AbstractInfluence of thermodynamic data errors upon the results of calculation of equilibrium composition of complex chemically reacting systems is examined. Two possible approaches (sensitivity analysis and statistical approach) are described. The examples showing significance of the error influence are presented.

AbstractThe molar volume and density of pure toluene has been determined from 323 K to 673 K and from 5 to 300 MPa. An autoclave is described which has a variable internal sample volume. 16 different constant volumes have been used and with stepwise increasing temperatures, pairs of temperature and pressure values have been taken along isochors. For the pressure range of 5 to 300 MPa and for 8 isotherms a Tait equation of state is adapted and the calculated data are given. The Tait parameters are presented. The average deviation between experimental and calculated data is below 0.15%. Up to 100 MPa, comparison with recent NIST calculations and other literature data is made. The data are in good agreement.

AbstractReactions of 2‐butoxy radicals have been investigated using time‐resolved measurements of NO2 and OH concentration profiles in the flash initiated oxidation of 2‐bromobutane and subsequent numerical simulation. 2‐butoxy radicals were produced selectively by the excimer‐laser photolysis of 2‐bromobutane at 193 or 248 nm followed by the reaction of 2‐butyl radicals with O2 and NO. Whereas NO2 was detected by cw‐LIF, detection of OH was achieved by laser long‐path absorption at 308 nm. All experiments were performed at 293 K and a total pressure of 50 mbar. The rate coefficients of the O2 reaction (kO2) and of unimolecular decomposition (kdecomp) have been varied, using the FACSIMILE code, until best fits were obtained. The following rate coefficients were derived: kO2 = (6.5±2) × 10−15 cm3‐molecule−1·s−1 and kdecomp = (3.5±2) × 10−3 s−1.

AbstractResults of first‐principles, density‐functional LMTO‐ASA calculations on the two title compounds and of unrestricted Hartree‐Fock (UHF) calculations on VF2 are reported. The calculations on the crystalline materials were performed with special emphasis on optimising all (three) structural parameters, on the valence density of states and the valence electron density, and on the possible existence of spin polarisation. In addition, full‐potential LMTO calculations on isolated monomers were carried through in order to examine the nearest‐neighbour (TiO and VF) chemical bonds in detail and to understand the consequences of various approximations in describing the potential for the crystal. The LMTO‐ASA calculations reproduce the correct lattice constants with, however, some overestimate for VF2. Also the nearest‐neighbour TiO and VF bond lengths are reproduced correctly by the LMTO calculations, whereas the c/a ratios are significantly overestimated. By analysing the charge densities of the isolated monomers we conclude that the overestimates in the c/a ratios are due to the ASA (Atomic‐Sphere Approximation), which does not describe the quadrupole‐quadrupole interactions of the compounds sufficiently accurately. The Hartree‐Fock calculations yield lattice constants for VF2 very close to experiment. Also in agreement with experiment, TiO2 is found to be non‐magnetic and insulating/semiconducting. In contrast, VF2 is found to be metallic within the LMTO‐ASA method, although the density‐functional calculations indicate that magnetic effects will change the compound into an insulator as it is according to experiment. On the other hand, in agreement with experimental evidence, UHF yields a non‐metallic structure. It further shows the stability of a number of patterns of magnetic ordering.

AbstractThe influence of the viscosity contrast factor A [( = η“‐η′)/(η“+η), η, shear viscosity: (′)(”), indices of the coexisting phases; η“>η′]on the formation of viscous fingers at a mechanically unstable liquid/liquid interface of mixtures with a miscibility gap in a narrow rectangular glass cell (closed Hele‐Shaw cell) is studied. The systems used for the experiments are: (a) 2‐butoxyethanol (C4E1)/water mixtures of critical composition. They are studied in the vicinity of the lower critical point at temperatures above the critical temperature [1.05 < (η”η') < 2.0, corresponding to 0.05<A<0.4]. A is varied by changing the temperature of the mixture; (b) poly(ethylene glycol) (PEG)/dextran (D)/water mixtures at different compositions in the vicinity of the plait point at constant temperature [10<(η“/η')<40, corresponding to 0.762<A<0.950]. The liquid/liquid interfacial tension of both systems is small (σ<0.1 mN m−1). The experimental results are analysed in terms of theoretical work of Tryggvason and Aref (J. Fluid. Mech. 177, 207 (1985)). The viscous fingering process is treated as a two‐dimensional viscous flow. For small values of A (<0.12; system (C4El1/water) the growth rates of the viscous fingers in the upward and downward direction have about the same value and the fingers have a similar shape. At larger values of A (>0.3) the fingers formed by the phase with the higher viscosity advance faster into the phase with the lower viscosity than the fingers advancing in the opposite direction. This effect is pronounced in the system PEG/D/water for which A has large values (A>0.75). In this system the viscous fingers formed by the phase with the higher viscosity are long and narrow whereas that formed by the low viscosity phase are short and broad. The temperature dependence of the mean distance <l> between viscous fingers of the system C4E1/water advancing in opposite directions approaches the theoretically expected dependence at temperature differences (Tp‐Tc)>l K corresponding to a ratio (λmax/b) > 3 (λmax, wave length of fasted growing interfacial instability; b, width of the glass cell). The experiments show that the preferential wetting of the glass walls of the Hele‐Shaw cell by one of the coexisting liquid phases leads to a three‐dimensional shape of the viscous fingers.

