Standard Gibbs Energy Research Articles

Origin of the correlation between the standard Gibbs energy of ion transfer and the solubility of water in organic solvents

Standard Gibbs energies ΔwoGi0 of the Cs+ and Li+ ion transfer from water to 1,2-dichlorobenzene, and to an n-octanol + α,α,α-trifluorotoluene mixture were obtained from the steady-state voltammetric measurements. The equilibrium concentrations of water in these solvents were determined by the Karl Fischer method. Analogous data have previously been reported for the transfer of these ions to α,α,α-trifluorotoluene, 1.6-dichlorohexane, 1,4-dichlorobutane, 1,2-dichloroethane, o-nitrophenyl octyl ether, nitrobenzene, and n-octanol. Based on this collection of data, a correlation was established between the experimental values of ΔwoGi0 for the Cs+ or Li+ ion transfer and the reported content of water in the organic solvent characterized by the ratio cW/cS of the molar concentrations of water (cW) and the organic solvent molecules (cS) in the organic solvent S. This correlation exhibits a rapid decay of ΔwoGi0 in the range of the small values of the ratio cW/cS= 0.0025 - 0.02, while towards higher values of cW/cSthe standard Gibbs energy of ion transfer tends to attain a constant value. The relationship was successfully simulated using the equations derived for a Born-type electrostatic model of solvation of the ion, which was combined with a thermodynamic model of the preferential solvation in the mixed solvents. The mechanism of an ion transfer assumes the partial replacement of the water molecules in the first hydration layer of the transferred ion by molecules of the organic solvent. Spectroscopic evidence is presented pointing to the absence of water clusters in pure 1,2-dichloroethane saturated with water, which therefore should not play a role in the ion transfer mechanism.

Effect of Solvation on Glycine Molecules: A Theoretical Study.

Ab initio calculations of HF+MP2 and DFT-B3LYP quality have been used in calculating the molecular geometries and properties of neutral and charged molecules of glycine in amino acid as well as zwitterionic forms. A traditional set of molecular descriptors has been enriched by the molecular chemical potential, expressed via the Mulliken electronegativity, and Pearson's chemical hardness. In the global energy minimum, the complete vibrational analysis allowed evaluating the standard Gibbs energy and related thermodynamic quantities.

Experimental and theoretical approaches to interactions between DNA and purine metabolism products

Deoxyribonucleic acid (DNA) is a significant target for small organic and inorganic drug molecules. Understanding the DNA interaction mechanism of these molecules is vital for new drug designs. In this work, interactions between xanthine (XT), theophylline (TP), and theobromine (TB) with calf-thymus double-strained DNA (dsDNA) were monitored via an experimental and theoretical approach. Experimentally, cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques were used on the surface of the NiO/MWCNT/NNaM/PGE electrochemical platform in vitro. Kinetic parameters, including diffusion coefficients, surface concentrations, and standard heterogeneous rate constants, were measured in the absence and presence of DNA using scan rate studies. In the presence of DNA, kinetic parameters were observed to be reduced significantly. Thermodynamic parameters, such as DNA binding constants and standard free Gibbs energies, were calculated for each molecule using the CV and DPV techniques. Both techniques suggested a binding affinity order of XT > TB > TP. Theoretically, density functional theory was applied for geometry optimization, natural bond orbital analyses, and molecular orbital energies of XT, TP, and TB. Experimental and theoretical binding affinities confirm each other. The most energetically stable ligand-DNA complexes expressed that XT, TP, and TB interact with dsDNA via minor groove binding mode, using mostly hydrogen bonds.

Electrical Conductivity and Ionic Association in Tetraalkylammonium Ionic Liquids in Acetonitrile Solutions

A study is performed of the electrical conductivity (EC) of ionic liquids based on quaternary triethylalkylammonium salts with tetrafluoroborate and hexafluorophosphate anions in acetonitrile. Conductometric data on these compounds are analyzed. Constants Ka of the ionic association of the limiting molar electrical conductivity (λ0) and the standard Gibbs energy of association (ΔG0) in solutions are calculated using the Lee–Wheaton formula. The Stokes radii, limiting mobility, and limiting coefficients of diffusion are found for tetraalkylammonium cations.

