Values Of Standard Free Energy Research Articles

Two-dimensional classification of amphiphilic monomers based on interfacial and partitioning properties. 2. Amino acids and amino acid residues

A new classification for amino acid residues is proposed, based on interfacial and partitioning properties. Amino acid residues are characterized by two parameters: standard free energy of adsorption at the hexane/water interface and standard free energy of the partition between hexane and water. Theoretical approaches are used for the estimation of these parameters. As a result, several groups of amino acid units having close values of the parameters are distinguished. Classification of the amino acid units by such a method is believed to be able to provide promising results in the search of correlations in protein sequences. The comparison of experimental and theoretical studies of free amino acids at the hexane/water interface confirm the predictive power of the theory used, because a very good coincidence between theoretical and experimental data points is observed. The obtained values of standard free energies of adsorption are consistent with literature data.

Adsorption equilibria of reactive dye onto highly polyaminated porous chitosan beads

The adsorption of vinyl sulfone type reactive black 5 (RB 5) in aqueous solution onto chitosan beads and cross-linked chitosan beads with glutaraldehyde has been investigated in terms of initial pH and temperature of the solution. The adsorption equilibrium data were correlated with three adsorption models, such as Langmuir, Freundlich and Sips isotherms. Among them, the Freundlich isotherm best fit the data over the entire pH and temperature range of the solution. The adsorption capacity of RB 5 onto chitosan beads and cross-linked chitosan beads increased with decreasing initial pH and with increasing temperature. Equilibrium amount of RB 5 on chitosan beads was greater than that of cross-linked chitosan beads at the same initial pH values. Thermodynamic studies have also been carried out and values of standard free energy (°Gℴ), enthalpy (°Hℴ) and entropy (°Sℴ) were calculated.

Corrosion inhibition of mild steel using naphthalene disulfonic acid

The corrosion inhibition of mild steel is the subject of tremendous technological importance due to the increased industrial applications of this material. This paper reports the results of mass loss and potentiodynamic polarization measurements on the corrosion inhibition of mild steel in 0.5 M H2SO4 in the temperature range 30–60 °C using sodium naphthalene disulphonic acid (NDSA) as an inhibitor. The inhibition efficiency increased with the increase in concentration of NDSA till a critical value which is independent on temperature. The adsorption of inhibitor at 30 °C followed Flory–Huggins adsorption isotherm and the value of standard free energy of adsorption suggests that it is chemisorption.

Synthesis and properties of triethylalkylammonium perfluorooctanesulfonates (APFOS)

Six ionic surfactants containing a perfluorooctanesulfonic anion and a positively charged ammonium in a molecule, R FSO 3 −N +Et 3C n H 2 n+1 ( n=2, 4, 6, 8, 10 and 12), were prepared from perfluorooctanesulfonyl fluoride, triethylamine and linear alkanol. Solution properties of triethylalkylammonium perfluorooctanesulfonates (APFOS) have been measured in terms of surface tension. The values of critical micelle concentration (cmc) decrease with an increase of N-alkyl chain length, and the logarithm of the cmc decreases linearly with increasing N-alkyl chain length ( n≥6), while the negative values of standard free energy for the adsorption become larger as the N-alkyl chain length increases.

Removal of Nickel(II) and Zinc(II) from Wastewater Using Fly Ash and Impregnated Fly Ash

Adsorption of toxic metal ions like Ni(II) and Zn(II) on fly ash and impregnated fly ash was studied in terms of different parameters like initial metal ion concentrations, pH, and temperature. Impregnated fly ash showed much higher levels of adsorption capacity for Ni(II) and Zn(II) as compared to untreated fly ash. The various rate parameters governing the adsorption process have been determined at different temperatures. Equilibrium modeling has been carried out using Langmuir isotherm equations, and the corresponding constants have been evaluated. Thermodynamic studies have also been carried out and values of standard free energy (ΔG0), enthalpy (ΔH0), and entropy (ΔS0) calculated. The adsorption was found to be exothermic for Ni(II) and endothermic in case of Zn(II) as determined by the values of enthalpy change.

