Thermodynamic Properties of Aqueous Solution of 2-Isopropoxyethanol at 25°C

Excess enthalpy, excess isobaric heat capacity, density, and speed of sound for aqueous 2-isopropoxyethanol solutions were measured at 25°C. The density was also measured at 20°C. The excess enthalpy was –800 J-mol^–1 at the minimum (mole fraction alcohol, x = 0.2), showing that the hydrogen bonds formed between unlike molecules are stronger than those in both pure liquid states. The excess volume also was large and negative, more than –1.2 cm³-mol^–1 at the minimum (x = 0.35). Excess isentropic and isothermal compressibilities are extremely negative. These results suggest that breaking the hydrogen bond network in water and forming the stronger hydrogen bonds between unlike molecules reduces the volume of the solution and makes the solution less compressible. The excess isobaric heat capacity is positive and large, up to 10 J-K^–1-mol^–1 and shows anomalous behavior in the neighborhood of x = 0.15.     

Heats of chemisorption ofn-Aliphatic alcohols on α-Al2O3 at 25–200°C

A differential microcalorimeter (E. Calvet) was used to study the processes of adsorption of five aliphatic alcohols (C₁-C₅) on α-Al₂O₃ at 25, 50, 100, 150 and 200°C. In particular, the importance of the thermokinetic study of the chemisorption of such alcohols at different experimental temperatures was demonstrated, with regard to the variations in the thermokinetic parameters (t_max, t_1/2 and t₀) and the evolution of the alcohol vapor pressure on the adsorbent during the adsorption process. It was concluded that:

1. all the heat emission peaks of alcohol adsorption have the same rounded shape at 25°C;
2. on passing from methanol to 1-pentanol, the area of the adsorption peaks increases as the chain length or molecular weight increases;
3. on passing from 25 to 200°C, the shape of the adsorption peaks becomes more pointed.

     

Effect of pressure on the solubility of naphthalene in water at 25°C

Solubility of naphthalene in water was measured at 25°C and pressures up to 200 MPa. The solubility decreased with increasing pressure. From the pressure coefficient of the solubility, the volume change V accompanying the dissolution was estimated as 13.8±0.4 cm ³ -mol ^–1 . Further we estimated the volume change V _CH accompanying hydrophobic hydration as –0.1±0.6 cm ³ -mol ^–1 using the V value, the molar volume of crystalline naphthalene, and the partial molar volume of naphthalene in n-heptane. This V _CH is much larger (i.e., less negative) than that for hydrophobic hydration of alkyl-chain compounds and suggests that the hydration structure of naphthalene differs from that of alkyl-chain compounds.     

Phase Diagrams of Fullerenol-d–LaCl3–H2O and Fullerenol-d–GdCl3–H2O Systems at 25°С

Russian Journal of Physical Chemistry A - Isothermal phase diagrams of ternary systems fullerenol-d–LaCl3–H2O and fullerenol-d–GdCl3–H2O at 25°C are studied via...     

Solubility Diagram of a Fullerenol-d-NaCl-H2O System at 25°C

Solubility in a ternary fullerenol-d-NaCl-H₂O system is studied at 25°C with the use of isothermal saturation. It is established that the solubility diagram is composed of two branches that are responsible for the crystallization of fullerenol-d crystallohydrate and anhydrous sodium chloride, and it contains one invariant eutonic-type point that corresponds to cosaturation by the above two solid phases. The so-called salting-out effect was observed on the branch of the crystallization of fullerenol-d, while salting in was observed on the branch of the crystallization of sodium chloride.     

Isothermal Vapor–Liquid Equilibria for the Ternary System 2-Propanol + Tetrahydrofuran + 1-Chlorobutane at 25°C

Isothermal vapor–liquid equilibria (VLE) for mixtures containing 2-propanol + tetrahydrofuran + 1-chlorobutane have been measured using a modified version of a Boublik–Benson still at 25°C. A test of thermodynamic consistency, like the McDermott–Ellis method was applied to the activity coefficients. Excess molar Gibbs free energies were calculated over the entire range composition. Different expressions existing in the literature were used to predict activity coefficients.     

Spinodal Curve for the System Water + 1-Pentanol + 1-Propanol at 25 °C

The liquid–liquid equilibrium data at 25 °C of the system water–1-pentanol–1-propanol, that present a I type solubility gap, have been used to calculate the spinodal curve of this system through the use of the Wheeler–Widom model. As in the case of the water–chloroform–acetic acid system, analyzed with the same model in the past, a local fitting method has been necessary. A procedure based on the experimental position of the plait point was used to obtain the single spinodal points. The relative positions of binodal and spinodal curves indicate the presence of a large metastable area in the alcoholic-rich region.     

