Experimental Evaluation of ΔS°rxn, ΔH°rxn, and ΔG°rxn Using Voltaic Cells: A First-Year College Chemistry Laboratory

Six voltaic cells have been evaluated for their suitability in the determination of thermodynamic parameters. The cells were prepared with all species present at conditions that approximate standard-state conditions and cell potentials were measured as a function of temperature. From these measurements graphs of voltage versus temperature were prepared. From these graphs it was possible to determine the standard heats of reaction (II_rxn), standard change in entropy or disorder (S°_rxn), and the Gibbs free energy (G°_rxn) for the spontaneous oxidation-reduction reactions. The standard cell potential (E°_cell values were also calculated. Two cells with opposite temperature dependence of the cell potential were found to produce good agreement with the literature values of G°_rxn, H°_rxn, S°^rxn and E°_cell. Criteria for identifying additional cells that may be suitable for potentiometric studies of thermodynamic parameters are also included.     

Enthalpies of Dilution of Aqueous Solutions of HCl, MgCl2}, CaCl2, and BaCl2 at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of BaCl₂ at 300°C and 11.0 MPa, MgCl₂, CaCl₂, and BaCl₂ at 325°C and 14.8 MPa, and at 350°C and 17.6 MPa. Previously collected dilution enthalpies for aqueous solutions of MgCl₂ and CaCl₂ at 300°C and 10.3 MPa and for aqueous solutions of HCl at 250, 275, and 300°C at 10.3 MPa and 320°C at 12.8 MPa were included with the new data at 300°C and 11.0 MPa and at 350°C and 17.6 MPa when fitting the Pitzer parameters. The concentration range of the chloride solutions was 0.5 to 0.02 molal. Parameters for the Pitzer excess Gibbs ion–interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat-capacity changes for the association of alkaline earth metal ions and H⁺ with chloride ion were estimated from the heat data. For all systems, the enthalpy and entropy changes are positive and show accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.     

Thermodynamics of protonation of AMP,ADP, and ATP from 50 to 125°C

The interaction of adenosine 5-monophosphate (AMP), adenosine 5-diphosphate (ADP), and adenosine 5-triphosphate (ATP) ions with protons in aqueous solution has been studied calorimetrically from 50 to 125°C and 1.52 MPa. At each temperature, the reaction of acidic AMP with tetramethylammonium hydroxide was combined with the heat of ionization for water to obtain the enthalpy of protonation of AMP, while the reactions of HCl with deprotonated tetramethylammonium salts of ADP and ATP were used to obtain the enthalpies of protonation of ADP and ATP. Equilibrium constant K, enthalpy change H^o, entropy change S^o, and heat capacity change C _p ^o values were calculated for the stepwise protonation reactions as a function of temperature. The reactions involving the first protonation of AMP, ADP, and ATP and the third protonation of ADP and ATP were endothermic over the temperature range studied, while that involving the second protonation is exothermic for AMP and ADP, but is exothermic below 100°C and endothermic at 125°C in the case of ATP. Consequently, log K values for the first and third protonation reactions (phosphate groups) increase while those for the second protonation reaction (N₁-adenine) decrease in the cases of AMP and ADP and go through a minimum in the case of ATP as temperature increases. The H^o values for all protonation reactions increase with temperature. The magnitude and the trend for the H^o, S^o, and C _p ^o values with temperature are discussed in terms of solvent-solute interactions. The magnitude of the C _p ^o values for the second protonation is consistent with little interaction between the phosphate ion and the protonated N₁ site of the adenine moiety in AMP, but indicates moderate interaction between these groups in ADP, and strong interaction in ATP.     

Electric conductivities of S-alkylisothiouronium salts in nitrobenzene and methanol at 25, 35, and 45°C

Conductance data for dilute solutions of S-n-butylisothiouronium bromide and iodide salts as well as S-alkylisothiouronium picrates (alkyl=methyl to octyl) are reported in pure nitrobenzene and methanol at 25, 35, and 45°C. The data were analyzed using Fuoss' equation (1980) (F-80) to obtain the three adjustable parameters; molar conductance at infinite dilution _o, association constant K_A and the association distance R that minimize the standard deviation . The variation of the parameters for each solvent are discussed with the variation of both cationic and anionic size as well as with temperature. It was found that the solvent-separated ion pair model (SSIP) can be applied in methanol for the salts under investigation. The thermodynamic parameters related to ion-pair formation were calculated and interpreted. The plots of #x039B;_o vs. the reciprocal of the molecular weight M were used to separate the molar conductances into values for the individual ions.     

