Dichlorosilylene: Rate constant for the gas-phase reaction with nitric oxide

Using the recently detected intense UV absorption spectrum of it has been established that SiCl₂ reacts with nitric oxide in the gas phase with a bimolecular rate constant, k(SiCl₂+NO), of (1.6±0.1)×10⁹ M⁻¹s⁻¹ at 25°C.     

On the influence of ionic strength on the equilibrium constant of an ion-molecule reaction

Concentration formation constants for the 18-crown-6-sodium ion complex in anhydrous methanol solutions were measured as a function of the ionic strength of the solution. The K_c values remained reasonably constant for I_c ? 0.05 mol dm^?3 At higher ionic strengths the K_c values begin to decrease. The infinite-dilution formation constant was 2.2 × 10⁴.     

花团状纳米铜的制备和催化性能

采用液相化学还原法,以六元瓜环(Q[6])为修饰剂,CuSO4·5H2O为铜源,抗坏血酸为还原剂制备纳米铜.采用X射线粉末衍射、扫描电镜及紫外-可见吸收光谱对产物进行结构和形貌表征.结果表明,产物纳米铜呈特殊的花团状结构,花团直径约为2.0μm.花团状纳米铜对染料罗丹明B和次甲基蓝的催化结果显示,在40℃和H2O2辅助下,60mg/L花团状纳米铜在120min内对罗丹明B和次甲基蓝的降解率大于83%.     

Rate coefficients and equilibrium constant for the CH2CHO + O2 reaction system

The kinetics of the CH2CHO + O2 reaction was experimentally studied in two quasi-static reactors and a discharge flow-reactor at temperatures ranging from 298 to 660 K and pressures between 1 mbar and 46 bar with helium as the bath gas. The CH2CHO radicals were produced by the laser-flash photolysis of ethyl vinyl ether at 193 nm and by the reaction F + CH3CHO, respectively. Laser-induced fluorescence excited at 337 or 347.4 nm was used to monitor the CH2CHO concentration. The reaction proceeded via reversible complex formation with subsequent isomerization and fast decomposition: CH2CHO + O2 <= => O2CH2CHO --> HO2CH2CO --> products. The rate coefficients for the first and second steps were determined (k1, k-1, k2) and analyzed by a master equation with specific rate coefficients from the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Molecular and transition-state parameters were obtained from quantum chemical calculations. A third-law analysis led to the following thermodynamic parameters for the first step: Delta(R)S degrees 300K(1) = -144 J K(-1) mol(-1) (1 bar) and Delta(R)H degrees 300K(1) = (-101 +/- 4) kJ mol(-1). From the falloff analysis, the following temperature dependencies for the low- and high-pressure limiting rate coefficients were obtained: k1(0) = 5.14 x 10(-14) exp(210 K/T) cm(-3) s(-1); k1(infinity) = 1.7 x 10(-12) exp(-520 K/T) cm(-3) s(-1); and k2(infinity) = 1.3 x 10(12) exp[-(82 +/- 4) kJ mol(-1)/RT] s(-1). Readily applicable analytical representations for the pressure and temperature dependence of k1 were derived to be used in kinetic modeling.     

Chemical equilibrium model for the thermodynamic properties of mixed aqueous micellar systems: Application to thermodynamic functions of transfer

Mixed micelles can be formed in water between various pairs of hydrophobic solutes such as surfactants, alcohols and hydrocarbons. These systems can often be studied through the thermodynamic functions of transfer of one of the solutes, usually kept near infinite dilution, from water to an aqueous solution of the other solute. When mixed micelles are formed, these functions change significantly, and often go through extrema, in the region where the binary system micellizes or undergoes some microphase transition.Three main effects are responsible for the observed trends: pair-wise interactions between both solutes in the monomeric form, a distribution of the reference solute between the aqueous and micellar phases and a shift in the monomer-micelle equilibrium in the vicinity of the reference solute. Simple equations can be derived for these three effects which can account for the sign and magnitude of the observed trends using parameters which are derived for the most part from the two binary systems.     