AbstractMeasurements of the rate constant of the ortho‐para conversion of monomeric gaseous formaldehyde H2CO in mixtures with He, Ar, H2, N2, CO, O2, CH3F and SF6 are described. Separation of the nuclear spin isomers of formaldehyde was obtained by selective UV laser photolysis of ortho‐formaldehyde in the natural ortho‐para mixture. Inert gas pressure was varied up to atmospheric pressure, formaldehyde pressure was 2.8 mbar in all experiments. At low pressures a linear increase of the rate constant with the inert gas pressure was found in all gases. With the noble gases, this increase was very small. In mixture with H2, N2, O2 and SF6 the rate constant rises up to a maximum and then shows a steep decrease as a function of the inert gas pressure. With the noble gases, CO and CH3F only the increase of the rate constant with pressure could be measured. The results are compared to the theory of Curl et al. [37]for the pressure dependence of the nuclear spin state relaxation of formaldehyde.

AbstractBecause of contradictions in the literature, we reinvestigated the kinetics of the Birch reduction, i.e. the hydrogenation of benzene and its derivatives in metal ammonia solutions (MAS: containing solvated electrons e− and metal cations M+) with alcohols to yield the corresponding cyclohexa‐1,4‐dien compounds (e.g. 2 Li+2CH3OH+C6H6⟹2CH3OLi+C6H8). The kinetics of this reaction are obscured since the hydrogen reaction proceeds parallel to it (2Li+2CH3OH⟹2CH3OLi+H2). The two reactions differ in their activation energies (6.5 and 22.5 kJ/Mol resp.); and in the series of the alkali metals Li, Na and K the rate of the Birch reduction decreases, whereas that of the hydrogen reaction increases. However, in the metal concentration range around 0.01 M. both reactions have within the experimental error the same reaction order with respect to the metal (≈︁0.8). Both are accelerated by addition of alkali cations common to the dissolved alkali metal, and both are decelerated by addition of alkali cation complexing cryptands. Thus we conclude that the cations are involved in the kinetics of both reactions, probably by forming intermediate ion pairs or shifting pre‐equilibria in which solvated electrons are involved. The experimental data of both reactions can be described very well with the rate laws v(B) = kBf2[e−][Li+)[CH3OH][C6H6]and v(H)=kHf2[e−][Li+](CH3OH]resp. (f activity coefficients after Debye‐Hückel) inserting the concentrations of e− and Li+ as calculated from the known thermodynamics of LiAS. The experimental rate constants kB and kH are the products of the rate constants of the rate determining steps and the equilibrium constants of the pre‐equilibria.

AbstractThe high pressure phase behaviour of four liquid crystals, belonging to the class of laterally aryl‐substituted mesogens has been studied with differential thermal analysis. The pressure dependence of the phase transitions has been determined up to 300 MPa. Transition enthalpies have been determined with the aid of differential scanning calorimetry. Volume changes accompanying the phase transitions have been calculated using the Clausius‐Clapeyron equation. Several metastable phase transitions have been discovered.

AbstractWe have studied the adsorption of mercury on sapphire at temperatures and pressures close to the liquid‐vapour critical point (Tc= 1478°C, pc= 1673 bar, pc = 5.8 g/cm3) of mercury. The mercury film undergoes a first‐order phase transition known as prewetting. At low temperatures, the prewetting line meets the bulk coexistence curve tangentially at the wetting temperatures Tw = 1310°C. At high temperatures the prewetting line terminates at the prewetting critical point Tcpw = 1468°C and the prewetting pressure pcpw = 1586 bar lying close to the bulk critical point. In analogy with the line of compressibility maxima extending above the liquid‐vapor critical point, we can identify an extension of the prewetting phase line for T>Tcpw which marks the maximum in the two‐dimensional compressibility of the prewetting supercritical phase.

Berichte der Bunsengesellschaft für physikalische ChemieVolume 102, Issue 12 p. 1898-1898 Nachrichten/News Section Personalia/people First published: 22 June 2010 https://doi.org/10.1002/bbpc.19981021222AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume102, Issue12December 1998Pages 1898-1898 RelatedInformation