Evaluation of non-toxic corrosion inhibitors for copper in sulphuric acid

The aim of this paper is to study influence of the molecular structure on the inhibiting properties of organic compounds in corrosion processes in acid media. The inhibiting efficiency of non-toxic imidazole derivatives on copper corrosion in sulphuric acid is investigated. The investigation is performed using electrochemical methods of potentiodynamic polarisation as well as gravimetric measurements. The results of the investigation show that the inhibiting properties of substituted imidazoles depend on molecular structure. The best protection (93%) is obtained by adding a phenyl ring to the imidazole structure. The values of standard free energies of adsorption, as calculated from the Freundlich isotherm, indicate that in the presence of sulphuric acid imidazole derivatives adsorb on copper by a physisorption-based mechanism.

Removal of Heavy–Metal Ions from Solutions by Means of Zeolites. II. Thermodynamics of the Exchange Processes Between Zinc and Lead Ions from Solutions and Sodium Ions from Zeolite A

Relationships between the corrected selectivity coefficient, Kc (Me) (Me = Zn, Pb), and fraction of the exchanged Me2+ ions in zeolite A, f Me,Z, were determined from the corresponding exchange isotherms. The exchange isotherms were obtained by measuring the equilibrium concentrations of sodium and Me2+ ions in both the solid and the liquid phase at constant total-ion concentrations and different temperatures in the range from 20°C to 60°C. Thermodynamic equilibrium constants, Ka (Me), calculated from the corresponding Kielland's plots (lnKC (Me) vs.f Me,Z plots) were used for the calculation of the appropriate values of standard free energy, ΔG°(Me), standard enthalpy, ΔH°(Me), and standard entropy, ΔS°(Me).

Estimating the standard free energy of formation of zeolites using the polymer model

Abstract The standard free energies of formation of a number of zeolites were estimated using the polymer model developed previously for smectites by Sposito. The estimates made with the polymer model were on average within 19 kJ mol −1 (0.28%) of the experimental values for zeolites; this compares with the values estimated by the methods of LaIglesia and Aznar and of Chermak and Rimstidt which differed from the experimental values on average by approximately 27 kJ mol −1 (0.40%) and 32 kJ mol −1 (0.47%) respectively. The values predicted by the polymer model for dehydrated zeolites were within 28 kJ mol −1 (0.3%) of the experimental values, whereas the other two methods generate estimates of free energies of formation values that differed on average by 89 kJ mol −1 (1.28%) and 107 kJ mol −1 (1.59%) from the experimental values. These comparisons indicate that the polymer model, formulated specifically for a class of silicate minerals such as zeolites, always typically provides a better estimate of the standard free energy values than general models for all silicate minerals which contain a number of ad hoc assumptions. Better estimates provided by the polymer model can be attributed to the principle that the free energy changes associated with the formation of condensation polymers, such as zeolites, are related principally with the free energy changes associated with the relative change in coordination of exchangeable cations as they transfer from reactant hydroxide sites to exchangeable sites.

Removal of Heavy Metal Ions from Solutions by Means of Zeolites. I. Thermodynamics of the Exchange Processes between Cadmium Ions from Solution and Sodium Ions from Zeolite A

ABSTRACT Relationships between corrected selectivity coefficient (kc) and fraction of the exchanged cadmium ions in zeolite A (fcd.z) were determined from data obtained by measuring the concentrations of sodium and cadmium ions in both the solid and the liquid phase at equilibrium of the exchange processes between cadmium ions from solution and sodium ions from zeolite A at different total ion concentra- tions and different temperatures. Thermodynamic equilibrium constants (ka ) calculated from the corresponding Kielland's plots (Kc vs fcd.z plots) were used for the calculation of the appropriate values of standard free energy (AG′) standard enthalpy (δH′), and standard entropy (δG′). The influence of the degree of exchange on the activity coefficients of sodium and cadmium ions in zeolite is also considered.

Hydrolysis of Chromium(III) Ion and Solubility of Chromium(III) Oxide in High Temperature Water

Recently, the chemical behaviour of chromium species in the primary circuit of water-cooled nuclear reactors has gained a great deal of attention because of its important role in accumulation of radioactivity onto the surface of piping systems. To elucidate the behaviour of chromium compounds, the thermodynamic approach plays an important role. However, there is no thermodynamic data set of chromium ion at high temperatures. Thus, the acquisition of experimental data was considered to be essential. In this work, values of hydrolysis constants and standard free energy of formation of chromium(III) ion at high temperatures were evaluated experimentally.

