Thermochemical investigations of the systems KCl−KBr−H2O,K2SO4−(NH4)2SO4−H2O and KNO3−NH4NO3−H2O at 298.15 K

For the equilibrium solid phases occurring in the systems: KCl?KBr?H₂O, K₂SO₄?(NH₄)₂SO₄?H₂O and KNO₃?NH₄NO₃?H₂O, the concentration dependencies of differential solution enthalpies, Δ_sol H ₂ for several crystallization paths, were measured. The limiting differential solution enthalpies, Δ_sol H ₂ ⁰ , were determined by extrapolation of the above dependencies to the ionic strength,I _m ⁰ , corresponding to the appropriate binary solutions. For KCl?KBr?H₂O system only, the clear dependence between Δ_sol H ₂ ⁰ andI _m ⁰ values was found and discussed.     

A theoretical study of the H2SO4+H2O → HSO4 −+H3O+ reaction at the surface of aqueous aerosols

The surface region of sulfate aerosols (supercooled aqueous concentrated sulfuric acid solutions) is the likely site of a number of important heterogeneous reactions in various locations in the atmosphere, but the surface region ionic composition is not known. As a first step in exploring this issue, the first acid ionization reaction for sulfuric acid, H₂SO₄ + H₂O HSO₄^– + H₃O⁺, is studied via electronic structure calculations at the Hartree–Fock level on an H₂SO₄ molecule embedded in the surface region of a cluster containing 33 water molecules. An initial H₂SO₄ configuration is selected which could produce H₃O⁺ readily available for heterogeneous reactions, but which involves reduced solvation and is consistent with no dangling OH bonds for H₂SO₄. It is found that at 0 K and with zero-point energy included, the proton transfer is endothermic by 3.4 kcal/mol. This result is discussed in the context of reactions on sulfate aerosol surfaces and, further, more complex calculations.Contribution to the Jacopo Tomasi Honorary Issue     

Thermal magnetic investigation of the decomposition of NixMn1−xC2O4·2H2O

The systems Ni_xMn_1?xC₂O₄·2H₂O (x = 0.11, 0.34) are characterized by XRD, SEM, TG/DTA, EGA-MS and magnetic measurements. The last confirmed that the studied samples are real solid solutions. The SEM reveals that the morphology depends on both the excess of C₂O₄^2? and the initial ratio Ni/Mn. The thermal magnetic investigations (in situ) show that: (i) the presence of Ni in Ni_xMn_1?xC₂O₄·2H₂O leads to decreasing in the decomposition temperature in regard to that of the manganese oxalate; (ii) upon increasing the Ni content the temperature of decomposition (in air) is growing up; (iii) the presence of Ni stabilizes the manganese with respect to oxidation, in spite of the occurring process of decomposition.     

Temperature dependence of the substrate selectivity in the hydroxylation of alkylbenzenes in the H2O2−H2SO4 system

The substrate selectivity in the hydroxylation of methylbenzenes in the H₂O₂−H₂SO₄ (70 wt.%) system was studied at 15–55 °C. The activation entropy correlates with the basicity of the arenes, while the substrate selectivity and activation enthalpy correspond both with the basicity and ionization potentials of ArH. We concluded that the structure of the reaction transition state is intermediate between a charge transfer complex and σ-complex. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 39–43, January–February, 1999.     

Study of the process of the hydroxo complexes formation in the Al3+-Hg2+-NO 3 − -H2O and Al3+-Cd2+-NO 3 − -H2O systems

Russian Journal of Applied Chemistry - The process of hydrolysis in the Al3+-Cd2+-NO 3 ? -H2O and Al3+-Hg2+-NO 3 ? -H2O systems is studie by the methods of pH-metric titration and...     

Comment on the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures

In a recent paper (Radiation Physics and Chemistry, 2005, vol. 74, pp. 210) it was suggested that the anomalous increase of molecular hydrogen radiolysis yields observed in high-temperature water is explained by a high activation energy for the reaction H+H₂O→H₂+OH. In this comment we present thermodynamic arguments to demonstrate that this reaction cannot be as fast as suggested. A best estimate for the rate constant is 2.2×10³ M⁻¹ s⁻¹ at 300 °C. Central to this argument is an estimate of the OH radical hydration free energy vs. temperature, ΔG_hyd(OH)=0.0278t−18.4 kJ/mole (t in °C, equidensity standard states), which is based on analogy with the hydration free energy of water and of hydrogen peroxide.     