Hygrometric Determination of the Water Activities of the Aqueous Solutions of the Mixed Electrolyte NaCl–CaCl2–H2O at 25°C

The mixture {yNaCl + (1 – y)CaCl₂}(aq) has been studied with the hygrometric method at the temperature 25°C. The water activities were measured at total molalities from 0.25 mol-kg^–1 to near saturation for different ionic-strength fractions y of NaCl with y = 0.33, 0.50, and 0.67. The obtained data allow the calculation of osmotic coefficients. The experimental results are compared with the predictions of the Zdanovskii–Stokes–Robinson (ZSR), Kusik and Meissner (KM), Robinson and Stokes (RS), Lietzke and Stoughton (LS II), Reilly–Wood–Robinson (RWR), and Pitzer models. From the measured osmotic coefficients, the Pitzer ionic mixing parameters _{Na Ca} and _{Na Ca} Cl are determined and are used to predict the solute activity coefficients in the mixtures. The excess Gibbs energy is also determined. These results are compared with those given in the literature.     

Thermodynamic properties of binary mixtures: Hexamethylphosphoric triamide + a polar liquid at 25°C

Excess enthalpies H _m ^E excess isobaric heat capacities C _p,m ^E , densities, and speeds of sound of hexamethylphosphoric triamide (HMPA)+acetonitrile (AN), + N,N-dimethylformamide (DMF), and + dimethylsulfoxide (DMSO) were measured at 25degrC. H _m ^E =–1200 J-mol^–1 for HMPA + AN, –180 J-mol^–1 for HMPA + DMF, and 75 J-mol^–1 for HMPA + DMSO C _p,m ^E is positive and considerably larger than C _v,m ^E . V _m ^E for HMPA + DMSO was small and changed sign from negative to positive around HMPA mole fraction x=0.6. V _m ^E for the other two mixtures were negative. The excess compressibilities, K _m ^E for the other two mixtures were negative. The excess compressibilities, K _S ^E and K _T ^E were similar to V _m ^E Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30-June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

A new determination of the structure of water at 25°C

The results of a new neutron diffraction experiment to measure the structure of water are presented. The data, measured at the McMaster Nuclear Reactor, are of a high quality and are analysed to yield the hydrogen-hydrogen pair correlation function using a subtraction procedure which has been used in previous experiments of this kind. This procedure circumvents the necessity of applying inelasticity corrections. The results are in good agreement with earlier work and serve to establish the general correctness of the subtraction procedure when used to determine hydrogen correlations. The data are further analysed to yield separate oxygen-hydrogen and oxygen-oxygen partial structure factors for liquid water. For the second part of the analysis an effective mass model of the dynamic scattering law is used, with the model parameter, the effective mass of the scattering particle, chosen by a least-squares fit to the measured differential cross sections. The final pair correlation functions are obtained using a maximum entropy analysis of the structure functions.     

Thermodynamic properties of the system MgSO4–MnSO4–H2O at 298.15 K

The mixed aqueous electrolyte system magnesium and manganese sulfate has been studied with the hygrometric method at the temperature 298.15 K. The relative humidity of this system is measured at total molalities from 0.2 mol kg⁻¹ to about saturation of one of the solutes for different ionic-strength fractions y of MgSO₄ with y=0.2, 0.5 and 0.8. The obtained data allow the deduction of new thermodynamic parameters. The experimental results are compared with the predictions of ZSR rule. From these measurements, the new Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture. The obtained results are used to calculate the excess Gibbs energy at total molalities for different ionic-strength fractions y of MgSO₄.     

Molecular interactions in aqueous solutions of polyborates at different acidity based on the Raman spectroscopy data at 25°C

Investigation of aqueous solutions of polyborates LiB(OH)₄, Li₂B₄O₅(OH)₄, and LiB₅O₆(OH)₄ at different acidity has been performed by Raman spectroscopy at 25°C. The geometries and Raman vibrational frequencies of H₃BO₃ in aqueous phase were calculated at different basis sets, and verified the veracity. The calculated characteristic Raman shifts of B(OH)₃, B(OH)₄ ^?, B₃O₃(OH)₄ ^?, B₃O₃(OH)₅ ^2?, B₄O₅(OH)₄ ^2?, and B₅O₆(OH)₄ ^? were assigned to 880.0, 735.33, 599.06, 740.16, 551.67, and 521.04 cm^?1, respectively. Assignments of the bands were tentatively ascribed by comparing the calculated Raman spectrum. The chemical species distribution and the relevant molecular interaction mechanisms in the polyborates solutions were suggested.     

Apparent Molar Volumes and Adiabatic Compressibilities of Crown Ethers and Glymes in H2O and D2O at 25°C

The apparent molar volumes and adiabatic compressibilities of 18-Crown-6, 15-Crown-5, 12-Crown-4, tetraglyme, and triglyme were measured at 25°C in H₂O and D₂O. The contribution of the -CH₂CH₂O- group to the limiting partial molar volumes and compressibilities of cyclic and open-chain ethers in both solvents are compared and solvent isotope effects calculated. It is concluded, based on the compressibility results, that there is a subtle difference between the hydration of the ethene oxde group in cyclic and open-chain ethers and that this difference persists in D₂O. These results indicate that the calculation of limiting apparent molar compressibilities using additivity schemes will have to account for whether the group is in a cyclic or open-chain compound.     