リサイクルと環境問題を考える カルシウム化合物浮上分離法によるアルミニウム合金溶湯からの不純物シリコンの除去

When aluminum product scrap is recycled as melting material, it is essential to control impurity elements entering the molten metal from scrap for quality assurance. To date, in order to prevent entry of impurity elements into the molten metal from scrap, solid-phase selection and liquid-phase refining have been used. When an eye is placed on the liquid-phase refining, a segregation process is adopted for manufacturing of high-purity metal, but presently, any process for removing impurity elements from the molten metal obtained by melting scrap has not yet been put in practical use. Therefore, this report places an eye on the so-called compound method. In this method, proper elements were added to the molten metal to form intermetallic compounds with impurity elements to be removed. The impurity elements were removed by removing the compounds from the molten metal. A special attention was placed on silicon as an impurity element to be removed and for an element to be added to form intermetallic compounds, calcium was chosen based on the value of standard free energy of formation ΔG0 of binary compounds containing silicon. With these elements, at least, Ca2Si and CaSi2Al2 are found to form as intermetallic compounds and the silicon concentration in the molten metal is reduced by about 50% in relative values.

Summary of the Apparent Standard Partial Molal Gibbs Free Energies of Formation of Aqueous Species, Minerals, and Gases at Pressures 1 to 5000 Bars and Temperatures 25 to 1000 °C

Accurate values of the apparent standard partial molal Gibbs free energies of formation (ΔḠ°) of aqueous species, minerals, and gases at high temperatures and pressures are a requisite for characterizing a variety of industrial and natural processes including corrosion of metals, solvent extraction, crystal growth, metamorphism, and the formation of hydrothermal ore deposits. Revision of the HKF equations of state for aqueous species other than H2O (Helgeson, Kirkham and Flowers, 1981) by Tanger and Helgeson (1988) and Shock et al. (1992) permits calculation of ΔḠ° for these species at temperatures to 1000 °C and pressures to 5000 bars. The revised equations of state were combined with parameters generated by Shock and Helgeson (1988, 1990), Shock and McKinnon (1993), Shock and Koretsky (1993), Schulte and Shock (1993), Pokrovskii and Helgeson (1995 a, b, and c), and Sverjensky et al. (1995) together with densities and electrostatic properties of H2O computed from equations summarized by Johnson and Norton (1991) to calculate values of ΔḠ° for aqueous species as a function of temperature and pressure. The results of these calculations are tabulated for 348 such species, including both inorganic and organic aqueous ions, neutral species, and metal ligand complexes. Similar calculations using equations, parameters, and thermodynamic data taken from Kelley (1960), Helgeson <etal (1978), Wagman >et al. (1982), Hill (1990), Shock (1993), and Pokrovskii and Helgeson (1995 a and b) were used to generate tables of ΔḠ° for H2O, 22 minerals, and 18 gases. The tabulated values of ΔḠ°, which were generated with the aid of SUPCRT92 (Johnson et al., 1992), facilitate considerably assessment of the thermodynamic behavior of chemical processes at both high and low temperatures and pressures.

Preferential Oxidation of Mg in Mechanically Alloyed Al–Mg–O Based Systems

For the purpose of attesting preferential oxidation of solute Mg in Al and obtaining fine dispersion of MgO in the Al matrix, a powder of Al-10 at%Mg alloy was mechanically alloyed with or without addition of metal oxide. Metal oxides added are CuO, Fe2O3, SiO2, V2O5, Nb2O5 and Ta2O5. MA was carried out under an argon atmosphere by using an Attritor ball mill with addition of methanol as the process control agent. After ball-milling for 30 h, the MAed powders were degassed and consolidated to P/M materials by hot extrusion. The P/M materials were heated at 773 K for 24 h. Constituent phases were studied for the MAed powders, as-extruded and heated P/M materials by X-ray diffraction. Metallography and hardness measurement were also done for the P/M materials.In Al–Mg alloy MAed with methanol, MgO is formed by preferential oxidation. In all the Al–Mg-Metal oxide systems studied, reduction of the added metal oxide and preferential oxidation of Mg were observed at different stages of mechanical and thermal processes. No diffraction lines of Al2O3 were observed throughout. In the Al–Mg–CuO system, decomposition of CuO occurred during ball-milling. In the systems other than Al–Mg–CuO, decomposition of the added oxide and formation of MgO were observed in the as-extruded P/M material. Such a solid state reaction proceeded by further heating at 773 K. After heating for 24 h, decomposition of the added oxides was completed except Ta2O5. The rate of decomposition of metal oxides is in correlation with their values of standard free energy of formation. Thus, in MAed Al–Mg based systems, dispersion of MgO particles in the Al alloy matrix can be attained by preferential oxidation of solute Mg. In case of addition of excess oxygen over MgO equivalent, formation of spinel (MgAl2O4) was observed.