Dichlorosilylene: Rate constant for reaction with carbon monoxide and nitrous oxide

The absolute rate constanss for the gas-phase reactions of 1,1-dichlorosilylene with carbon monoxide and nitrous oxide have been determined using the flash photolysts-kinetic absorpiton spectroscopy technique. The bimolecular rate constant values at 25° C are: $$\begin{gathered} k\left( {Cl_2 Si + CO} \right) = \left( {6.3 \pm 0.7} \right) \times 10^8 M^{ - 1} s^{ - 1} \hfill \\ k\left( {Cl_2 Si + N_2 O} \right) = \left( {5.7 \pm 0.3} \right) \times 10^8 M^{ - 1} s^{ - 1} \hfill \\ \end{gathered} $$      

Interchain electron donor–acceptor complexes. Determination of equilibrium constant and thermodynamic parameters in the solid state

The interpolymeric electron donor–acceptor (EDA) complex of donor poly[(N-ethylcarbazol-3-yl)methyl methacrylate] (PHMCM-2) with acceptor poly-(2-[(3,5-dinitrobenzoyl)oxy]ethyl methacrylate) (PDNBM-2) presents a single glass transition temperature and a decomplexation endotherm on differential scanning calorimetric (DSC) thermograms. This system is considered a “polymer blend model” which exhibits a lower critical solution temperature (LCST). Phase separation of this blend is kinetically controlled and positive deviations of the glass transition temperatures from weight average values suggest that it behaves as a thermally reversible crosslinked network. Calorimetric methods to determine the heats of mixing of small molecule complexes in solution were adapted for this solid state blend to estimate the equilibrium constant (K_eq) and other thermodynamic parameters. Applying a computer iterative procedure and assuming 1 : 1 stoichiometry, a least-squares fit was found for several different donor molecular weights with three different high molecular weight acceptors. At moderate molecular weights, K_eq rises to represent saturation fractions near unity as found in biological systems. K_eq decreases for higher molecular weights, possibly due to trapped chain entanglements. These results are supported by a composition-independent, “horizontal line” phase diagram, thus resembling the completely complexed/denaturation process in DNA.     

On the coordination reaction of pyridine by chloroindiumtetraphenylporphyrin and its thermodynamic properties

The axial interaction of chloroindiumtetraphenylporphyrin with pyridine is studied in a mixed binary benzene-pyridine solvent of variable composition. Thermodynamic parameters of the process are determined. It is concluded on the basis of the results that the binding of pyridine to chloroindiumtetraphenylporphyrin is a low-characteristic reaction.     

Effects of ion solvation and volume change of reaction on the equilibrium and morphology in cation-exchange reaction of nanocrystals

The effects of cation solvation and the volume change (Delta V) of reaction on the equilibrium and the morphology change in the cation-exchange reactions of metal chalcogenide nanocrystals, CdE --> M(x)E(y) (E = S, Se, Te; M = Pd, Pt), were investigated. Since the solvation of cations is an important controllable factor determining the free energy of the reaction, the effect of varying cation solvation conditions on the equilibrium of the reaction was examined. A two-phase solvent environment, where the cations involved in the exchange reaction were preferentially solvated in different phases by using selective cation complexing molecules, was particularly efficient in increasing the thermodynamic driving force. The effect of Delta V of reaction on the morphology of the product nanocrystals was also investigated. Depending on the stress developed in the lattice during the reaction, product nanocrystals underwent varying degrees of morphological changes such as void formation and fragmentation in addition to the preservation of the original morphology of the reactant nanocrystals. The knowledge of the effect of ion solvation and Delta V of reaction on the equilibrium and product morphology provides a new strategy and useful guides to the application of cation-exchange reactions for the synthesis of a broader range of inorganic nanocrystals.     