SODALITE: SPECTROSCOPIC AND THERMOCHEMICAL INVESTIGATIONS

Two sodalite samples (sample I is Na8Al6Si6O24Cl2⋅0.4H2O from the Kovdor alkaline ultramafic massif with carbonatites in the Murmansk region, Russia, and sample II is Na8Al6Si6O24Cl2⋅0.2H2O from the Bayan Kol nepheline syenite and miaskite massif in the Republic of Tyva) were studied by thermal and electron-microprobe analyses, powder X-ray diffraction, photoluminescence, and by IR, Raman, and ESR spectroscopy. Solution melt calorimetry was applied to determine the enthalpy of formation from elements for water-bearing sodalite samples: −13536 ± 10 (I) and −13503 ± 19 (II) kJ/mol. The enthalpy of formation of sodalite of the theoretical composition Na8Al6Si6O24Cl2 was evaluated at ΔfH0(298.15 K) = −13446 ± 11 kJ/mol. The data obtained on the enthalpy of formation of sodalite and literature data on its S0(298.15 K) were used to calculate the standard Gibbs energies of formation of anhydrous and of water-bearing sodalite.

Thermodynamic properties of the ternary system (KBr + PEG 4000 + water) by potentiometric method at T = (288.2, 298.2, and 308.2) K

The goal of this research is to evaluate the mean ion activity coefficients (γ±) of the mixtures containing KBr + PEG 4000 + H2O (PEG stands for poly(ethylene glycol)) as well as some other thermodynamic quantities including solvent osmotic coefficients (φ), excess Gibbs energies (GE), standard Gibbs energies of transference (ΔGt0), and primary hydration number (nhydr). The experiment was employed by potentiometric measurement using the cell with two ion-selective electrodes (abbreviated as ISE) at (288.2, 298.2, and 308.2) K, and the mass fraction of PEG 4000 ranged from w = (0 to 0.20) with an increment of 0.05. The type of the cell is as follows:K–ISE | KBr (m), PEG 4000 (w), H2O (1-w) | Br–ISE.Nernst's equation was used to combine the Debye-Hückel and Pitzer models with potentiometric values. Pitzer ion interaction parameters (β0, β1, and Cφ) and Debye-Hückel model parameter (a) were evaluated. Moreover, the Bjerrum parameter (q) was calculated.

Thermodynamic method for analyzing and optimizing pretreatment/anaerobic digestion systems

This paper builds a quantitative thermodynamic model for the microbial hydrolysis process (MHP, which uses Caldicellulosiruptor bescii at 75°C for pre-digestion) for producing biogas from a 5-10% aqueous suspension of dairy manure (naturally buffered near pH 7.8 by ammonium bicarbonate) by anaerobic digestion with a mix of acetoclastic and syntrophic methanogenesis. Standard Gibbs energy changes were calculated for the major reactions in pre-digestion, for reactions producing H2, acetate, and CO2 in the digester, and for methanogenesis reactions in the digester. The available data limit the study to analyzing reactions in the digester to reactions of short-chain volatile fatty acids anions. Results are presented as curves of ΔrxnG (Gibbs energy change) vs. acetate concentration. The H2(aq) concentration must be above 1.2×10-9 M to get significant syntrophic methanogenesis, i.e., for ΔrxnG to be negative. The results show syntrophic methanogenesis of propionate, butyrate, and valerate slows as acetate concentration increases because hydrogen production also decreases, and consequently, biogas production from syntrophic methanogenesis slows as acetate increases. Bicarbonate also inhibits both acetoclastic and syntrophic methanogenesis but is necessary to prevent acidification (souring) of the digester. At identical steady-state conditions, acetoclastic methanogenesis runs about 1.4 times faster than syntrophic methanogenesis. Because syntrophic methanogenesis produces acetate catabolized by acetoclastic methanogens, both types of methanogens are necessary to maximize biogas production. The culture in the digester is predicted to evolve to optimize the ratio of acetoclastic methanogens to syntrophic methanogens, a condition signaled by a constant, low acetate concentration in the digester effluent. Obtaining volatile solids reduction as high as 75% with MHP requires a feedstock with less than 25% lignin and a culture of acetoclastic methanogens and syntrophic methanogens and their symbiotic bacteria.

