Standard thermodynamic properties of nitrobenzene in the ideal gas state

The standard enthalpy of formation of gaseous nitrobenzene was calculated by the G3X nonempirical quantum-mechanical method. The value obtained (56 kJ/mol) was noticeably lower than the experimental enthalpy, which casts doubt on the accuracy of measurements. The thermodynamic functions (C° _p , S°, ?[G° ? H°(0)]/T, H° ? H°(0), Δ_f H°, and Δ_f G°) of nitrobenzene in the ideal gas state were calculated by the statistical thermodynamics method over the temperature range 150–1500 K (the molecular constants, including the structural parameters, vibrational frequencies, and internal rotation potential used in the calculations were taken from the literature or estimated by the quantum-mechanical method).     

Monte Carlo calculation of the thermodynamic properties of water

The Monte Carlo method and parallel computing are used to calculate the thermodynamic properties of water (density, heat capacity, compressibility, thermal expansion coefficient, and static dielectric constant) in a wide range of temperatures (from 70 K to 530 K) at constant (atmospheric) pressure. Four groups of computational experiments are carried out, each for its own model of the water molecule: TIP3P (Jorgensen et al., 1983), SPC/E (Berendsen et al., 1987), TIP4P/2005 (Abascal&Vega, 2005), and TIP5P-E (Rick, 2004). An additional calculation based on the replica exchange method is conducted for the TIP4P/2005 model. A comparison of the calculated properties of water with experimental data suggests that the TIP4P/2005 model can provide highly realistic computer simulation results for water and aqueous solutions.     

Catalytic properties of copper chromite ferrites in water gas shift reaction and hydrogen oxidation

The catalytic properties of a series of copper chromite ferrite samples with the composition CuCr_2–xFe_xO₄ (where x = 0–2) and a spinel-type structure in reactions with reducing (water gas shift reaction, WGSR) and oxidizing (the oxidation of hydrogen) reaction atmospheres were studied. The samples were obtained by the thermal decomposition of mixed hydroxo compounds. The distribution of Cu²⁺ ions in the tetrahedral and octahedral crystallographic positions of spinel, which depends on the Cr³⁺/Fe³⁺ ratio, affects the apparent activation energy (E_a) in both of the reactions. In WGSR, E_a is ～33 kJ/mol for CuCr₂O₄, in which Cu²⁺ ions mainly occupy tetrahedral positions, whereas E_a ≈ 100 kJ/mol for CuFe₂O₄, in which Cu²⁺ ions mainly occupy octahedral positions. In the reaction of hydrogen oxidation, E_a is ～71 kJ/mol for CuCr₂O₄ or ～42 kJ/mol for CuFe₂O₄. The value of E_a for the mixed chromite ferrites changes with the replacement of chromium ions by iron ions and, hence, with a ratio between the amounts of copper ions in the tetrahedral and octahedral oxygen positions of spinel.     

Influence of maltodextrins with different dextrose equivalent on the thermodynamic properties of legumin in a bulk and at the air–water interface

This paper presents the influence of the potato maltodextrins with different dextrose equivalent (DE 2, 6 and 10) on the legumin thermodynamic properties in the bulk aqueous medium and at the air–water interface both in the simple mixed solutions and under the covalent complex (conjugate) formation (by the Maillard reaction), at pH 7.0 and ionic strength of 0.05 mol dm⁻³. The weak net attractive interaction between legumin and maltodextrin has been found in an aqueous medium by both the light scattering and the mixing calorimetry methods. On the basis of both the mixing and differential scanning calorimetry data a hydrogen bonding is supposed to be fundamental for this interaction. It was found that these attractive interactions produced an increase in the protein hydrophilicity and consequently a decrease in the protein surface activity. The effect was more pronounced for the maltodextrin with the largest dextrose equivalent (DE 10). The covalent complexation between legumin and maltodextrin induced the change of the fine hydrophobic–hydrophilic balance in the protein globule due to both addition of the hydrophilicity of the covalently attached polysaccharide and the partial protein unfolding as a result of the such kind of attachment. The combined data of tensiometry, light scattering, mixing and differential scanning calorimetry demonstrated the importance of the maltodextrin polymerization (DE) in controlling both the protein hydrophilicity (thermodynamic affinity for the aqueous phase) and surface activity.     

The effect of sucrose on the thermodynamic properties of ovalbumin and sodium caseinate in bulk solution and at air–water interface

This paper presents a study of the effect of sucrose on the molecular parameters and thermodynamic properties in a bulk aqueous medium and at the air–water interface for two proteins differing both in nature and structure, that is Na-caseinate and ovalbumin. To get more insight into the molecular nature of the effect of sucrose, mixing calorimetry, light scattering and tensiometry measurements have been made under different pHs (7.0 and 5.5) and temperatures (20–55°C) at an ionic strength of 0.005 mol dm⁻³. Combined temperature dependencies of light scattering and mixing calorimetry testify to hydrogen bonding (sucrose-protein and/or sucrose-water) as being the primary basis of the effect of sucrose on the molecular and thermodynamic properties of the proteins in the bulk and at interface of an aqueous medium. At pH 7.0, in the case of ovalbumin, the interaction with sucrose causes an increase in the protein hydrophilicity in the bulk aqueous medium followed by a decrease in the protein surface activity, whilst for Na-caseinate, there is an increase in the protein hydrophobicity due to Na-caseinate micelle dissociation and, consequently, to an increase in the protein surface activity. Lowering the pH to 5.5, accompanied by a strengthening of the competition between less charged proteins and sucrose for water molecules, induces a rise in the protein hydrophobic aggregation in the bulk. The special features of the latter process are probably mainly responsible for the changes in the surface activity of the proteins under influence of sucrose at pH 5.5.     

