=(376.567±0.012) K from the heat-capacity measurements. The molar enthalpy and entropy of the melting of the substance were determined to be Δ_fusH_m=(26.273±0.013) kJ · mol⁻¹ and Δ_fusS_m=(69.770±0.035) J · K⁻¹ · mol⁻¹. The experimental values of molar heat capacities in solid and liquid regions have been fitted to two polynomial equations by the least squares method. The constant-volume energy and standard molar enthalpy of combustion of the compound have been determined, Δ_cU(C₁₄H₁₂O, s)=−(7125.56 ± 4.62) kJ · mol⁻¹ and Δ_cH_m^∘(C₁₄H₁₂O, s)=−(7131.76 ± 4.62) kJ · mol⁻¹, by means of a homemade precision oxygen-bomb combustion calorimeter at T=(298.15±0.001) K. The standard molar enthalpy of formation of the compound has been derived, Δ_fH_m^∘(C₁₄H₁₂O,s)=−(92.36 ± 0.97) kJ · mol⁻¹, from the standard molar enthalpy of combustion of the compound in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.     

Heat capacities,third-law entropies and thermodynamic functions of the geometrically frustrated antiferromagnetic spinels GeCo2O4 and GeNi2O4 from T=(0 to 400) K

The molar heat capacities of GeCo₂O₄ and GeNi₂O₄, two geometrically frustrated spinels, have been measured in the temperature range from T=(0.5 to 400) K. Anomalies associated with magnetic ordering occur in the heat capacities of both compounds. The transition in GeCo₂O₄ occurs at T=20.6 K while two peaks are found in the heat capacity of GeNi₂O₄, both within the narrow temperature range between 11.4<(T/K)<12.2. Thermodynamic functions have been generated from smoothed fits of the experimental results. At T=298.15 K the standard molar heat capacities are (143.44 ± 0.14) J · K⁻¹ · mol⁻¹ for GeCo₂O₄ and (130.76 ± 0.13) J · K⁻¹ · mol⁻¹ for GeNi₂O₄. The standard molar entropies at T=298.15 K for GeCo₂O₄ and GeNi₂O₄ are (149.20 ± 0.60) J · K⁻¹ · mol⁻¹ and (131.80 ± 0.53) J · K⁻¹ · mol⁻¹ respectively. Above 100 K, the heat capacity of the cobalt compound is significantly higher than that of the nickel compound. The excess heat capacity can be reasonably modeled by the assumption of a Schottky contribution arising from the thermal excitation of electronic states associated with the CO²⁺ ion in a cubic crystal field. The splittings obtained, 230 cm⁻¹ for the four-fold-degenerate first excited state and 610 cm⁻¹ for the six-fold degenerate second excited state, are significantly lower than those observed in pure CoO.     

Standard Gibbs energy of formation of platinic acid H2Pt(OH) 6in the crystalline state

Heat capacity of platinic acid, hydrogen hexahydroxyplatinate(IV)H₂Pt(OH)₆ , was measured from T =  7 K toT =  310 K by means of adiabatic calorimetry. The standard entropy and the standard Gibbs energy of formation of platinic acid in the crystalline state were determined to be 176.5  ±  3.6 J · K ^− 1· mol ^− 1and  − 988.8  ±  3.8 kJ · mol ^− 1, respectively.     

Low-temperature thermal properties of 2,2-dimethyl-1,3-propanediol and its deuterated analogues

Heat capacities of 2,2-dimethyl-1,3-propanediol(CH₃)₂C(CH₂OH)₂ were measured in the temperature range between T =  13 K and T =  350 K using an adiabatic calorimeter. The compound underwent a first-order phase transition at T =  (314.5  ±  0.1) K. The enthalpy and the entropy of transition were (12.52  ±  0.02)kJ · mol ^− 1and (39.81  ±  0.08)J · K ^− 1· mol ^− 1, respectively. Measurement of the fusion peak by d.s.c. showed that the purity of the sample was 0.9999 mass fraction and the entropy of fusion was 9.9 J · K ^− 1· mol ^− 1. Another first-order phase transition was observed at T =  (60.4  ±  0.1) K with the associated entropy change of (2.93  ±  0.05)J · K ^− 1· mol ^− 1. Heat capacities of two deuterated samples,(CH₃)₂C(CH₂OD)₂ and(CD₃)₂C(CD₂OD)₂ , were also measured and the results were compared with those on the natural compound. Possible mechanisms of the transition have been discussed from the isotope effects on the thermodynamic quantities associated with the transition. Standard thermodynamic functions of the compounds are tabulated.     