Effects of protonation on the thermodynamic properties of alkyl dimethylamine oxides

The effects of protonation on alkyldimethyl amine oxide micelles are reviewed, mainly with regard to dodecyl and tetradecyl homologs. The topics discussed are hydrogen ion titration properties, critical micelle concentration (CMC), area per surfactant and micelle aggregation number. A hydrogen bond hypothesis is proposed to interpret the several characteristic results associated with protonation: between two cationic species as well as between the non-ionic-cationic pair. The dipole-dipole interaction of the non-ionic micelle is discussed in relation to both: (a) the unusually high CMC values of the non-ionic micelles compared with other non-ionic surfactants with the same hydrocarbon chain; and (b) the reversal of the stability of the non-ionic and the cationic micelles at high ionic strengths. Two different approaches of the salting out effect on the ionic micelles are compared, the Chan-Mukerjee approach and ours, in relation to the non-linear Corrin-Harkins relation. The obtained salting out constants of the surfactants carrying a dodecyl chain decreased as the head group becomes more polar. Infrared and 13C-NMR spectra data are examined from the point of the specific interaction claimed by the hydrogen bond model. Mixed surfactant systems including amine oxides and the solid state phase behavior of amine oxides are both briefly reviewed.     

A study of the thermodynamic properties and dehydration reaction kinetics of some salt-hydrates

Correlations were determined between heat capacity and temperature and phase change enthalpy of Ba(OH)₂·8H₂O. The phase diagram and DSC curve of the binary system Na₂CO₃·10H₂O?Na₂HPO₄·12H₂O were determined The kinetics of the dehydrating reaction of Ba(OH)₂·8H₂O, Na₂CO₃·10H₂O and Na₂HPO₄·12H₂O were measured and theoretically analyzed by TG.     

Excess thermodynamic properties and vapor-liquid equilibrium data for then-butylamine+p-dioxane system at 25°C

Excess values of molar volumes, viscosities, molar enthalpies, Gibbs molar energies, surface tensions and molar diamagnetic susceptibilities were calculated at 25°C for then-butylamine+p-dioxane system. The observed deviations from the ideality were explained on the basis of intermolecular interactions. Van Laar's equations were the best in predicting activity coefficients for this system.     

Overall rate constant measurements of the reaction of chloroalkylperoxy radicals with nitric oxide

The overall rate constants of the NO reaction with chloroalkylperoxy radicals derived from the Cl-initiated oxidation of several atmospherically abundant alkenes-ethene, propene, 1-butene, 2-butene, 2-methylpropene, 1,3-butadiene, and isoprene (2-methyl-1,3-butadiene)-were determined for the first time via the turbulent flow technique and pseudo-first-order kinetics conditions with high-pressure chemical ionization mass spectrometry for the direct detection of chloroalkylperoxy radical reactants. The individual 100 Torr, 298 K rate constants for each monoalkene system were found to be identical within the 95% confidence interval associated with each separate measurement, whereas the corresponding rate constants for 1,3-butadiene and isoprene were both approximately 20% higher than the monoalkene mean value. Our previous study of the reaction of hydroxylalkylperoxy radicals (derived from the OH-initiated oxidation of alkenes) with NO yielded identical rate constants for all of the alkenes under study, with a rate constant value within the statistical uncertainty of the value determined here for the NO reaction of chloroalkylperoxy radicals derived from monoalkenes. Thus, the reaction of NO with chloroalkylperoxy radicals derived from dialkenes is found to be significantly faster than the NO reaction with either chloroalkylperoxy radicals derived from monoalkenes or hydroxyalkylperoxy radicals derived from either mono- or dialkenes.     

Axial-base equilibrium and thermodynamic studies of ribosylcobalamins

Thermodynamic and equilibria properties of two vitamin B12 coenzyme analogues, i.e. 1-methyl-5-deoxy--d-(–)ribofuranosylcobalamin (RibCbl) and 1-methyl-5-deoxy-2,3-isopropylidene--d-(–)ribofuranosylcobal- amin (Rib*Cbl) were studied by u.v.-vis. spectroscopy. Their temperature-dependent equilibria between 6-coordinate base-on species and 5-coordinate unprotonated base-off species, and pH-dependent equilibria for the protonation and displacement of 5,6-dimethylbenzimidazole at 25°C have been examined. Values of H and S in neutral solution and at pH 4.00, and the axial base pKa were determined. Comparing the results with those for coenzyme B12 and other cobalamins, it has been found that H and S values for two ribosylcobalamins fall in the range of organocobalamins, but for RibCbl*, a ca. 1 unit difference in pKa values exists. The effect of the ribofuranose structure on the Co-N(dbzm) strength is considered.     