HERBAL INFUSIONS AS INHIBITORS OF TRYPSIN ACTIVITY IN WATER AND POLAR ORGANIC SOLVENT–WATER SYSTEMS

The inhibition of digestive enzyme trypsin by polyphenolic compounds derived from mountainous herbal infusions, as well as the effect of polarity and acidity of the media on this process were studied by virtue of UV-Vis absorption spectroscopy at 293.15 K. Mountainous herbal infusions (thyme, peppermint) are well known due to their biomedical significance and wide use as a beverage. The binding constant (Kb) and standard Gibbs energy change (ΔG0) were calculated. The obtained results show that polyphenols extracted from herbal infusions significantly inhibit trypsin. Moreover, the effect of thyme infusion is stronger compared with that of peppermint. The results show that the change of both polarity and H-bonding ability of polar organic cosolvent significantly alters the value of Kb, indicating that H-bonds and electrostatic interactions are the main driving forces in these interactions.

Proton solvation: competition between acetone and dimethyl sulfoxide

This paper presents results of quantum-chemical study of proton exchange equilibrium between acetone (AC) and dimethyl sulfoxide (DMSO). Basing on the previous study of acid-base equilibria in AC with small additives of DMSO, the most probable composition of the lyonium ion is taken as H(DMSO)2+. The equilibrium geometries and energies of solvents molecules and all possible combinations of proton complexes with one or two solvent molecules were calculated in DFT level of theory using B3LYP functional and 6-31G++(d,p) basis set. The energies of solvated proton complexes were then calculated using PCM method. The energy change corresponding to the equilibrium H(AС)2+ + 2 DMSO ⇄ H(DMSO)2+ + 2 AС is –63.1 kJ mol–1 in the gas phase, which is in qualitative agreement with the standard Gibbs energy data, obtained experimentally in the gas phase by Kebarle’s group, –77.6 kJ mol–1, and with ΔGo298 = –49.3 kJ mol–1 for AC solution with small additions of DMSO, determined by the Guss and Kolthoff method.

Preparation, thermal properties and electrical conductivity of solutions of pyridinium ionic liquids with tetrachloroferrate anion

Thermal stability of N -alkylpyridinium tetrachloroferrates(III) [C5H5NR]FeCl4 [R = C4H9, (CH2)3CN, CH2C6H5, C8H17, C10H21] in air in the range of 25-600°C was studied, as well as the thermal stability of N -alkylpyridinium chlorides. The equivalent electrical conductivity of N -alkylpyridinium tetrachloroferrates(III) in acetonitrile solution at 25°C was investigated. The ionic association constants K a , the limiting molar electrical conductivity (λ0) and the standard Gibbs energy of the association (Δ G °) in acetonitrile solutions were calculated based on conductometric data by the Lee-Wheaton method.

Thermodynamic Properties of Sm3Cl7 Chloride in the Standard State at 298.15 K

The EMF in the 473–728 K range of temperatures is measured for solid-phase galvanic cells (‒) Sm|SmCl2||BaCl2||SmCl3|Sm3Cl7 (+), (–) Sm|SmCl2||BaCl2||Sm3Cl7|SmCl2 (+), (–) SmCl2|Sm3Cl7|| BaCl2||SmCl3|Sm3Cl7 (+), and (–) Mg|MgCl2||BaCl2||SmCl3|Sm3Cl7 (+). Experimental data are processed according to the second law of thermodynamics using literature values of thermodynamic characteristics of the components of the EMF-forming reaction: Sm, Mg, SmCl2, SmCl3, and MgCl2. Values of the standard Gibbs energy of formation, the standard enthalpy of formation, and the standard entropy of chloride Sm3Cl7 at a temperature of 298.15 K are obtained by averaging data on four galvanic cells.

