The excess thermodynamic functions of three-component Lennard-Jones systems based on binary distribution functions

Integral equation theory was used to study the binary distribution functions of the excess properties of three-component Lennard-Jones mixtures. The results obtained for the behavior of the excess functions of caloric properties (internal energy, enthalpy, and isochoric heat capacity) are reported. The influence of the third component with various potential parameters on excess functions was studied. Calculations were performed for systems under super-and subcritical conditions with different sizes of molecules, σ₁/σ₂ = 1–4, and attraction energies between them, ?₁/?₂ = 1–4. The results were compared with numerical experiment data to find that the approach used was fairly accurate     

Molecular relaxation processes in triatomic molecules. II. The N2–CO2 system

Translation–vibration (T–V) and vibration–vibration (V–V) energy transfer processes in the N₂–CO₂ system were investigated using classical trajectory techniques. Two empirical interaction potentials were employed. One is comprised of independent, atom–atom Morse-type functions operating between nonbonded atoms. The other included these atom–atom Morse functions plus Coulombic terms to account for the quadrupole–quadrupole intertion. Both interaction potentials led to similar T–V results. However, the result that CO₂(v₃) is excited ～10³ times more efficiently than N₂(v = 1) was obtained, which is at variance with existing analytical theories of T–V energy transfer employing purely repulsive short-range potentials. Different V–V energy transfer probabilities were obtained from the two interaction potentials. The most important finding is that only when electrostatic orientation effects are combined with short-range repulsive interactions is the near-resonant V–V transfer found to be the dominant energy transfer path. This interaction potential also crudely accounts for the negative temperature dependence observed for this near-resonant V–V transfer at low temperatures (300–1000°K).     

Polymerization of acrylamide with persulfate–thiomalic acid initiator

The redox system of potassium persulfate–thiomalic acid (I₁–I₂) was used to initiate the polymerization of acrylamide (M) in aqueous medium. For 20–30% conversion the rate equation is where R_p is the rate of polymerization. Activation energy is 8.34 kcal deg^?1 mole^?1 in the investigated range of temperature 25–45°C. M_n is directly proportional to [M] and inversely to [I₁]. The range of concentrations for which these observations hold at 35°C and pH 4.2 are [I₁] = (1.0–3.0) × 10^?3, [I₂] = (3.0–7.5) × 10^?3, and [M] = 5.0 × 10^?2–3.0 × 10^?1 mole/liter.     

Fully converged sudden rotation total integral cross sections for 4He + H2 (ν = 0, j = 0) → 4He + H2 (ν′ = 1, j′)

Total integral cross sections for ⁴He + H₂ (ν = 0, j = 0) → ⁴He + H₂ (ν′ = 1, j′ = 0, 2) have been calculated in the total energy range 1.2 to 5.5 eV, according to a quantal sudden approximation for the H₂ rotational degrees of freedom and a close coupling expansion of the vibrational degree of freedom. Convergence of the above cross sections is investigated by employing four vibration basis sets in the close coupling calculations, i.e., ν = 0,1, ν = 0,1, 2, ν = 0, 1, 2, 3 and ν = 0, 1, 2, 3, 4. Between 4.2 and 5.5 eV calculations were done with three vibration basis sets; ν = 0.–4, ν = 0–5, and ν = 0–6. It is found that at least four vibrational basis functions are needed to converge (to within 5–10%) these cross sections in the above energy range. Comparison of breathing sphere calculations and summed sudden rotation results shows good agreement for the (weakly anisotropic) Mies-Krauss potential. However, as expected the former results underestimate the vibrational 0 → 1 total integral cross sections.     

The reaction of O(1D) with CH4

The room-temperature photolysis of N₂O (10–100 torr) at 2139 Å to produce O(¹D) has been studied in the presence of CH₄ (10–891 torr). The reactions of O(¹D) with CH₄ were found to be The method of chemical difference was used to measure the rate constant ratio k₄/(k₂ + k₃), where reactions (2) and (3) are The CH₃ radicals produced in reaction (4) react with the O₂ and NO produced in reactions (2) and (3). Thus, near the endpoint of the internal titration, ?{C₂H₆} gives an accurate measure of k₄/(k₂ + k₃). For the translationally energetic O(¹D) atoms produced in the photolysis, k₄/(k₂ + k₃) = 2.28 ± 0.20. However, if He is added to remove the excess translational energy, then k₄/(k₂ + k₃) drops to 1.35 ± 0.3.     