Viscosities for Binary Mixtures of 1-Decanol, Hexane, and Diethylamine at 10, 25, and 40°C

Experimental viscosities provide information on the structure of liquids and are required in the design of processes, which involve fluid flow, mass transfer, or heat transfer calculations. This work reports experimental viscosity data of the binary mixtures: 1-decanol + hexane, 1-decanol + diethylamine, and hexane + diethylamine at 10, 25, and 40°C and atmospheric pressure for the whole range of compositions. The viscosities of the pure liquids and their mixtures were determined using Cannon Fenske viscometers thermostated at ±0.01°C. The estimated error in the measured viscosities was less than ±0.005 mPa-s. The dynamic viscosity and the excess energy of activation for viscous flow were also calculated. The equation of Redlich–Kister was used for fitting the excess properties of the binary mixtures. The excess viscosity shows positive deviations from ideal behavior for the mixtures 1- decanol + hexane and 1-decanol + diethylamine and a small negative deviation for the binary system hexane + diethylamine. The experimental results have been also used to test some empirical and semiempirical equations adopted previously to correlate viscosity composition data.     

Viscosities and Densities of Solutions of n-Decane, or n-Tetradecane with Several Esters at 25°C

Viscosity and density data are reported for n-decane + propyl ethanoate, propyl propanoate, propyl butyrate, and n-tetradecane + propyl ethanoate, propyl propanoate, and propyl butyrate at 25°C and atmospheric pressure. Kinematic viscosities were determined using a capillary viscosimeter and densities were measured using vibrating-tube densimetry. The equations of Grunberg–Nissan, McAllister, Auslander, and Teja were fitted to the viscosity data. Excess molar Gibbs free energies of activation for flow were also evaluated. The experimental values obtained for excess volumes were compared with the Nitta et al. group contribution model.     

Kinematic viscosities of ternary mixtures containing ethane-1,2-diol, 2-methoxyethanol and water from −10°C to 80°C

Kinematic viscosities (ν) of the ternary ethane-1,2-diol (1)+2-methoxyethanol (2)+water (3) solvent system have been measured for 36 ternary mixtures covering the whole miscibility range expressed by the condition 0<X₁,X₂,X₃<1, at 19 temperatures in the range −10≤t (°C)≤80. The measured values have been used to test some empirical equations of the type ν=ν(t) and ν=ν(X_i), in order to provide for useful interpolation procedures to obtain calculated values in correspondence to the experimental data gaps. From the experimental data, the excess kinematic viscosities (ν^E) have been calculated. Sign and magnitude of these quantities have been discussed in terms of type and nature of specific intermolecular interactions. Furthermore, derived quantities such as thermodynamic parameters of the viscous flow (ΔG*, ΔH* and ΔS*), have been analysed on the basis of the Eyring's model. All the investigated excess mixing properties indicate the probable absence of stable three-component adducts in this ternary solvent system.     

Viscosities of Some Tetraalkylammonium and Alkali-Metal Salts in N,N-Dimethylacetamide at 25°C

The viscosities of solutions of tetrapropylammonium bromide (Pr₄NBr), tetrabutylammonium bromide (Bu₄NBr), tetrapentylammonium bromide (Pen₄NBr), tetrahexylammonium bromide (Hex₄NBr), tetraheptylammonium bromide (Hep₄NBr), tetraoctylammonium bromide (Oct₄NBr), tetrabutylammonium tetraphenylborate (Bu₄NBPh₄), sodium tetraphenylborate (NaBPh₄), and potassium tetraphenylborate (KBPh₄) in N,N-dimethylacetamide are reported at 25^°C. The viscosity data havebeen analyzed by the Jones-Dole equation for associated electrolytes to evaluate the viscosity B coefficients of the electrolytes. These data have also been analyzed by the transition-state theory to obtain the contribution of the solutes to the free energy of activation for viscous flow of the solution. The ionic contribution to the viscosity B coefficient and the free energy of activation for viscous flow have been estimated using of the reference electrolyte Bu₄NBPh₄. The bromide, tetraphenylborate, and tetraalkylammonium ions are found to be weakly solvated in N,N-dimethylacetamide, whereas significant solvation has been detected for sodium and potassium ions. The viscosity of the solvent is greatly modified by the presence of all the ions investigated here with the exception of the bromide ion.     

