Activity coefficients of electrolytes from the E.M.F. of liquid membrane cells. II - multicharged electrolyte solutions

The activity coefficients of Co(en)₃Cl₃ and K₂SO₄ were measured by means of a cell with ion-exchange liquid membranes following the method described in paper I. The results prove that this method is even more valuable with multicharged salts than with 1-1 electrolytes. The values obtained are precise and reliable down to dilution limits never before accessible, e.g., 4×10^–5 mol-kg^–1 in Co(en)₃Cl₃. High dilution levels are of particular importance when dealing with highly charged electrolytes since the trend at higher concentrations often leads to errors both in extrapolation to infinite dilution and in the absolute activity coefficients. As an application, the activity coefficients of [Co(en)₃]₂(SO₄)₃-suspected to be wrongly evaluated in past literature-were measured, and their values at low concentrations were actually lower than those quoted before.     

Activity coefficients of electrolytes from the E.M.F. of liquid membrane cells. I. The method—Test measurements on KCl

A new electrochemical cell is described, in which two permselective liquid membranes, one anionic the other cationic, are interposed between the subsidiary electrodes and the solution of the electrolyte under examination By means of this kind of cell it is possible to measure activity coefficients of salts of cations and anions for which reversible electrodes are not available, with great accuracy even at high dilutions never accessible before (down to ≊10⁻⁴ mol-dm⁻³). The cell performance has been tested by measuring the activity coefficients of KCl for which accurate data are available in literature.     

The origin of the conductivity maximum in molten salts. I. Bismuth chloride

A new theory is presented to explain the conductivity maxima of molten salts (versus temperature and pressure). In the new theory, conductivity is due to ions hopping from counterion to counterion, and its temperature dependence can be explained with an ordinary Arrhenius equation in which the frequency prefactor A (for hopping opportunities) and activation energy E(a) (for hopping) are density dependent. The conductivity maximum is due to competing effects: as density decreases, the frequency of opportunities for hopping increases, but the probability that an opportunity is successfully hopped decreases due to rising E(a) caused by the increased hopping distance. The theory is successfully applied to molten bismuth (III) chloride, and supported by density-functional based molecular dynamics simulations which not only reproduce the conductivity maximum, but disprove the long-standing conjecture that this liquid features an equilibrium between BiCl(3) molecules, and BiCl(2)(+) and BiCl(4)(-) ions that shifts to the left with increasing temperature.     

Rate coefficients for the reaction of OH with a series of unsaturated alcohols between 263 and 371 K

Rate coefficients for the gas-phase reactions of OH radicals with four unsaturated alcohols, 3-methyl-3-buten-1-ol (k1), 2-buten-1-ol (k2), 2-methyl-2-propen-1-ol (k3) and 3-buten-1-ol (k4), were measured using two different techniques, a conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. The Arrhenius rate coefficients (in units of cm(3) molecule(-1) s(-1)) over the temperature range 263-371 K were determined from the kinetic data obtained as k1 = (5.5 +/- 1.0) x 10(-12) exp [(836 +/- 54)/T]; k2 = (6.9 +/- 0.9) x 10(-12) exp [(744 +/- 40)/T]; k3 = (10 +/- 1) x 10(-12) exp [(652 +/- 27)/T]; and k4 = (4.0 +/- 0.4) x 10(-12) exp [(783 +/- 32)/T]. At 298 K, the rate coefficients obtained by the two methods for each of the alcohols studied were in good agreement. The results are presented and compared with those obtained previously for the same and related reactions of OH radicals. Reactivity factors for substituent groups containing the hydroxyl group are determined. The atmospheric implications for the studied alcohols are considered briefly.     

Nitrosoalkylureas with a quaternary nitrogen. 7. Quantitative relation between decomposition rate and structure of nitrosoalkylureas derived from alkylammonium salts

Conclusions The decomposition rate of the dialkyl-substituted methyl- and cyclohexylnitrosoureas correlates well with the charge on N that does not carry the nitroso group, as calculated by CNDO/2. Here the cyclohexyl residue has a greater destabilizing effect than does the methyl radical.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 798–800, April, 1989.     