Ab initio Study of H2O–HCl (1:1, 1:2, 2:1) Complexes

This paper reports on an ab initio (6-31G**) study of 1:1, 1:2, and 2:1 (H₂O) _n (HCl) _m complexes. Stable configurations of the 1:2 and 2:1 (H₂O) _n (HCl) _m complexes and their geometrical and energy characteristics were determined. The vibrational analysis of the complexes was carried out. The effect of hydrogen bonding due to S₁S₀ and T₀T₁ electronic excitations is considered.     

Conductance of Some 1:1 Electrolytes in N,N-Dimethylacetamide at 25°C

Precise conductance measurements of solutions of lithium chloride, lithium bromide, lithium iodide, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, tetrabutylammonium bromide, and tetrabutylammonium tetraphenylborate in N,N-dimethylacetamide are reported at 25°C in the concentration range 0.005–0.015 mol-dm^–3. The conductance data have been analyzed by the 1978 Fuoss conductance equation in terms of the limiting molar conductance (⁰), the association constant (K _a), and the association diameter (R). The limiting ionic conductances have been estimated from an appropriate division of the limiting molar conductivity of the reference electrolyte Bu₄NBPh₄. Slight ionic association was found for all these salts in this solvent medium. The results further indicate significant solvation of Li⁺ion, while the other ions are found to be unsolvated in N,N-dimethylacetamide.     

Thermodynamic properties of o-phthalic acid and its products of dissociation at 0–200°C and 1–5000 bar

Values of the pH for four solutions in a KHPh-HCl-KOH system, where Ph denoting C₈O₄H₄, are measured at 25–70°C depending on pressure (1–1000 bar). The experimental results and the available literature data are processed on the base of Helgeson-Kirkham-Flowers (HKF) equation of state [1] and the GIBBS, OptimA, and OptimB programs from the HCh software package [2]. The obtained standard thermodynamic properties and HKF parameters of H₂Ph_aq, HPh^?, and Ph^2? aqueous species, provides calculation of the pH of phthalate buffers in a wide range of temperatures (up to 200°C) and pressures (up to 5 kbar). The calculated values for the biphthalate buffer (0.05m KHPh) correspond to the IUPAC recommendations (at 0–50°C and 1 bar) with an accuracy of 0.005 pH units, and to the values of pH measured in this study at elevated Tp parameters (25–70°C and pressures of up to 1 kbar) within the limits of ±0.02 pH units.     

Partial Molar Volumes of Transfer of Some Amino Acids from Water to Aqueous Glycerol Solutions at 25°C

Apparent molar volumes of glycine, DL--alanine, L-valine, L-leucine, and L-phenylalanine in 0.5, 1.0, 2.0, 3.5, and 5.0 m _B (mol-kg^–1) aqueous solutions of glycerol have been obtained from solution densities at 25°C using precise vibrating-tube digital densimeter. The estimated partial molar volumes at infinite dilution V ^o ₂ have been used to obtain the corresponding transfer volumes _tr V ₂ ^o from water to different glycerol–water mixtures. The transfer volumes are positive for glycine and DL--alanine, and both positive and negative for the other amino acids over the concentration range studied. Interaction coefficients have been obtained from McMillan–Mayer approach and the data have been interpreted in terms of solute–cosolute interactions.     

Thermodynamic properties of the system NH4NO3–KNO3–H2O at 298.15 K

The water activity and osmotic coefficients of the system {y NH₄NO₃+(1-y) KNO₃}(aq) has been measured at total molalities from 0.2 mol kg⁻¹ to about saturation of one of the solutes for different ionic-strength fractions y of NH₄NO₃ with y=0.2, 0.5 and 0.8 at the temperature 298.15 K using the hygrometric method. The obtained data allow the deduction of the thermodynamic parameters. From these measurements, new Pitzer ionic mixing parameters are determined and used to predict the solute activity coefficients in the mixture. The results obtained are used to calculate the excess Gibbs energy at total molalities for different ionic-strength fractions of NH₄NO₃.     

Theoretical Study on Mechanism of C5H7·+O2 Reaction

The potential energy surface (PES) for the reaction of E,E-pentadienyl with molecular oxygen was theoretically studied at the G3B3//B3LYP/6-311G(d,p) level of theory. The first step of the reaction was found to be the direct adduction of molecular O2 on either the C1 or the C3 atoms of E,E-pentadienyl, forming two C5H7O2· isomers. These two C5H7O2· isomers undergo a series of isomerization processes through either the hydrogen-transfer or cyclization pathway. In the final step, the hydrogen-transferred and cyclized isomers decompose into unsaturated aldehydes, unsaturated ketones, and hydroxyl radicals. Involves 20 stable species and 14 transition states, and the energies and structures of all reactants, products and transition states were calculated. Based on the calculated barriers and heats of formation, the authors suggest that the C2H3O·+C3H4O formation channel is the dominant channel for the C5H7·+O2 reaction. The possible existence of C5H7O2· radicals as long lifetime intermediates is also proposed, which is consistent with the recent photoionization mass spectrometric experiments by Zils et al.