The dissociation quotients of formic acid in sodium chloride solutions to 200°C

The dissociation quotients of formic acid were measured potentiometrically from 25 to 200°C in NaCl solutions at ionic strengths of 0.1, 0.3 1.0, 3.0, and 5.0 mol-kg^–1. The experiments were carried out in a concentration cell with hydrogen electrodes. The resulting molal acid dissociation quotients for formic acid, as well as a set of infinite dilution literature values and a calorimetrically-determined enthalpy of reaction, were fitted by an empirical equation involving an extended Debye Hückel term and seven adjustable parameters involving functions of temperature and ionic strength. This regressional analysis yielded the following thermodynamic quantities for 25°C: logK=–3.755±0.002, H^o=–0.09±0.15 kJ-mol^–1, S^o=–72.2±0.5 J-K^–1-mol^–1, and C _p ^o =–147±4 J-K^–1-mol^–1. The isocoulombic form of the equilibrium constant is recommended for extrapolation to higher temperatures.     

Standard enthalpies of formation of γ-aminobutyric acid and the products of its dissociation in aqueous solution

Heat effects of the dissolution of crystalline γ-aminobutyric acid in water and potassium hydroxide solutions are determined by direct colorimetry at 298.15 K. Standard enthalpies of formation of γ-aminobutyric acid and the products of its dissociation in aqueous solution are calculated.     

Standard enthalpies of formation of α-aminobutyric acid and products of its dissociation in an aqueous solution

Heats of solution of crystalline α-aminobutyric acid in water and in aqueous solutions of potassium hydroxide at 298.15 K are measured by means of direct calorimetry. Standard enthalpies of formation of the amino acid and products of its dissociation in an aqueous solution are calculated.     

Thermodynamic and acoustic properties of binary mixtures of PEGDME 250 with 1-propanol and 1-butanol at 293, 303 and 313°K

ABSTRACT

The work presented in this paper deals with the study of thermodynamic properties of new working fluids for absorption machines, mainly for characterisation of absorbent–refrigerant pairs that could improve the cycle performance. The study of atomic motion in liquids plays an important role in understanding the solid-like behaviour of liquids. The accurate measurement of the energy changes due to scattering can be used to study the dynamical behaviour of liquids. Measurements of the ultrasonic velocity (u), density (ρ) and viscosity (η) for binary mixtures of polyethylene glycol 250 dimethyl ether with 1-propanol and 1-butanol have been made at three temperatures (T = 293, 303 and 313 K) over the entire composition range in order to investigate the nature of intermolecular interactions between the components of these liquid mixtures. Non-linear variation of derived quantities with the mole fraction supports the molecular interaction occurring between component molecules.     

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.     

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.     

Thermodynamic properties and amorphization of Zr–Si melts

The relationship between the thermodynamic properties of Zr–Si liquid alloys and their propensity to amorphization is studied. The temperature–concentration dependences of the thermodynamic properties of melts are presented using the concept of associated solutions. It is shown that the range of amorphization coincides with the range of the predominant concentration of Zr₃Si associative groups with low formation entropy.     

Ternary phase equilibria for the sodium chloride–sodium sulfate–water system at 200 and 250 bar up to 400°C

Phase equilibria in the NaCl–Na₂SO₄–H₂O system were investigated at 200 and 250 bar for total salt concentrations ranging from 5 to 20 wt.% total salt over temperatures ranging from 320 to 400°C. In addition to providing data for this ternary system, the experiments also added information on the phase behavior of the two binary systems: NaCl–H₂O and Na₂SO₄–H₂O. For salt mixture compositions which were rich in sodium sulfate, a solid phase was observed to nucleate from the homogeneous liquid phase. Salt mixture compositions which had a high fraction of sodium chloride exhibited a vapor separation from a homogeneous liquid phase. By fitting curves to the solid–liquid and vapor–liquid separation temperatures, the temperature and composition of a constrained invariant point where liquid, solid salt and vapor are in equilibrium were estimated. These estimates were performed at discrete compositions of 5, 10, 15 and 20 wt.% total salt at pressures of 200 and 250 bar. The temperature and composition of the invariant point increased with increasing pressure following a simple thermodynamic model for boiling point elevation in a nearly ideal solution.     

Oxoacidic properties of potassium halide melts at 800°C

The equilibrium CO₃²⁻ = CO₂+O²⁻ (pK) in molten potassium halides (KCl, KBr and KI) and KCl-NaCl eutectic at 800°C was investigated to compare the oxoacidic properties of the melts. A potentiometric cell involving Pt(O₂)|ZrO₂(Y₂O₃) membrane oxygen electrode was used to detect the equilibrium O²⁻ molalities. The obtained pK values were 3.2±0.2 (KCl), 2.4±0.2 (KBr), 4.4±0.2 (KI) and 3.6±0.2 (KCl-NaCl) allowing arrangement of the melts studied in the following sequence: KI–KCl-NaCl–KCl–KBr with the melt acidities increasing within 2 pI units. The oxides solubilities were found to decrease sequentially from the chloride to the iodide melt.     

p-V-T parameters of propylencarbonate and cis-,trans-decahydronaphthalene in temperature and pressure ranges of 20–50°C and 1–1000 bar

The condensability of propylencarbonate and cis-,trans-decalin (40: 60 wt %) were measured using the liquid weighting method in the temperature and pressure ranges of 20–50°C and 1–1000 bar, respectively. The Tait equation coefficients C and B for this temperature interval were calculated. Taking pro-pylencarbonate as an example, it was demonstrated that equation 1/β _T = 0.9759 × (1000V ₀/ΔV _{1 kbar}) — 4386 proposed earlier for liquids allows us to predict C and B coefficients with good precision.     

