Effect of solvent on the partial molal volumes and heat capacities of nonelectrolytes

Group contributions to in seven solvents and to in three solvents have been tabulated. The variation of group parameters is discussed in terms of the solvent compressibility coefficient, _T. The scaled particle theory (SPT) is used to calculate cavity contributions to and C _p2 ^o . Interaction contributions are obtained from the cavity terms and and values estimated through the additivity schemes. values are more sensitive to solute-solvent interactions than in water and less sensitive in methanol. The SPT results for heat capacities support the concept of structural promotion by hydrophobic solutes in water.     

Partial molal heat capacities of aqueous tetraalkylammonium bromides as functions of temperature

Enthalpies of solution have been measured from 5 to 85°C for aqueous tetraethyl- and tetrapropylammonium bromides, and the integral heat method is employed to evaluate for these electrolytes over a wide temperature range. Data taken from the literature have been used to evaluate for aqueous Bu₄NBr over a similar temperature range. These data, along with similar data for Me₄NBr, previously reported, have been used to evaluate absolute ionic heat capacities. While the absolute values agree only qualitatively with two other methods of division, the temperature dependences of the three methods essentially agree up to 65°C. Heat capacities due to structural effects on the solvent, obtained by subtracting the inherent heat capacities of the ions, are extraordinarily positive for all four tetraalkylammonium ions and have negative temperature coefficients, indicating that all four ions, including the tetramethylammonium ion, are structure-making ions.     

Deficiencies of the ferricinium-ferrocene redox couple for estimating transfer energies of single ions

The difference between the partial molal entropies of ferrocene and ferricinium has been determined in nine solvents from the temperature dependence of the formal potential of the ferricinium-ferrocene redox couple using a nonisothermal electrochemical cell arrangement in order to probe possible structural reasons for the limitations of the ferrocene assumption for estimating the transfer thermodynamics of single ions between different solvents. In contrast to the uniformly small positive values of predicted by the Born model, the experimental quantities varied widely from small or even negative values in hydrogen-bonded solvents (–5 to 3 e.u.) to substantially larger values (11–14 e.u.) in dipolar aprotic media. These variations appear to arise chiefly from additional solvent ordering in the vicinity of the ferricinium cation compared to the ferrocene molecule which is enhanced in the aprotic solvents. The variations in between water and a number of nonaqueous solvents provide a predominate contribution to the differences between the free energies of single ion transfer calculated using the ferrocene and alternative extrathermodynamic assumptions.     

Thermodynamic properties of organic compounds in aqueous solution. II. Apparent molal heat capacities of piperidines,morpholines, and piperazines

Apparent molal heat capacities of some piperidine, morpholine, and piperazine derivatives in aqueous solution have been determined by adiabatic calorimetry in the temperature range 20–55°C and in the molality range 0.2–1m. Comparison of experimental values with those calculated through group contributions, found for monofunctional compounds, indicates strong interactions between the hydrophilic centers. An interpretation is given of the possible mechanism of this interaction. Also, values of ΔC _p for the addition reaction of proton to nitrogen centers of mono- and bifunctional organic compounds are examined.     

Heat capacity changes for the lonization of aqueous phenols at 25°C

The apparent molal heat capacities have been determined at 25°C for phenol,meta-nitrophenol,para-nitrophenol,meta-cyanophenol, andpara-cyanophenol and the corresponding sodium salts in water at several concentrations. These values have been extrapolated to infinite dilution to provide the values from which the heat capacity changes for the ionization of the aqueous phenols have been calculated. The observed values are virtually identical within experimental error for the phenols studied. The volume data needed to calculate the values from the experimental data are also reported.To whom correspondence should be addressed.     

Effect of charge on the standard partial molar volumes and heat capacities of organic electrolytes in methanol and water

Previously developed additivity schemes for nonelectrolytes have been used to estimate and for tetraalkyl and tetraphenyl methanes in methanol and water. Corrections have been applied to the thermodynamic values of these model compounds to account for a variation in size of the central atom, and these were used to ascertain the effect of charge on and of alkyl and phenyl quaternary ions having N, P and B as central atoms. Investigations of R₄NBr, (R=methyl to heptyl) salts show that the charge effect on and of R₄N⁺ ions is large and relatively independent of ion size suggesting that the solvent molecules penetrate the ions. The ability to estimate and of the quaternary ions in the bromide salt solutions has made it possible to make ionic assignments with some confidence; (Br^–) has been evaluated as 19.7±2 and 30.2±7 cm³-mol^–1 and (Br^–) as –83±7 and –68±30 J-K^–1-mol^–1 in methanol and water, respectively. The use of organic ions for making ionic assignments of and is critically examined and comparisons with other assignments are made. The scaled particle theory is employed to divide the heat capacities of electrolytes into cavity and interaction contributions.     