Comparative sorption equilibrium studies of toxic phenols on flyash and impregnated flyash

AbstractIn the present study, the sorption of toxic phenols, which include phenol, o‐cresol, m‐cresol, p‐cresol, o‐nitrophenol, m‐nitrophenol and p‐nitrophenol, has been investigated. The influences of various factors, such as particle size, impregnation of flyash (IFA), pH and temperature on the sorption capacity have been studied. Equilibrium modelling has been carried out using Langmuir and Freundlich isotherm equations and constants have been calculated under different conditions. Thermodynamic studies have also been carried out and values of standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) calculated.

Pictorial representation of solid-gas equilibria at high temperatures

A pictorial representation of solid-gas equilibria is useful for studying the thermodynamics of a system under consideration. These diagrams show the stability regions of the species involved in a system as functions of pressures of two reacting gases. A computer program initially developed to plot the predominance area diagrams for metal-sulfur-oxygen (M-S-O) systems in roasting processes has been modified and generalized to handle any solid-gas system. This program has been utilized to plot the predominance area diagrams (PAD) for metal-sulfur-oxygen and metal-oxygen systems. The only data input required by the computer are the standard free energy values of all species existing in a system.

溶融アルミニウムのｉｎ ｓｉｔｕ酸化による粒子強化複合材料の製造

A new technique for making particulate composites has been investigated. Unstable oxides such as CuO, SnO2 ZnO and Cr2O3 whose absolute value of standard free energy of formation is smaller than that of Al2O3 were added to moleton aluminum and Al-3.0%Mg alloy. Al2O3 particles are formed in Al-Cu matrix by adding CuO to moleton aluminum at 1273K. Furthermore, by adding CuO the moleton Al-3.0%Mg alloy, MgAl2O4 (spinel) particles are formed. No particles are found in the pure aluminum matrix by adding either SnO2 Or ZnO because of the poor wettability between these oxides and moleton aluminum. However, in case of Al-3.0%Mg alloy matrix, MgAl2O3 particles are formed by adding these oxides because the wettability is improved by presence of magnesium. On the other hand, by addition of Cr2O3, whose absolute value offree energy of formation is relatively large and close to that of Al2O3, in situ particles are formed in neither pure aluminum nor Al-3.0%Mg alloy matrix. The size and shape of particles formed by the in situ reaction depend on temperature of molten metal. The size of in situ particles increases and the shape becomes complicatedly with increase in the temperature of reaction. Although oxide particles formed in this experiment are small and some of them are under 1μm in diameter, macroscopic distribution is not uniform.

Protolytic equilibria of several 4‐acyl‐substituted 1‐phenyl‐3‐methylpyrazol‐5‐ones in dioxane–water mixtures

AbstractThermodynamic proton ionization constants, TpKa, of several 4‐acyl‐substituted pyrazol‐5‐ones [acyl = trifluoroacetyl (HPMTFP), acetyl (HPMAP), hexanoyl (HPMHP)] were determined in various dioxane–water mixtures at 25 and 35 ± 0.1°C. The TpKa values were determined by glass‐electrode potentiometry and refined by using the extensive weighted least‐squares FORTRAN program TPKA. Both extrapolation and leastsquares methods were used to obtain TpKa values in pure water (0%). All three acyl derivatives are weak monoprotic acids with TpKa values between 2.5 and 3.9, following the order HPMTFP < HPMAP ≤ HPMHP. The TpKa values do not vary linearly with the reciprocal of the dielectic constant of the medium; however, a plot of TpKa versus the mole fraction of dioxane, n2, is linear at a given temperature. Values of standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes associated with their protolytic equilibria were also calculated. Temperature, medium and substituent effects are briefly discussed.