On the estimation of standard adsorption free energy from corrosion inhibition efficiencies

The standard adsorption Gibbs energy ( ▪ ) is often estimated by assuming that the corrosion inhibition efficiency is equivalent to fractional surface coverage. However, Lindsay et al. [Corros. Sci. 155 (2019) 182–185] demonstrated that this assumption is not necessarily valid. Therefore, a model that maps inhibition efficiency to fractional surface coverage is developed herein to provide a more reliable estimation of ▪ . The model is validated with the experimental data of Lindsay et al.; the analysis confirms their conclusion that a significant error in ▪ estimation can be made by using inhibition efficiency as a proxy for surface coverage.

A general-purpose adsorption isotherm for improved estimation of standard adsorption free energy

A new general-purpose Type–I adsorption isotherm is proposed to improve standard adsorption Gibbs energy estimation. This new isotherm stems from considering a functional dependence of various adsorption models on the c/θ vs. c plot, where θ is the fractional surface coverage and c the concentration. It can accurately describe many adsorption isotherms, implying that it is flexible enough to describe various adsorption scenarios. Among the tested adsorption models that the new isotherm can describe are those that consider lateral inter-adsorbate interactions, molecular size, surface heterogeneity, and mobile adsorption.

On the use of the Langmuir and other adsorption isotherms in corrosion inhibition

In corrosion inhibition studies, the standard adsorption Gibbs energy is often estimated via the linear regression of the Langmuir isotherm in the c/θ=1/K+c form, where both the intercept and the slope are estimated, although the Langmuir isotherm requires the slope of 1. Hence, c/θ=1/K+mc is actually used, where m is the slope. Herein, a theoretical basis for this equation is established. It is demonstrated to be an effective equation that can decently describe various adsorption models and provide relatively accurate estimates of the standard adsorption Gibbs energy, provided surface coverages are reliably determined experimentally. However, any significant deviation from the slope of 1 signals non-Langmuir adsorption due to inter-adsorbate interactions, multi-site adsorption, or surface heterogeneity. Among these three causes, only attractive inter-adsorbate interactions lead to a slope of less than 1.

Effect of water solubility in organic solvents on the standard Gibbs energy of ion transfer across a water/organic solvent interface

Ion transfer voltammetry is used to study the transfer of alkali metal and proton cations and the Cl− anion from the aqueous solution of MCl (M+ = H+, Li+, Na+, K+, Rb+, Cs+) to the solution of bis(triphenylphosphoranylidene)ammonium tetrakis(pentafluorophenyl)borate in α,α.α-trifluorotoluene (TFT) or 1,2-dichloroethane (DCE). The scale of the applied potentials is converted to the scale of the Galvani potential differences on the basis of the voltammetric measurements of the standard ion transfer potential for the tetraethylammonium (TEA+) ion used as a reference ion in situ. The interfacial tension measurements at the water/TFT interface yield the zero-charge potential difference, which is close to the expected zero value. The standard Gibbs energies of ion transfer ΔwoGi0 are evaluated from the voltammetric data on considering both the effect of the association between the transferred ion and the counter-ion of the organic solvent phase, and the effect of the ion migration in the aqueous phase. The values of ΔwoGi0 for the ion transfer to TFT are found to be considerably higher than those obtained for the ion transfer to DCE. This difference is proposed to be related to the significantly lower solubility of water in TFT, possibly requiring the removal of the ion hydration shell in the course of the ion transfer from water to TFT. Such conclusion is supported by the calculations of ΔwoGi0 by using an advanced Born-type model of ion solvation.

Phase Transitions Equilibria of Five Dichlorinated Substituted Benzenes.

This work reports an experimental study aiming to determine the thermodynamic properties of five chlorinated compounds with environmental impact. The vapor pressures of the crystalline phases of three isomers of dichlorobenzoic acid (2,4-, 2,5-, and 2,6-) and 2,6-dichlorobenzonitrile were measured at several temperatures using the Knudsen effusion technique. Another technique (a static method based on capacitance diaphragm manometers) allowed the measurement of the vapor pressures of both the crystalline and liquid phases of 2,4-dichlorobenzonitrile between 303.0 and 380.0 K. This latter technique also enabled the measurement of sublimation vapor pressures of 2,6-dichlorobenzonitrile over a larger range interval of temperatures, T = 328.7 and 391.8 K. The standard molar enthalpy, entropy, and Gibbs energy of sublimation (for all the compounds studied) and vaporization (for 2,4-dichlorobenzonitrile) were derived, at reference temperatures, from the experimental vapor pressure results. The temperatures and enthalpies of fusion and the isobaric heat capacities of the five crystalline-substituted benzenes were determined using differential scanning calorimetry. The contributions of the three substituents (-COOH, -CN, and -Cl) to the sublimation thermodynamic properties of the compounds studied were discussed.