The effect of pressure on the ionization of water at various temperatures from molal-volume data1

The apparent molal volumes of dilute (0.002 to 1.0m) aqueous HCl and NaOH solutions have been determined at 0, 25, and 50°C and NaCl solutions at 50°C. The partial molal volumes ( ) of HCl, NaOH, and NaCl solutions have been determined from these apparent molal volumes and other reliable data from the literature. The partial-molal-volume changes ( ) for the ionization of water, H₂OH⁺+OH^–, have been determined from 0 to 50°C and 0 to 1m ionic strength from the partial molal volumes of HCl, NaOH, NaCl, and H₂O. The partial molal compressibilities ( for HCl, NaOH, NaCl, and H₂O have been estimated from data in the literature and used to determine the partial molal compressibility changes ( ) for the ionization of water from 0 to 50°C and 0 to 1m ionic strength. The effect of pressure on the ionization constant of water has been estimated from partial-molal-volume and compressibility changes using the relation from 0 to 50°C and 0 to 2000 bars. The results agree very well with the directly measured values.Contribution Number 1548 from the University of Miami.     

Systematics of nuclear charge distribution in fission the ZP model

An extension of the conventional Z_P model has been used with data for ten fission reactions and the method of least-squares for derivation of parameters that describe the nuclear charge-distributions. Data for light and heavy fission products for each reaction were treated together by consideration of the complementarity of average mass numbers of precursors (A′_L+A′_H=A_F). This treatment gave calculated yields that are essentially equal for complementary elements (Z_L+Z_H=Z_F). The parameters determined, , the Gaussian dispersion width parameter, a linear function of Δ_Z=|Z_P-A′(Z_F/A_F)|, Z_P being the Z at maximum of the curve, and and , the even-odd proton and neutron yield enhancement factors, represented most data (A_H⋟130–150 and the complementary light A's) moderately well, better than did oscillating functions of and Δ_Z. The values were found to be approximately constant (0.48 to 0.62) and, generally, to increase with the average number of neutrons emitted, . The Δ_Z values at A′=140 were in the range of 0.42 to 0.50, and the slopes, ∂Δ_Z/∂A′_H, ranged from 0.0 to 0.03. The factor was found to be several times larger than the factor and to decrease with increasing excitation energy and with A and/or Z of the fissioning nucleus, as has been reported previously. The adequacy of the Z_P model for representation of data and for prediction of yields in the high-yield mass-number regions mentioned above are discussed, and the large uncertainties that are involved in extrapolating the model to near symmetric or to very asymmetric mass and charge divisions are pointed out.     

Dynamics of H+O2 collisions on anab initio potential energy surface

The dynamics of elementary rate processes for H+O₂ collisions on an ab initio potential energy surface have been simulated by quasiclassical trajectory theory (QCT). For H+O₂ (v=0,j=1), we have obtained the reaction probabilityP _r (E,b) as a function of collision energy E and impact parameterb, the reaction cross sectionS _r as a function ofE, and the average values of the product quantum numbers of OH.For H+0₂ (v=2,j=1, 20, 40, 60, 80, 100;v=1, 3, 4, 5,j=1) atE=0.3 eV, we have found thatb _max is about 4.5a ₀ and the impact parameter at whichP _r is maximum decreases asj increases. The reaction cross section increases asj andv become large. For inelastic collisions, whenb is small andj is large, the and are both small. For reactive collisions, almost equals zero, but the probability of being larger than zero increases with increasingj; and¯v _OH even shows population inversion forj=100. Additional details of the dynamics are shown in figures of interparticle distance and stereographs.     