High-temperature calorimetry of zirconia: Heat capacity and thermodynamics of the monoclinic–tetragonal phase transition

The high-temperature heat capacity of zirconia was directly measured by differential scanning calorimetry between T = (1050 and 1700) K and derived from the heat content measured by transposed temperature drop calorimetry between T = (970 and 1770) K, including the monoclinic–tetragonal (m–t) phase transition region. The enthalpy and entropy of the m–t phase transition are (5.43 ± 0.31) kJ · mol⁻¹ and (3.69 ± 0.21) J · K⁻¹ · mol⁻¹, respectively. Values of thermodynamic functions are provided from room temperature to 2000 K.     

Thermodynamic properties of Na2Ti6O13 and Na2Ti3O7: electrochemical and calorimetric determination

Standard values of Gibbs free energy, entropy, and enthalpy of Na₂Ti₆O₁₃ and Na₂Ti₃O₇ were determined by evaluating emf-measurements of thermodynamically defined solid state electrochemical cells based on a Na–β″-alumina electrolyte. The central part of the anodic half cell consisted of Na₂CO₃, while two appropriate coexisting phases of the ternary system Na–Ti–O are used as cathodic materials. The cell was placed in an atmosphere containing CO₂ and O₂. By combining the results of emf-measurements in the temperature range of 573⩽T/K⩽1023 and of adiabatic calorimetric measurements of the heat capacities in the low-temperature region 15⩽T/K⩽300, the thermodynamic data were determined for a wide temperature range of 15⩽T/K⩽1100. The standard molar enthalpy of formation and standard molar entropy at T=298.15 K as determined by emf-measurements are Δ_fH_m⁰=(−6277.9±6.5) kJ · mol⁻¹ and S_m⁰=(404.6±5.3) J · mol⁻¹ · K⁻¹ for Na₂Ti₆O₁₃ and Δ_fH_m⁰=(−3459.2±3.8) kJ · mol⁻¹ and S_m⁰=(227.8±3.7) J · mol⁻¹ · K⁻¹ for Na₂Ti₃O₇. The standard molar entropy at T=298.15 K obtained from low-temperature calorimetry is S_m⁰=399.7 J · mol⁻¹ · K⁻¹ and S_m⁰=229.4 J · mol⁻¹ · K⁻¹ for Na₂Ti₆O₁₃ and Na₂Ti₃O₇, respectively. The phase widths with respect to Na₂O content were studied by using a Na₂O-titration technique.     

Excess molar volumes of binary mixtures of 2,2,2-trifluoroethanol with water,or acetone,or 1,4-difluorobenzene,or 4-fluorotoluene,or α,α,α, trifluorotoluene or 1-alcohols at a temperature of 298.15 K and pressure of 101 kPa

Excess molar volumes V_m^E of binary mixtures of 2,2,2-trifluoroethanol with water, or acetone, or methanol, or ethanol, or 1-alcholos, or 1,4-difluorobenzene, or 4-fluorotoluene or α,α,α-trifluorotoluene were measured in a vibrating tube densimeter at temperature 298.15 K and pressure of 101 kPa. The V_m^E extrema are: 1.540 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + 1-heptanol); 1.452 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + 1-hexanol); 1.238 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + 1-butanol); 0.821 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + 4-fluorotoluene); 0.817 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + ethanol); 0.647 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + methanol); 0.618 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + acetone); 0.605 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + α,α,α-trifluorotoluene); 0.485 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + 1,4-difluorobenzene); and −0.656 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + water). The limiting excess partial molar volumes are estimated.     

Determination of the standard enthalpy of formation of paratungstate A ion

Enthalpy changes for the reaction of HCl(aq) withNa₂WO₄ (aq) were measured at T =  298.15 K in a HT-1000 calorimeter. The standard enthalpy of reaction for the formation ofW₇O₂₄^6 −  (aq) was calculated on the basis of the experimental results, Δ_rH_m^o(298.15K )  =  − (320.7  ±  1.0)kJ · mol ^− 1. Combining this with the values from the literature led to the standard enthalpy of formation of W₇O₂₄^6 − (aq),Δ_fH_m^o (298.15 K)  =  − 6689.8 kJ · mol ^− 1.     

An isoperibol micro-bomb calorimeter for measurement of the enthalpy of combustion of organic compounds. Application to the study of succinic acid and acetanilide

A micro static-bomb combustion calorimeter, developed from a 1107 Parr semi-micro bomb, has been provided with a new micro-bomb and calorimetric bucket. In the best conditions of operation, the energy equivalent of this calorimetric arrangement is just ε(calor)=(731.82 ± 0.22) J · K⁻¹, which means an uncertainty of 0.03 per cent for the calibration with benzoic acid NIST 39j. This combustion calorimeter has been used in the measurement of the enthalpy of combustion of the succinic acid and acetanilide, giving −(1489.3 ± 1.6) kJ · mol⁻¹ and −(4222.5 ± 1.1) kJ · mol⁻¹, respectively, for these substances.