Adsorption for removal of Cd(II) from effluents

The adsorption of Cd(II) onto wollastonite has been reported. Adsorption increased from 55.7 to 93.6% by decreasing the concentration of Cd(II) from 2.0 x 10‐4M to 0.5 x 10‐4M. The rearranged Lagergren equation has been used for dynamic modelling of the process. However, the value of rate constant at 30°C was found to be 3.17 x 10‐2min‐1. Equilibrium modelling was carried out using the Freundlich isotherm equation and constants have been calculated. Thermodynamic studies were carried out and values of standard free energy (?G°), enthalpy (?H°) and entropy (AS°) were calculated at various temperatures. Low temperatures favour the uptake of Cd(II) in the process.

Thermodynamic Proton Ionization Constants of some fluorinated β‐ketoesters in dioxane‐water mixtures. Influence of terminal group substitution

AbstractThermodynamic proton ionization constants, TpKa, of methyl trifluoroacetoacetate (HMTAA), ethyltrifluoroacetoacetate (HETAA) and ethylpentafluoropropionylacetate (HEPPA) have been determined in 10–50% dioxane‐water mixtures at 25 and 35 ± 0.1°C applying an empirical pH correction for mixed aqueous‐organic media. The TpKa values are calculated by subjecting the experimental data to rigorous weighted least‐squares analysis. Further, a least‐squares extrapolation technique is applied to evaluate TpKa in pure water (0% dioxane). All the three ligands are weak monoprotonic acids with their TpKa between 6.0 and 9.0. Plots of TpKa with the reciprocal of the dielectric constants of the medium are not linear but plots of TpKavs. mole fraction of dioxane are linear at a given temperature. Values of standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes, associated with their ionization are also computed. Temperature, medium and substituent effects are briefly discussed.

Thermodynamics of ion solvation in mixed aqueous solvents. Part 2.—Effect of steric hindrance on free energies of transfer of cations; correlations with structural determinations

Precise values of the standard free energies of transfer, ΔG°t, from water to mixtures of water with methanol, t-butyl alcohol (TBA), acetone and dioxane are available for the alkali-metal and silver chlorides and for hydrochloric acid, together with a few values for chlorides of bivalent metals in the two alcohol systems. These values are discussed from the standpoint of steric hindrance to solvation. When a more basic ligand replaces water in a cation–solvent complex, the lowering of free energy arising from the stronger acid–base interaction is offset by the effects of any resultant steric hindrance to solvation. The Feakins–Watson ‘acid–base’ theory suggests a simple electrostatic model, which is applied quantitatively to Li+, Na+, H+ and Ag+. The behaviour of Ag+ and H+ is quantitatively reproducible from system to system and is consistent with no steric hindrance of either ion up to ca. 60%(w/w) organic solvent. Li+ and Na+ are unhindered in methanol–water mixtures; steric hindrance of Li+ in other mixtures increases in the order dioxane < acetone < TBA; Na+ is hindered only in TBA–water. Geometries recently found for the aqueous complexes from neutron diffraction experiments and MD calculations are reviewed. The coordination numbers (n): Li+(6), Na+(6) and Ag+(4) yield O—O distances for adjacent ligands which are completely consistent with the above observations. Since the ion–ligand interaction energy is proportional to n, Ca2+(10) should have a lower ΔG°t than an alkali-metal ion of the same size. The alkaline-earth-metal ions should also be vulnerable to steric hindrance by TBA if Na+ is. Both conclusions are verified. The values for Cs+ also fit the electrostatic model fairly well, although they would also be consistent with an additional non-electrostatic interaction in this case. The O—O distance in the Cs+ complex (n= 8) is about the same as in the Ag+ complex, but the lower O—M—O will make Cs+ more vulnerable to steric hindrance. Cs+ is unhindered in aqueous methanol, dioxane and acetone, but hindered in TBA–water, although less than Li+ and Na+. For Ag+ the structural and thermodynamic findings, of uncrowded stereochemistry and strong metal–oxygen bonds relative to those of the alkali metals, suggest weak and stereochemically selective shielding of the nucleus by the d electrons. The limited thermodynamic evidence suggests that this may also be true for Zn2+ and Cd2+, which also have d10 configurations, and would also support a relatively low n (ca. 7) for Cd2+.