Thermodynamic properties and electrochemical behavior of lithium–germanium alloys

Published data on the phase diagram of the lithium–germanium system, on the thermodynamic properties of Li–Ge alloys, on their electrochemical behavior in various media, and on prospects for using them in lithium–ion batteries and in other chemical current sources are analyzed.     

Thermodynamic properties of tetraphenylantimony benzophenoxymate in the region of 0–450 K

Heat capacity of tetraphenylantimony benzophenoxymate Ph₄SbONCPh₂ is measured for first time using adiabatic calorimeter in the range from 6K to 350K and differential scanning calorimeter in the range from 330 K to 450 K. In the range of 400–450 K is revealed a melting accompanied with partial decomposition of the substance. Standard thermodynamic functions of crystalline Ph₄SbONCPh₂ in the range from T → 0 K to 440 K are calculated. Enthalpy of combustion of this compound is measured in a combustion calorimeter with isothermal cover and static bomb. Standard thermodynamic formation functions of crystalline Ph₄SbONCPh₂ at 298.15 K are calculated. Fractal dimension D is revealed.     

γ-ray radiolysis of dihydroxyurea in nitric acid and its radiolytic products

Journal of Radioanalytical and Nuclear Chemistry - Dihydroxyurea (DHU) is a new salt-free reducing agent applied for the separation of Pu and Np from U in spent fuel reprocessing. This paper...     

Refractivity and polarizability of mixtures of L-histidine–metformin hydrochloride–water at 30°C

The molar refractivity and polarizability of mixtures of L-histidine (0.01–0.11 mol L^–1)–metformin hydrochloride (0.03, 0.05, 0.07 mol L^–1)–water were calculated from density and refractive index data at 30°C. Enhancement in the polarizability has been observed with increase in L-histidine concentration as well as metformin hydrochloride content in the solution. The molar refractivity and polarizability of solutions increased appreciably after 0.09 mol L^–1 L-histidine in each aqueous solution.     

Thermodynamic and surface properties of Ge–Ga and Ge–Sb liquid alloys

Thermodynamic and surface properties of Ge–Ga and Ge–Sb liquid alloys have been studied using statistical mechanical formulations based on complex formation and that based on the concept of layered structure near the interface. The study showed that low level of complex formation of the form Ge _{2 Sb} exists in Ge–Sb toward the Ge-rich end of the concentration range and the surface properties of Ge–Ga are almost equal to their corresponding bulk equivalent.     

Volumetric properties of cyclic hydrocarbons in tetrachloromethane at 25°C

By means of a vibrating-tube densimeter, the densities at 25°C have been determined for binary mixtures of tetrachloromethane with a liquid (cyclodecane, cis-decahydronaphthalene, trans-decahydronaphthalene, bicyclohexyl, pentane) or a solid hydrocarbon (cyclododecane, cyclopentadecane, norbornane, adamantane, octahydro-4,7-methano-1H-indene). Excess molar volumes have been obtained in the whole mole fraction range for mixtures containing a liquid hydrocarbon. For solid cycloalkanes, apparent molar volumes have been evaluated in the whole range of miscibility. The partial molar volumes at infinite dilution have been calculated for all examined cycloalkanes and compared with those of n-alkanes. The dependence of upon the size and shape of the ring or cage structure of the solute is discussed. The capability of the Flory theory to reproduce V^E for these mixtures is also tested.     

Thermodynamic properties of binary mixtures: Hexamethylphosphoric triamide (HMPA) with a non-polar liquid at 25°C

Excess isobaric heat capacities C _p ^E , densities and speeds of sound u of HMPA+heptane and+benzene were measured at 25°C. C _p ^E of both mixtures were positive in the range of small x and negative in the other region. The mixture containing benzene showed higher C _p ^E than the heptane mixture. They both exhibited considerably smaller C _V ^E than C _p ^E . V^E was positive for HMPA+heptane and negative for HMPA+benzene. The compressibilities K _s ^E and K _p ^E of both mixtures were negative. In both mixtures, non-random mixing is expected and [(CH₃)₂N]₃PO molecules are inhomogeneously distributed.     

Measurement of Some Thermodynamic and Acoustic Properties of Binary Solutions of N,N-Dimethylformamide with 1-Alkanols at 30°C and Comparison with Theories

Densities, and ultrasonic velocities, uof binary mixtures of N,N-dimethylformamide (DMF) + methanol, + ethanol, + 1-propanol, + 1-butanol, + 1-pentanol, and + 1-hexanol have been measured at 30°C. The ultrasonic velocities have been compared with values calculated from the free-length theory ( FLT) due to Jacobson and collision-factor theory ( CFT) due to Schaaffs. The measured data are used to compute adiabatic compressibility (k _s), deviation in adiabatic compressibility (k _s), intermolecular free length (L _f), molar volume (V _m), and available volume (V _a). The excess molar volume ( V _m ^E) and excess free length (L _f ^E) are also evaluated. For all systems, these results were satisfactorily correlated by the Redlich–Kister polynomial. These parameters are used to discuss dissociation of the self-associated 1-alkanol molecules and the formation of aggregates between unlike molecules through C=O...H–O hydrogen bonding.