Oxygen equilibrium pressure above V2O5−x and thermodynamic properties of this oxide system

Measurements of oxygen equilibrium pressure above the V₂O_5?x oxide system have been performed within the temperature range 575 to 615°C. The results have been used to determine the standard enthalpy and entropy in the reaction V₆O₁₃ + O₂ = 3 V₂O₅. The thermodynamic properties of the V₂O_5?x system (at x < 1) cited in the literature have been discussed for all the equilibria postulated.     

Conditions for attainment of thermodynamic equilibrium for the Ag/Hg system

Following a previous study on the influence of the size of silver particles used in dental alloys on the conditions for the attainment of thermodynamic equilibrium, results are presented on the influence of the particle shape factor. Calorimetric results obtained using different particle forms are compared with those derived from a mathematical model in which it is considered that silver particles can assume a spherical or cylindrical (flat or narrow) shape. It appears that the thermal effects obtained by computation are closer to those obtained by calorimetric experimentation when the sphere of the model is transformed into either a disc or a rod.     

A new method for the determination of thermodynamic equilibrium constants in separation processes

A new approach to the determination of thermodynamic equilibrium constants in ion-exchange and solvent extraction processes is described. A plot of the logarithm of the distributing species activity in the aqueous phase as a function of its concentration in the non-aqueous phase has an inflection point. The ordinate of the inflection point gives directly the logarithm of the thermodynamic equilibrium constant of the reaction considered. This was made possible by finding that the ratio between n power of the free extractant molecule (or free site) activity and the activity of the distributing species-extractant complex is unity as this point.     

Adsorption and thermodynamic properties of active sites of a pyrogenic aluminium oxide surface

Differential isosteric adsorption heats and entropies of adsorption of both n-pentane and diethyl ether on hydrated and dehydrated surfaces of pyrogenic alumina (S=140 m²/g) in the coverage range of 0.15–1.0 have been calculated from the adsorption isotherms.     

Crystal structure and thermodynamic properties of dipotassium diiron(III) hexatitanium oxide

In the present work, the temperature dependence of heat capacity of dipotassium diiron(III) hexatitanium oxide has been measured for the first time in the range from 10 to 300 K by means of precision adiabatic vacuum calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity $ C_{p}^{ \circ } (T) $ , enthalpy $ H^{ \circ } (T) - H^{ \circ } (0) $ , entropy $ S^{ \circ } (T) - S^{ \circ } (0), $ and Gibbs function $ G^{ \circ } (T) - H^{ \circ } (0) $ for the range from T → 0 to 300 K. The structure of K₂Fe₂Ti₆O₁₆ is refined by the Rietveld method: space group I4/m, Z = 1, a = 10.1344(2) Å, c = 2.97567(4) Å, V = 305.618(7) Å³. The high-temperature X-ray diffraction was used for the determination of coefficients of thermal expansion.     

Study on the thermodynamic properties of cholesterol

The standard molar enthalpy of combustion of cholesterol was measured at constant volume. According to value of Δ_r U _m^θ(−14358.4±20.65 kJ mol⁻¹), Δ_r H _m^θ(−14385.7 kJ mol⁻¹) of combustion reaction and Δ_f H _m^θ(2812.9 kJ mol⁻¹) of cholesterol were obtained from the reaction equation. The enthalpy of combustion reaction of cholesterol was also estimated by the average bond enthalpies. By design of a thermo-chemical recycle, the enthalpy of combustion of cholesterol were calculated between 283.15∼373.15 K. Besides, molar enthalpy and entropy of fusion of cholesterol was obtained by DSC technique.