On the formation of hydrogen gas on copper in anoxic water

Hydrogen gas has been detected in a closed system containing copper and pure anoxic water [P. Szakalos, G. Hultquist, and G. Wikmark, Electrochem. Solid-State Lett. 10, C63 (2007) and G. Hultquist, P. Szakalos, M. Graham, A. Belonoshko, G. Sproule, L. Grasjo, P. Dorogokupets, B. Danilov, T. Aastrup, G. Wikmark, G. Chuah, J. Eriksson, and A. Rosengren, Catal. Lett. 132, 311 (2009)]. Although bulk corrosion into any of the known phases of copper is thermodynamically forbidden, the present paper shows how surface reactions lead to the formation of hydrogen gas in limited amounts. While water cleavage on copper has been reported and investigated before, formation of molecular hydrogen at a single-crystal Cu[100] surface is here explored using density functional theory and transition state theory. It is found that although solvent catalysis seems possible, the fastest route to the formation of molecular hydrogen is the direct combination of hydrogen atoms on the copper surface. The activation free energy (ΔG(s)(?)(f)) of hydrogen formation in condensed phase is 0.70 eV, which corresponds to a rate constant of 10 s(-1) at 298.15 K, i.e., a relatively rapid process. It is estimated that at least 2.4 ng hydrogen gas could form per cm(2) on a perfect copper surface.     

X-ray absorption spectroscopy study of the hydrogen bond network in the bulk water of aqueous solutions

We utilized X-ray absorption spectroscopy (XAS) and X-ray Raman scattering (XRS) in order to study the ion solvation effect on the bulk hydrogen bonding structure of water. The fine structures in the X-ray absorption spectra are sensitive to the local environment of the probed water molecule related to the hydrogen bond length and angles. By varying the concentration of ions, we can distinguish between contributions from water in the bulk and in the first solvation sphere. We show that the hydrogen bond network in bulk water, in terms of forming and breaking hydrogen bonds as detected by XAS/XRS, remains unchanged, and only the water molecules in the close vicinity to the ions are affected.     

Vapor-pressure osmometry and inverse gas chromatography in the analysis of thermodynamic properties of polymer solutions

The primary objective of this work is to check the utility of vapor-pressure osmometry as an experimental technique in obtaining thermodynamic data on polymer/solvent systems. The second objective is to obtain experimental values for the exchange energy parameters ΔP, X, and ζ of the theory of Sanchez and Lacombe. With respect to the first objective, solvent activities of polyiso-butylene/benzene mixtures have been measured at several concentrations up to 600 g/kg of the solvent and at two temperatures. From the activities, it is possible to determine free energies, entropies, and enthalpies and their concentration dependence. Satisfactory agreement has been found between the results obtained and data provided by other techniques such as membrane osmometry and the Cahn electrobalance. These and other data obtained by inverse gas chromatography for the same mixture in the range 35–200°C have been used in calculating the exchange energy parameter of the lattice fluid theory at different concentrations and temperatures.     

Nonempirical studies of the molecular properties and thermodynamic functions of urea in the ideal gas state

Quantum-chemical calculations were performed for the equilibrium structure of isolated urea molecules using the 6-311++G** basis set and second-order M?ller-Plesset perturbation theory, density functional theory, and the coupled cluster method with the local inclusion of electron correlation. The results were used to perform statistical calculations of the standard thermodynamic functions of urea in the ideal gas state taking into account anharmonicity of normal vibrations. The contributions of dimerization and isomerization of urea molecules in the vapor phase were determined. The recommended values were compared with the available experimental data and the results of preceding calculations. Original Russian Text ? A.V. Kuznetsov, A.V. Stolyarov, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 2, pp. 339–345.     

Interaction of gas phase atomic hydrogen with Pt(111):Direct evidence for the formation of bulk hydrogen species

Employing hot tungsten filament to thermal dissociate molecular hydrogen,we generated gas phase atomic hydrogen under ultra-high vacuum(UHV)conditions and investigated its interaction with Pt(111) surface.Thermal desorption spectroscopy(TDS)results demonstrate that adsorption of molecular hy- drogen on Pt(111)forms surface Had species whereas adsorption of atomic hydrogen forms not only surface Had species but also bulk Had species.Bulk Had species is more thermal-unstable than surface Had species on Pt(111),suggesting that bulk Had species is more energetic.This kind of weakly- adsorbed bulk Had species might be the active hydrogen species in the Pt-catalyzed hydrogenation reactions.     