Kinetics of H2S destruction in the radiolysis of CH4−H2S gas mixtures

The kinetics of H₂S destruction in the radiolysis of CH₄–H₂S and CH₄–H₂S–O₂ mixtures has been studied. It has been shown that G(–H₂S) depends on amounts of hydrogen sulfide and the presence of oxygen in the starting mixture and is within the range of 5–13 mol/100 eV. G(H₂) decreases with the increases of O₂ content and amounts to the constant value of 2.     

Determination of the protonation state of [H3PW11O39]4− and the stability constant of [Ag(H2O)(H3PW11O39)]3− in aqueous solution

By employing elemental analysis, ³¹P NMR, pH, and conductivity measurements, the protonated state of lacunary heteropolyoxotungstophosphates in aqueous solution, {PW₁₁O₃₉}, is determined to be [H₃PW₁₁O₃₉]^4?. Using it as ligand, a complex of [Ag(H₂O)(H₃PW₁₁O₃₉)]^3? is formed. An electrochemical cell is designed as follows: (?) Hg, Hg₂Cl₂ [Ag(H₂O)(H₃PW₁₁O₃₉)]^3? (aq) | Ag(s) (+) (salt bridge is saturated KNO₃ solution). By measuring the electromotive force of the cell, the stability constant of [Ag(H₂O)(H₃PW₁₁O₃₉)]^3? in aqueous solution is determined to be 4.34 × 10³ (25 °C).     

Transport numbers of H+ and O2- in the electrochemical system (H2 + H2O),Me/BaCe0.9Nd0.1O3-α/Me,(H2 + H2O)

In the temperature range 873–1123 K, transport numbers of oxygen ions and protons are determined in the system (H₂ + H₂O), Me/BaCe_0.9Nd_0.1O_3-α/Me,(H₂ + H₂O), where Me = Ag, Au, Pt, Ni, by the emf and current methods. The determined transport numbers are independent of the determination method, the electrode material, the current direction (anodic and cathodic polarization of the electrode), polarizability of electrodes, and the partial water (hydrogen) pressure in the gas phase. This unambiguously suggests that the transport numbers refer to the solid electrolyte, and not the electrochemical system as a whole. It also follows that partial currents of the hydrogen ionization and the oxygen ion discharge are determined by the transport numbers of protons and oxygen ions in the electrolyte. At a constant temperature, their ratio is affected by neither the electrode potential nor the gas phase composition, i.e., both electrode reactions have a common limiting step (or steps). Deceased.     

Reply to comment on the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures

In reply to “Comment on the possible role of reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures” (Bartels, 2009 Comment on the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) we present an alternative thermodynamic estimation of the reaction rate constant k. Based on the non-symmetric standard state convention we have calculated that the Gibbs energy of reaction Δ_rG=57.26 kJ mol^?1 and the reaction rate constant k=7.23×10^?5 M^?1 s^?1 at ambient temperature. Re-analysis of the thermodynamic estimation (Bartels, 2009 Comment on the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) showed that the upper limit for the rate constant at 573 K is k=1.75×10⁴ M^?1 s^?1 compared to the value predicted by the diffusion-kinetic modelling (3.18±1.25)×10⁴ M^?1 s^?1 (Swiatla-Wojcik, D., Buxton, G.V., 2005. On the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 74(3–4), 210–219). The presented thermodynamic evaluation of k(573) is based on the assumption that k can be calculated from Δ_rG and the rate constant of the reverse reaction which, as discussed, are both uncertain at high temperatures.     