Voltammetric Analysis of Iodide and Diffusion Coefficients Between 25 and 85°C

The oxidation wave of iodide in 0.075 mol-L^–1 H₂SO₄ was analyzed at 25, 40, 55, 70, and 85°C. The reversibility of the I₂/I^– system was checked using logarithmic transforms, half-wave potentials, and by studying I ^–1 = f(^–1/2). The limiting currents obtained enabled us to determine the diffusion coefficient of I^– using Newman's equation. These experimental results were compared with Nernst's limiting values. The Stokes–Einstein equation is not verified. Hydration numbers for I^– at different temperatures were established. An empirical equation is proposed to predict the evolution of diffusion coefficients in a sulfuric acid medium with temperature.     

Conductivity Studies of Dilute Aqueous Solutions of Oxalic Acid and Neutral Oxalates of Sodium, Potassium, Cesium, and Ammonium from 5 to 35°C

Conductivity measurements of oxalic acid and neutral oxalates (disodium oxalate, dipotassium oxalate, dicesium, and diammonium oxalate) were performed on dilute aqueous solutions, c < 3 × 10^–3 mol-dm^–3, from 5 to 35°C. These data and those available from the literature were analyzed in terms of dissociation steps of oxalic acid, the Onsager conductivity equation for neutral oxalates, the Quint–Viallard conductivity equation for the acid, and the Debye–Hückel equation for activity coefficients, to give the limiting equivalent conductances of bioxalate anion ;(HC₂O₄ ^–) and oxalate anion (1/2C₂O₄ ^2–) and the corresponding dissociation constants K ₁ and K ₂.     

Volumetric Properties of Binary Mixtures of Acetonitrile and Chloroalkanes at 25°C and Atmospheric Pressure

Excess molar volumes for binary mixtures of acetonitrile + dichloromethane, acetonitrile + trichloromethane, and acetonitrile + tetracloromethane at 25°C have been used to calculate partial molar volumes , excess partial molar volumes , and apparent molar volumes of each component as a function of composition. The V _m ^Evalues are negative over the entire composition range for the systems studied. The applicability of the Prigogine–Flory–Patterson theory was explored. The agreement between theoretical and experimental results is satisfactory for the systems with dichloromethane and tetrachloromethane. For the unsymmetrical behavior of the system with trichloromethane, however, the agreement is poor.     

Thermodynamic and spectroscopic properties of 2-pyrrolidinones. 7. ΔE T N for binary solvent mixtures of 2-pyrrolidinone andN-methylbenzenesulfonamide at 30 and 50°C

ΔE _T ^N values for 2-pyrrolidinone and N-methylbenzenesulfonamide solvent systems, in which the solvents were benzyl alcohol, 1,4-dioxane and hexamethylphosphoric triamide, were determined over the whole mole fraction range. The study was carried out at 30 and 50°C. The ΔE _T ^N values were positive for all of these systems, with the exception of the 2-pyrrolidinone-hexamethylphosphoric triamide system, which was slightly negative. The results are discussed in terms of intermolecular interactions and preferential solvation.     

Excess Molar Volumes and Viscosities of Binary Mixtures of Methanol and the Ionic Liquid 4-Methyl-N-butylpyridinium Tetrafluoroborate at 25, 40, and 50°C

Experimental data of densities and viscosities are presented for the system 4-methyl-N-butylpyridinium tetrafluoroborate + methanol at 25, 40, and 50, 323.15 K and ambient pressure using a vibratage-tube densimeter and an Ubbelohde viscometer. Excess molar volumes V ^E and excess logarithm viscosities (ln )^E have been determined. V ^E is negative and (ln )^E positive over the entire mixture composition.     