Universal Langmuir and Fractal Analysis of High-Resolution Adsorption Isotherms of Argon and Nitrogen on Macroporous Silica.

High-resolution isotherms of argon and nitrogen adsorption on macroporous silica have been simulated with universal Langmuir and fractal models. A four-parameter, fractal universal Langmuir equation is a good fit to the data at low pressures. Standard Gibbs energy changes calculated from equilibrium adsorption coefficients show a series of broad peaks that indicate adsorbate structural transformations as a function of pressure and coverage. The Freundlich equation or mean fractal model is also a good fit to isotherms at low pressures. Pressure-varying fractals are accurate fits to the data. Fractal exponents provide information on adsorbate coverage and surface access. Broad peaks in pressure-varying exponents are indicators of adsorbate structure. From adsorptive gas amounts, mean and pressure-varying fractal exponents provide details of adsorbate fractal dimensions and surface roughness. Both Ar and N2 adsorption cause increases in mean surface roughness when compared with pure silica. Surface roughness fluctuations from pressure-dependent adsorptive gas fractal dimensions are associated with adsorbate structure. At one trough, the surface is smooth and is linked to close-packed Ar or N2. For Ar adsorption at 87 K, this structure is a complete monolayer (1.00(4)), while for Ar (77 K), 1.15(4) layers and for N2 (87 K), 2.02(10) layers. The universal Langmuir specific area of the silica is 10.1(4) m2 g-1. Pressure- and coverage-dependent adsorbate structures range from filling defects and holes on the surface to cluster formation to adsorbed Ar or N2 evenly distributed or packed across the surface. The Ar (87 K) isotherm is most sensitive to adsorbate structural transformations.

Ligand-Modulated Nuclearity and Geometry in Nickel(II) Hydrazone Complexes: From Mononuclear Complexes to Acetato- and/or Phenoxido-Bridged Clusters.

The propensity of 4-hydroxybenzhydrazone-related ligands derived from 3-methoxysalicylaldehyde (H2L3OMe), 4-methoxysalicylaldehyde (H2L4OMe), and salicylaldehyde (H2LH) to act as chelating and/or bridging ligands in Ni(II) complexes was investigated. Three clusters of different nuclearities, [Ni3(L3OMe)2(OAc)2(MeOH)2]∙2MeOH∙MeCN (1∙2MeOH∙MeCN), [Ni2(HL4OMe)(L4OMe)(OAc)(MeOH)2]∙4.7MeOH (2∙4.7MeOH), and [Ni4(HLH)2(LH)2(OAc)2]∙4MeOH·0.63H2O·0.5MeCN·HOAc (3∙4MeOH·0.63H2O·0.5MeCN·HOAc), were prepared from Ni(OAc)2∙4H2O and the corresponding ligand in the presence of Et3N. The hydrazones in these acetato- and phenoxido-bridged clusters acted as singly or doubly deprotonated ligands. When pyridine was used, mononuclear complexes with the square-planar geometry seemed to be favoured, as found for complexes [Ni(L3OMe)(py)] (4), [Ni(L4Ome)(py)] (5) and [Ni(LH)(py)] (6). Ligand substituent effects and the stability of square-planar complexes were investigated and quantified by extensive quantum chemical analysis. Obtained results showed that standard Gibbs energies of binding were lower for square-planar than for octahedral complexes. Starting from [MoO2(L)(EtOH)] complexes as precursors and applying the metal-exchange procedure, the mononuclear complexes [Ni(HL3OMe)2]∙MeOH (7∙MeOH) and [Ni(HLH)]∙2MeOH (9∙2MeOH) and hybrid organic-inorganic compound [Ni2(HL4OMe)2(CH3OH)4][Mo4O10(OCH3)6] (10) were achieved. The octahedral complexes [Ni(HL)2] (7-9) can also be obtained by the direct synthesis from Ni(Oac)2∙4H2O and the appropriate ligand under specific reaction conditions. Crystal and molecular structures of 1∙2MeOH∙MeCN, 2∙4.7MeOH, 3∙4MeOH∙0.63H2O∙0.5MeCN∙HOAc, 4, 5, 9∙2MeOH, and 10 were determined by the single-crystal X-ray diffraction method.