Preferential solvation in three component systems: Evaluation of Kirkwood-Buff parameters

The extent of local excess or deficiency of a component solvent near the solute in a mixed binary solvent has been calculated using the Hall formalism for the Kirkwood-Buff equation. The possibility of calculation of the two solute-solvent Kirkwood-Buff parameters using the values is discussed. A model calculation using literature data for preferential solvation in mixed binary solvents is presented. The solute-solvent and solvent-solvent interactions and the relative size of the solvents are also shown to be relevant factors in determining the values.     

Potentiometric investigation of NaSO 4 − ion pair formation in NaClO4 medium

The ion pair formation of NaSO ₄ ⁻ has been investigated potentiometrically in 1M NaClO ₄ medium at 25°C using two different sodium-selective indicator electrodes and a perchlorate reference electrode. The stability constant of NaSO ₄ ⁻ obtained in this study was . Although is small, it lowers the free sulfate concentration drastically in 1M NaClO ₄ medium and is a factor which should be considered in the use of NaClO ₄ as inert supporting electrolyte.     

Nonisothermal membrane phenomena across perfluorosulfonic acid-type membranes,Flemion S: Part II. Thermal membrane potential and transported entropy of ions

Thermal membrane potentials across the perfluorosulfonic acid-type membrane, Flemion S, were measured for HCl, alkali metal chlorides, and ammonium and methyl ammonium chlorides. The difference between the mean molar transported entropy of the counterions in the membrane and the partial molar entropy of the counterions in the external solution was determined from the experimental data on thermal membrane potential, thermoosmosis and electroosmosis. The sign of the thermal membrane potential in HCl solution varies from positive to negative with the concentration. In HCl and alkali metal chloride solutions, the order of their thermal membrane potentials (–/T) is H⁺>Li⁺=Na⁺>K⁺ which is roughly the inverse of that of the crystallographic radii of the ions. However, the order of their entropy differences is H⁺>Na⁺>K⁺>Li⁺ which is just the inverse of that of their thermoosmotic coefficients (D) or the entropy difference of water in thermoosmosis. For the ammonium and methyl ammonium ion forms, the orders of both –/T and increase with an increasing number of methyl groups: (CH₃)₄N⁺>(CH₃)₃NH⁺>(CH₃)₂NH ₂ ⁺ > CH₃NH ₃ ⁺ >NH ₄ ⁺ , which is also the inverse of that ofD or .     

Partial molar heat capacities of selected electrolytes and benzene in methanol and dimethylsulfoxide at 25, 40, and 80°C

A high temperature-high pressure flow heat capacity calorimeter, designed to operate to 350°C and 20 Mpa, has been constructed and tested with aqueous sodium chloride solutions to 80°C. The calorimeter has been used to measure the specific heats for solutions of NaBr, NaClO₄, ₄PBR, NaB₄, and benzene in methanol (MeOH) and dimethylsulfoxide (DMSO) at 40 and 80°C. A commercial calorimeter was used to measure the same systems at 25°C. Apparent molar heat capacities C>_p, have been evaluated and extrapolated to infinite dilution to obtain standard partial molar heat capacities . For electrolytes are positive and insensitive to temperature to 80°C in DMSO, but in MeOH, C _{p, 2} ⁰ for simple electrolytes are negative and become increasingly negative with temperature. The behavior in MeOH is attributed to strong electrostriction by ionic charge and solvation of anions by MeOH molecules which increases with temperature. This is similar to observed behavior of electrolytes in water above 100°C. For benzene is positive in MeOH and DMSO, and increases with temperature.     

Reaction graphs and a construction of reaction networks

Summary A general definition of reaction graphs is presented. For a pair of isomeric molecular graphs and , related by a chemical transformation , the reaction graph is determined using a maximal common subgraph defined for vertex mapping . A binary operation defined for graphs constructed over the same vertex set enables us to decompose the reaction graph into the sum of prototype reaction graphs. A decomposition of an overall reaction graph can be advantageously used for the construction of a reaction network. An oriented path in this network beginning at and ending at corresponds to a breakdown of the transformation into a sequence of intermediates.     