Solubility of light fullerenes in oleic, linoleic, and linolenic acids at 20–80°C

Solubility of light fullerenes (C₆₀, C₇₀, and the standard fullerene mixture containing (wt %): C₆₀ 65, C₇₀ 34, C _n>70 1) in the oleic, linoleic and linolenic acids, respectively, at 20–80°C was studied and the corresponding solubility polytherms were reported.     

Isopiestic Determination of Osmotic and Activity Coefficients for Solutions of LiCl, LiBr, and LiNO3 in 2-Propanol at 25°C

The osmotic coefficients of lithium chloride, lithium bromide, and lithium nitrate in 2-propanol have been measured by the isopiestic method at 25^°C. Sodium iodide was used as the isopiestic standard. The molality ranges covered were from 0.2 to 1.5 for LiCl and LiBr, and to 1.9 mol-kg^-1 for LiNO₃. The system of equations developed by Clegg–Pitzer and Pitzer were used to fit each set of osmotic coefficients. The experimental osmotic coefficient data are successfully correlated with these models. The parameters from the fit were used to calculate the mean molal activity coefficients.     

Apparent molar and partial molar volumes of aqueous ceric ammonium nitrate solutions at 20, 25, 30, and 35°C

Present paper reports the measured densities (ρ) and refractive indices (n _D) of aqueous solutions of ceric ammonium nitrate (CAN) at 20, 25, 30, and 35°C in different concentrations of solution. Apparent molar volumes (φ_v) have been calculated from the density data at different temperatures and fitted to Massons relation to get limiting partial molar volumes (? _v ⁰ ) of CAN. Refractive index data were fitted to linear dependence over concentration of solutions and values of constant K and n _D ⁰ for different temperatures were evaluated. Specific refractions (R _D) of solutions were calculated from the refractive index and density data. Concentration and temperature effects on experimental and derived properties have been discussed in terms of structural interactions.     

Influence of aluminium on the oxidation of titanium between 550 and 750 °C

In order to study the influence of aluminium on the oxidation resistance of titanium at high temperature, a range of binary alloys containing 1.65, 3, 5 and 10 wt.% of aluminium was prepared. Their oxidation kinetics were studied at temperatures between 500 and 750 °C using either continuous thermogravimetry or daily weighing for periods of up to several thousand hours. The results obtained for oxidation in air confirm the beneficial role of aluminium which has been observed previously for oxidation in oxygen. With regard to morphology and structure, aluminium modifies the internal structure of the oxide layers and their growth laws. A general dispersion of aluminium in rutile is observed, although a concentration of this phase is noted near the external interface; there is also a reduction in the amount of oxygen dissolved in the metal substrate which is related to the aluminium content in the alloy. Moreover, the presence of aluminium also modifies the adhesion of the oxide layers to the substrate.     

Excess Molar Volumes of Binary Mixtures of Hexanol and Polyethers at 25°C

Excess molar volumes V_m^E at 25°C and atmospheric pressure over the entire composition range for binary mixtures of 1-hexanol with n-polyethers: 2,5-dioxahexane, 3,6-dioxaoctane, 2,5,8-trioxanonane, 3,6,9-trioxaundecane, 5,8,11-trioxapentadecane, 2,5,8,11-tetraoxadodecane, and 2,5,8,11,14-pentaoxapentadecane are reported from densities measured with a vibrating-tube densimeter. Systems containing 2,5-dioxahexane, 2,5,8-trioxanonane, 2,5,8,11-tetraoxadodecane or 2,5,8,11,14-pentaoxapentadecane are characterized by V_m^E > 0, probably due to predominant positive contributions to V_m^E from the disruption of H bonds of 1-hexanol and to physical interactions. In contrast, mixtures with 3,6-dioxaoctane, 3,6,9-trioxaundecane, and 5,8,11-trioxapentadecane are characterized by V_m^E < 0, indicating that the negative contribution to V_m^E from interstitial accommodation is more important.     

13C NMR of 2,3,14-Trisubstituted Δ4,7-6-Ketosteroids and Related Compounds

¹³ Spectra have been studied and signals of C atoms assigned for steroids 3-5 and 7-10, which are close structural analogs of the natural ecdysteroids 4-dehydroecdysterone 1, diaulusterol A 2, and 5,20-dihydroxyecdysone 6