Thermodynamic and magnetic properties for Dy2Fe14B determined by heat capacity measurement from very low to high temperatures and solution calorimetry

The thermodynamic and magnetic properties for Dy2Fe14B, a principal constituent of rare-earth magnets, were investigated as a function of temperature via calorimetric measurements. Its standard entropy, Δ0TSm∘, was obtained from the molar heat capacity, Cp,m∘, at 2 − 850 K using Debye-Einstein spin-wave functions. The standard enthalpy of formation, ΔfHm∘, was determined by acid solution calorimetry to provide the standard Gibbs energy of formation ΔfGm∘(T) as a function of temperature. ΔfGm∘(T) is useful for Calphad phase diagram calculations. The magnetic moment was calculated by separating the spin and lattice vibration terms for Cp,m∘ via the Curie temperature of 594.1 K. The results agree with direct magnetization measurements and indicate that the Fe 3d magnetic moments magnetize Dy2Fe14B by aligning by an exchange interaction between the Dy 4f and Dy 5d and Fe 3d moments in a second-order phase transition. These findings will contribute to the design of magnetic materials.

Identification of Nano-Metal Oxides That Can Be Synthesized by Precipitation-Calcination Method Reacting Their Chloride Solutions with NaOH Solution and Their Application for Carbon Dioxide Capture from Air-A Thermodynamic Analysis.

Several metal oxide nanoparticles (NPs) were already obtained by mixing NaOH solution with chloride solution of the corresponding metal to form metal hydroxide or oxide precipitates and wash-dry-calcine the latter. However, the complete list of metal oxide NPs is missing with which this technology works well. The aim of this study was to fill this knowledge gap and to provide a full list of possible metals for which this technology probably works well. Our methodology was chemical thermodynamics, analyzing solubilities of metal chlorides, metal oxides and metal hydroxides in water and also standard molar Gibbs energy changes accompanying the following: (i) the reaction between metal chlorides and NaOH; (ii) the dissociation reaction of metal hydroxides into metal oxide and water vapor and (iii) the reaction between metal oxides and gaseous carbon dioxide to form metal carbonates. The major result of this paper is that the following metal-oxide NPs can be produced by the above technology from the corresponding metal chlorides: Al2O3, BeO, CaO, CdO, CoO, CuO, FeO, Fe2O3, In2O3, La2O3, MgO, MnO, Nd2O3, NiO, Pr2O3, Sb2O3, Sm2O3, SnO, Y2O3 and ZnO. From the analysis of the literature, the following nine nano-oxides have been already obtained experimentally with this technology: CaO, CdO, Co3O4, CuO, Fe2O3, NiO, MgO, SnO2 and ZnO (note: Co3O4 and SnO2 were obtained under oxidizing conditions during calcination in air). Thus, it is predicted here that the following nano-oxides can be potentially synthesized with this technology in the future: Al2O3, BeO, In2O3, La2O3, MnO, Nd2O3, Pr2O3, Sb2O3, Sm2O3 and Y2O3. The secondary result is that among the above 20 nano-oxides, the following five nano-oxides are able to capture carbon dioxide from air at least down to 42 ppm residual CO2-content, i.e., decreasing the current level of 420 ppm of CO2 in the Earth's atmosphere at least tenfold: CaO, MnO, MgO, CdO, CoO. The tertiary result is that by mixing the AuCl3 solution with NaOH solution, Au nano-particles will precipitate without forming Au-oxide NPs. The results are significant for the synthesis of metal nano-oxide particles and for capturing carbon dioxide from air.