Kinetics and mechanism of the branched chain decomposition of nitrogen trichloride in the gas phase and chemical oscillations in this process

Numerical simulations of the oscillating regimes of the nitrogen trichloride self-ignition in a closed volume are carried out using a one-dimensional system of ordinary differential equations (ODE). It is shown that the suggested mechanism agrees with the experimental data. To find a solution that allows oscillations, it is sufficient to take into account (a) NC1₃ adsorption and desorption on reactor walls, (b) nonlinear chain termination , and (c) energetic chain branching . The assumption that NC1₃ desorption from the reactor surface takes place during oscillations and changes the properties of the reactor surface leads to oscillation regimes in simulation, which agrees qualitatively with the experiment.     

Oscillatory variation in yields of I2 and the reactivity of γ-irradiated TiO2 in KI solution

The reactivity of preheated and -irradiated TiO₂ was observed in KI solution by studying the kinetics of liberation of I₂. The rate of the reaction was found to be low. species proposed on the surface of oxide probably dissociate into . surface sites which oxidize I^– ions to produce free I₂. During irradiation and are produced which are reducing in nature and therefore very low yields of I₂ are observed for low -doses. In further irradiation the reformation of –O–O–, peroxy linkages is proposed hence the observed higher yields. All the processes ultimately lead to an oscillatory variation in yields of I₂ with -doses.     

Apparent molal volumes and adiabatic compressibilities of ethylene glycol derivatives in water at 5, 25, and 45°C

Density and ultrasonic velocity measurements were made on a series of dilute equeous solutions of H(OCH ₂ CH ₂ )_nOH, CH ₃ (OCH ₂ CH ₂ )_nOCH ₃ , H(CH ₂ )_nOCH ₂ CH ₂ OH (n=1–4), and poly(ethylene glycol) at 5, 25, and 45°C. The additivity of the limiting partial molal volumes ( ) and adiabatic compressibilities ( ) for CH ₂ and CH ₂ CH ₂ O groups was tested by using the observed and values of the solutes. The and values of the CH ₃ , CH ₂ , CH ₂ CH ₂ O, and CH ₂ OH groups were estimated and discussed in relation to hydration effects. The and values of alkoxyethanols calculated on the basis of the additivity of the group partial molal quantities were in good agreement with the observed values. The behavior of the limiting partial molal isothermal compressibility of alkoxyethanols was similar to that of the adiabatic compressibility.     

Dissociation Constants of Protonated Cysteine Species in NaCl Media

The sulfur-containing biomolecule, cysteine has a role in physiological and natural environment because of its strong interactions with metals. To understand these interactions of metals with cysteine, one needs reliable dissociation constants for the protonated cysteine species [ CH(CH₂SH)COOH; H₃B⁺]. The values of dissociated constants, p , for protonated cysteine species (H₃B⁺ H⁺ + H₂B, K ₁; H₂B H⁺ + HB^–,K ₂; HB^– H⁺ + B^2–,K ₃) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.5–6.0 mol-(kgH₂O)^–1 and between 5, and 45°C. The equations

Analysis of the stages of the equilibrium interaction of 2,4,6-trinitrohalobenzenes with 4-[4-(dimethylamino)styryl]pyridine as a model for activated nucleophilic substitution

A quantitative analysis was carried out on the rate and equilibrium constants of the stages of reversible activated nucleophilic substitution: σ-ionogens σ-ion pair ⇄ free ions L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg St., 340114 Donetsk, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 2, pp. 72–74, March–April, 1997.     

First and second thermodynamic mixing functions of ethylbenzene+n-nonane, +n-decane,and+n-dodecane at 25 and 45°C

Isothermal compressibilities _T and isobaric thermal expansion coefficients _p have been determined for mixtures of ethylbenzene+n-nonane, +n-decane, and +n-dodecane at 25 and 45°C in the whole range of composition. The excess functions and have been obtained at each measured mole fraction. The first one is zero for ethylbenzene +n-nonane, positive for ethylbenzene +n-decane, and +n-dodecane and increases with chain length n of the n-alkane. The function is positive for the three studied systems and nearly constant with n. Both mixing functions increase slightly with temperature. From this measurement and supplementary literature data of molar heat capacities at constant pressure C _P , the isentropic compressibilities _S, the molar heat capacities at constant volume C _V and the corresponding mixing functions have been calculated at 25°C. Furthermore, the pressure dependence of excess enthalpy H ^B , at zero pressure and at 25°C has been obtained from our experimental results of and experimental literature values for excess volume V ^E .