On the relation between virial coefficients and the close-packing of hard disks and hard spheres

The question of whether the known virial coefficients are enough to determine the packing fraction η(∞) at which the fluid equation of state of a hard-sphere fluid diverges is addressed. It is found that the information derived from the direct Pade? approximants to the compressibility factor constructed with the virial coefficients is inconclusive. An alternative approach is proposed which makes use of the same virial coefficients and of the equation of state in a form where the packing fraction is explicitly given as a function of the pressure. The results of this approach both for hard-disk and hard-sphere fluids, which can straightforwardly accommodate higher virial coefficients when available, lends support to the conjecture that η(∞) is equal to the maximum packing fraction corresponding to an ordered crystalline structure.     

Empirical approximations of the thermal E.M.F.-temperature dependence for the standard thermocouple 90 pt-10 Rh/Pt

Thermal e.m.f. as a function of temperature for the standard thermocouple 90 Pt-10 Rh/Pt is very well approximated by functions of the type t.e.m.f.=At ^B, Which can be easily inverted.     

Room temperature solution studies of complexation between o-chloranil and a series of anilines by spectrophotometric method.

Electron donor-acceptor (EDA) complex formation between o-chloranil and a series of anilines has been studied in CCl4 medium. In all the cases, EDA complexes are formed instantaneously on mixing the donor and acceptor solutions. N,N-dimethylaniline and N,N-dimethyl-p-toluidine form stable EDA complexes with o-chloranil while the other complexes decay slowly into secondary products. The kinetics of all these reactions has been studied by UV-VIS absorption spectrophotometric method and the rate constants of the reactions and formation constants of the EDA complexes have been determined. The charge transfer (CT) transition energies of the complexes are found to change systematically with change in the number and position of the methyl groups in the donor molecules (methylanilines). From an analysis of this variation, the electron affinity of o-chloranil has been found to be 2.54 eV. A perturbational inductive effect Hückel parameter hMe has been found from this trend and the value obtained (-0.27) is very close to that (-0.3) obtained by Lepley (J. Am. Chem. Soc., 86 (1964) 2545) from a study of tetracyano ethylene (TCNE)-methylbenzene complexes.     

Room temperature rate coefficient for the reaction between CH3O2 and NO3

The molecular modulation spectroscopic technique was employed to study the kinetics of NO₃ radicals produced in the 253.7 nm photolysis of flowing gas mixtures of HNO₃/CH₄/O₂ at room temperature. By computer fitting of the NO₃ temporal behavior, a rate coefficient of (2.3 ± 0.7) × 10^?12 cm³ molecule^?1 s^?1 was obtained for the reaction between NO₃ and CH₃O₂ at 298 K.     

Interaction between nuclear graphite and molten fluoride salts: a synchrotron radiation study of the substitution of graphitic hydrogen by fluoride ion

The interaction between nuclear graphite and molten fluoride salts (46.5 mol % LiF/11.5 mol % NaF/42 mol % KF) is investigated by synchrotron X-ray diffraction and C K-edge X-ray absorption near-edge structure (XANES). It is found that there are a large number of H atoms in IG-110 nuclear graphite, which is attributed to the residual C-H bond after the graphitization process of petroleum coke and pitch binder. The elastic recoil detection analysis indicates that H atoms are uniformly distributed in IG-110 nuclear graphite, in excellent agreement with the XANES results. The XANES results indicate that the immersion in molten fluoride salts at 500 °C led to H atoms in nuclear graphite partly substituted by the fluorine from fluoride salts to form C-F bond. The implications of these findings are discussed.     