The Influence of Weakly Coordinating Cations on the O−H⋅⋅⋅O− Hydrogen Bond of Silanol-Silanolate Anions

The reaction of a saline phosphazenium hydroxide hydrate with siloxanes led to a novel kind of silanol-silanolate anions. The weakly coordinating behavior of the cation renders the formation of silanol-silanolate hydrogen bonds possible, which otherwise suffer from detrimental silanolate–oxygen cation interactions. We investigated the influence of various weakly coordinating cations on silanol-silanolate motifs, particularly with regard to different cation sizes. While large cations favor the formation of intramolecular hydrogen bonds resulting in cyclic structures, the less bulky tetramethyl ammonium cation encourages the formation of polyanionic silanol-silanolate chains in the solid state.     

An analysis of the vibrational frequencies and amplitudes of the H5O+2 ion in H4SiW12O40·6H2O (TSA·6H2O) and H3PW12O40·6H2O (TPA·6H2O)

The infrared, Raman and inelastic neutron scattering (INS) spectra of TSA·6H₂O and TPA·6H₂O are in agreement with those expected for the presence of H₅O⁺₂ ions. Force fields for different assignment schemes are compared with the observed vibrational frequencies and the INS spectral profile. All but two schemes are eliminated. Whilst low-resolution INS spectroscopy cannot distinguish between these two schemes, the orientations of the vibrational ellipsoids for one scheme are in better agreement with those reported from low-temperature crystallographic studies of the H₅O⁺₂ ion.     

Application of the Ru(bipy)2(dpp)2+ / C2O4 2− electrochemiluminescence reaction to the determination of phenol

The electrochemiluminescence (ECL) of the ruthenium di(2,2′-bipyridine)- (4,7-diphenyl-1,10-phenanthroline) complex (Ru-bipy-dpp) produced on a glassy carbon electrode was studied by cyclic voltammetry. The anodic oxidation of Ru-bipy-dpp produces ECL in the presence of oxalate in oxygen-free aqueous solutions. Threefold ECL efficiencies were obtained for Ru-bipy-dpp relative to Ru(bipy)₃ as a standard. The ECL of Ru-bipy-dpp is quenched by both oxygen and phenol. The luminescence intensity was proportional to the concentration of phenol in the range of 5–100 μM. At a phenol concentration of 100 μM, the ECL of Ru-bipy-dpp peaking at 597 nm was completely quenched. Correspondence: Dan Xiao, College of Chemistry and Chemical Engineering, Sichuan University, Chengdu 610065, P.R. China     

S−H…O and O−H…O Hydrogen Bonds-Comparison of Dimers of Thiocarboxylic and Carboxylic Acids

ωB97-XD/aug-cc-pVTZ calculations were performed on dimers of selected thiocarboxylic acids and on analogous carboxylic acids. The sample of calculated thiocarboxylic acids is an extension of the Cambridge Structural Database search that contains only a few such structures. The Natural Bond Orbital (NBO) method, Symmetry-Adapted Perturbation Theory (SAPT) approach, Non-Covalent Interaction (NCI) method and Quantum Theory of Atoms in Molecules (QTAIM) were applied additionally to analyse interactions in dimers of thiocarboxylic and carboxylic acids. The insights into crystal structures as well as into results of calculations show that the formation of S−H…O hydrogen bonds between molecules of thiocarboxylic acids is steered by the same mechanisms as the formation of much stronger O−H…O hydrogen bonds in carboxylic acids. The intramolecular O−H…O and C−H…S hydrogen bonds occurring in few considered structures are also analysed.     

Determination of the Rate Constants of the Reactions Cr + O2 + M → CrO2 + M and Cr + O2 → CrO + O

Kinetics and Catalysis - The rate constants of the interactions of chromium atoms with molecular oxygen through recombination Cr + O2 + M → CrO2 + M (I) and exchange Cr + O2 → CrO + O...     

The influence of the temperature on the liquid–liquid equlibria of the mixture limonene + ethanol + H2O

In this work, experimental liquid–liquid equilibria (LLE) of the limonene + ethanol + water system are presented. The LLE of this system has been measured at 293.15, 303.15, 313.15 and 323.15 K. The equilibrium data presented are correlated using NRTL and UNIQUAC equations. Finally, the reliability of these models is tested by comparison with experimental results.