Investigation of thermodynamic properties of hyperbranched aliphatic polyesters by inverse gas chromatography

Thermodynamic properties of a series of commercial hyperbranched aliphatic polyesters (Boltorn^® H20, H30 and H40) were examined for the first time by inverse gas chromatography (IGC) using 13 different solvents at infinite dilution as probes. Retention data of probes were utilized for an extensive characterization of polymers, which includes the determination of the Flory–Huggins interaction parameter, the weight fraction activity coefficient as well as the total and partial solubility parameters. Analysis of the results indicated that the total and partial solubility parameters decrease with increase of temperature. Furthermore, upon increase of the molecular weight, while the hydrogen bonding component decreases, no influence on the total solubility parameter is noticed within the experimental error margins. Results from the present study while providing new insight to the thermodynamic characteristics of the examined systems, they are also expected to reflect more general aspects of the behavior of hyperbranched polymers bearing similar end-groups.     

Structural and thermodynamic properties of different phases of supercooled liquid water

Computer simulation results are reported for a realistic polarizable potential model of water in the supercooled region. Three states, corresponding to the low density amorphous ice, high density amorphous ice, and very high density amorphous ice phases are chosen for the analyses. These states are located close to the liquid-liquid coexistence lines already shown to exist for the considered model. Thermodynamic and structural quantities are calculated, in order to characterize the properties of the three phases. The results point out the increasing relevance of the interstitial neighbors, which clearly appear in going from the low to the very high density amorphous phases. The interstitial neighbors are found to be, at the same time, also distant neighbors along the hydrogen bonded network of the molecules. The role of these interstitial neighbors has been discussed in connection with the interpretation of recent neutron scattering measurements. The structural properties of the systems are characterized by looking at the angular distribution of neighboring molecules, volume and face area distribution of the Voronoi polyhedra, and order parameters. The cumulative analysis of all the corresponding results confirms the assumption that a close similarity between the structural arrangement of molecules in the three explored amorphous phases and that of the ice polymorphs I(h), III, and VI exists.     

Perfect gas thermodynamic properties of methanal,ethanal and their deuterated species

Employing recent and reliable selected molecular, spectroscopic, and thermal constants, the perfect gas thermodynamic properties [H⁰  H⁰₀, (G⁰  H⁰₀)/T, S⁰, C⁰_p, ΔH⁰_f, and ΔG⁰_f], for methanal (formaldehyde), methanal-d₁, methanal-d₂, ethanal (acetaldehyde), ethanal-d₁, and ethanal-d₄ were evaluated over the temperature range from 0 to 1500 K and 1 atm by statistical mechanical methods using rigid-rotor and harmonic-oscillator approximations. The internal rotation contributions of -CH₃ and -CD₃ rotors to the thermodynamic properties were computed based on internal rotation partition functions formed by summation of calculated internal rotation energy levels. The results compare well with available experimental data.     

Ideal gas thermodynamic properties of benzenediols: Pyrocatechol, resorcinol and hydroquinone

The vibrational fundamentals have been selected using the available literature data. −271.96, −274.89 and −261.71 kJ mole⁻¹ are selected for the enthalpies of formation (g, 298.15 K) for pyrocatechol, resorcinol and hydroquinone, respectively. The ideal gas thermodynamic properties are obtained assuming one, three and two rotational isomers for 1,2-, 1,3-, and 1,4-benzenediol, respectively.     

Accurate measurements of thermodynamic properties of solutes in ionic liquids using inverse gas chromatography

Activity coefficients at infinite dilution of 29 organic compounds in two room temperature ionic liquids were determined using inverse gas chromatography. The measurements were carried out at different temperatures between 323.15 and 343.15K. To establish the influence of concurrent retention mechanisms on the accuracy of activity coefficients at infinite dilution for 1-butyl-3-methylimidazolium octyl sulfate and 1-ethyl-3-methylimidazolium tosylate, phase loading studies of the net retention volume per gram of packing as a function of the percent phase loading were used. It is shown that most of the solutes are retained largely by partition with a small contribution from adsorption on 1-butyl-3-methylimidazolium octyl sulfate and that the n-alkanes are retained predominantly by interfacial adsorption on 1-ethyl-3-methylimidazolium tosylate.     

On the thermodynamic stability of hydrogen clathrate hydrates

The cage occupancy of hydrogen clathrate hydrate has been examined by grand canonical Monte Carlo (GCMC) simulations for wide ranges of temperature and pressure. The simulations are carried out with a fixed number of water molecules and a fixed chemical potential of the guest species so that hydrogen molecules can be created or annihilated in the clathrate. Two types of the GCMC simulations are performed; in one the volume of the clathrate is fixed and in the other it is allowed to adjust itself under a preset pressure so as to take account of compression by a hydrostatic pressure and expansion due to multiple cage occupancy. It is found that the smaller cage in structure II is practically incapable of accommodating more than a single guest molecule even at pressures as high as 500 MPa, which agrees with the recent experimental investigations. The larger cage is found to encapsulate at most 4 hydrogen molecules, but its occupancy is dependent significantly on the pressure of hydrogen.