Surface tension and its temperature coefficient of molten tin determined with the sessile drop method at different oxygen partial pressures

The surface tension of molten tin has been determined by the sessile drop method at temperatures ranging from 523 to 1033 K and in the oxygen partial pressure (P(O(2))) range from 2.85 x 10(-19) to 8.56 x 10(-6) MPa, and its dependence on temperature and oxygen partial pressure has been analyzed. At P(O(2))=2.85 x 10(-19) and 1.06 x 10(-15) MPa, the surface tension decreases linearly with the increase of temperature and its temperature coefficients are -0.151 and -0.094 mN m(-1) K(-1), respectively. However, at high P(O(2)) (3.17 x 10(-10), 8.56 x 10(-6) MPa), the surface tension increases with the temperature near the melting point (505 K) and decreases above 723 K. The surface tension decrease with increasing P(O(2)) is much larger near the melting point than at temperatures above 823 K. The contact angle between the molten tin and the alumina substrate is 158-173 degrees, and the wettability is poor.     

Remarks on the relationship between isothermal and non-isothermal kinetic results. A new method for the kinetic analysis of isothermal data

Addition of 10mg/l of the haevy metal ions Zn⁺⁺, Cu⁺⁺, Pb⁺⁺, Cd⁺⁺ and Cr⁺⁺ to nongrowing E.coli cells shows a decrease in heat production by aerobic and anaerobic glycolysis up to 80 %. The heat production of cells incubated without glucose was decreased drastically too, after addition of 10mg/l of these heavy metal ions.The pattern of heat released during active transport of α MG was influenced by these haevy metal ions in a way, that there was a decrease in maximum heat flow, whereas the total heat production seemed to be constant.After increasing the metal ion concentration up to 100mg/l no endogenous heat production could be detected. The inhibition of heat production after addition of glucose was higher than 90 % in this case and there was a strong inhibition in α MG uptake.The results of these investigations indicate that the basic action of all tested metal ions is the energy metabolism and not the transport as stated earlier.     

On the relation between the activation energy for electron attachment reactions and the size of their thermal rate coefficients

Rate coefficients k(T) for dissociative electron attachment (DEA) to molecules in many cases exhibit a more or less strong rise with increasing temperature T (the electron temperature T(e) and the molecular temperature T(G) are assumed to be in thermal equilibrium, i.e., T = T(e) = T(G)). This rise is frequently modeled by the Arrhenius equation k(T) = k(A) exp[-E(a)∕(k(B)T)], and an activation energy E(a) is deduced from fits to the experimental data k(T). This behavior reflects the presence of an energy barrier for the anion on its path to the dissociated products. In a recent paper [J. Kopyra, J. Wnorowska, M. Forys?, and I. Szamrej, Int. J. Mass Spectrom. 268, 60 (2007)] it was suggested that the size of the rate coefficients for DEA reactions at room temperature exhibits an exponential dependence on the activation energy, i.e., k(E(a); T ≈ 300 K) = k(1) exp[-E(a)∕E(0)]. More recent experimental data for molecules with high barriers [T. M. Miller, J. F. Friedman, L. C. Schaffer, and A. A. Viggiano, J. Chem. Phys. 131, 084302 (2009)] are compatible with such a correlation. We investigate the validity and the possible origin of this dependence by analyzing the results of R-matrix calculations for temperature-dependent rate coefficients of exothermic DEA processes with intermediate barrier toward dissociation. These include results for model systems with systematically varied barrier height as well as results of molecule-specific calculations for CH(3)Cl, CH(3)Br, CF(3)Cl, and CH(2)Cl(2) (activation energies above 0.2 eV) involving appropriate molecular parameters. A comparison of the experimental and theoretical results for the considered class of molecules (halogenated alkanes) supports the idea that the exponential dependence of k(T = 300 K) on the activation energy reflects a general phenomenon associated with Franck-Condon factors for getting from the initial neutral vibrational levels to the dissociating final anion state in a direct DEA process. Cases are discussed for which the proposed relation does not apply.     

The control of the temperature and the feed in deactivating isothermal catalyst beds

A comparison of the space time policy and the temperature policy to be followed in order to maintain a constant outlet conversion in spite of catalystGraphic design charts which allow the catalyst lifetime and the production for a given conversion rate to be determined are presented for both strategiFinally, catalyst lifetime and production values obtained following these policies are compared.