Thermal analysis kinetics of thermal decomposition of nickel–viscose composite fiber

In this study, the thermal decompositions of nickel composite fibers (NCF) under different atmospheres of flowing nitrogen and air were investigated by XRD, SEM–EDS, and TG–DTG techniques. Non-isothermal studies indicated that only one mass loss stage occurred over the temperature regions of 298–1,073 K in nitrogen. The mass loss was from the decomposition. But after this decomposition, nickel was oxidized in air, when the temperature was high enough. In nitrogen media, the model-free kinetic analysis method was applied to calculate the apparent activation energy (E _a) and pre-exponential factor (A). The method combining Satava–?esták equation with one TG curve was used to select the suitable mechanism functions from 30 typical kinetic models. Furthermore, the Coats–Redfern method was used to study the NCF decomposition kinetics. The study results showed that the decomposition of NCF in nitrogen media was controlled by three-dimension diffusion; mechanism function was the anti-Jander equation, the apparent activation energy (E _a) and the pre-exponential factor (A) were 172.3 kJ mol^?1 and 2.16 × 10⁹ s^?1, respectively. The kinetic equation could be expressed as following: $$ \frac{{{\text{d}}\alpha }}{{{\text{d}}T}} = \frac{{ 2. 1 6\times 1 0^{ 9} }}{\beta }{ \exp }\left( {\frac{ - 2 0 7 2 4. 1}{T}} \right)\left\{ {\frac{ 3}{ 2}(1 + \alpha )^{2/3} [(1 + \alpha )^{1/3} - 1]^{ - 1} } \right\}. $$      

New approach to simplify the equation for the excess Gibbs free energy of aqueous solutions of electrolytes applied to the modelling of the NH3–CO2–H2O vapour–liquid equilibria

A new, simple, empirical equation for G^E (excess Gibbs free energy) of electrolyte solutions is proposed in which, contrary to the commonly used Pitzer equation, binary and ternary interaction parameters relate to the interactions of electrolytes in a solution rather than to the interactions of real species in a solution (i.e., anions, cations and nondissociated molecules). Such an approach radically reduces the number of parameters in the new equation for G^E as compared with the Pitzer equation and consequently significantly simplifies their calculation. The efficiency of the new approach is demonstrated on the example of modelling the vapour–liquid equilibria of the industrially important and widely investigated NH₃–CO₂–H₂O system.     

Kinetics and mechanism of the reaction between hypochlorous acid and tetrathionate ion

The reaction has been studied spectrophotometrically monitoring the absorbance in the 240–400 nm wavelength range. The spectra of the reactants, intermediates, and products in this system are overlapping; thus special programs [ 1 , 2 ] have been used (and tested) to unravel the kinetics and mechanism of the reaction. The stoichiometry of the reaction in excess hypochlorous acid is S₄O₆²⁻ + 7HOCl + 3H₂O → 4SO₄²⁻ + 7Cl⁻ + 13H⁺. Various experiments are presented to show that—in excess tetrathionate—the reaction produces a light‐absorbing intermediate identified as S₂O₃Cl⁻. The intermediate slowly hydrolyzes into sulfur and sulfate and it yields pentathionate in excess tetrathionate. The rate‐determining steps and their rate constants are The further oxidation of S₂O₄²⁻ and SO₃²⁻ by HOCl to sulfate are fast processes. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 395–402, 2000     

Salt effect on the enthalpy of mixing of water+methanol at 303.15 K

The excess enthalpy of the miscible water–methanol system has been measured at 303.15 K in an isothermal batch calorimeter with vapour space. The effect of the salts NH₄Cl, CdCl₂ and HgCl₂ on H^E was studied. A decreasing trend in excess enthalpy for NH₄Cl and HgCl₂ but an increasing trend for CdCl₂ with increasing salt concentrations have been observed. The experimental values of H^E have been correlated using a modified Redlich–Kister equation and the binary parameters have been estimated. The deviations were calculated and reported.     

Shock-initiated decomposition of tetramethylgermane and the reaction of methyl radicals with toluene

The shock-initiated decomposition of tetramethylgermane (1078–1242 K) has been found to involve successive elimination of methyl radicals with the rate constant k₁ for the first step given by In the presence of excess toluene the products were CH₄ (major), C₂H₄, and C₂H₆. Results relevant to the reaction of methyl radicals with toluene compared to methyl radical recombination are discussed.     

Thermodynamics of liquid propane + cyclopropane

The vapour pressure differences between a mixture of (propane + cyclopropane) and cyclopropane and between propane and cyclopropane have been measured simultaneously with the absolute vapour pressure of cyclopropane. This was done at 13 temperatures between 175 K and 210 K, as a function of composition. The mixtures show small positive deviations from Raoult's law. The excess molar Gibbs energy (G_m^E) has been calculated from the vapour pressure data fitted to the equation G_m^E/(RTx₁x₂ = (−0.2490±0.0072)+(81.8±1.4)/T. The estimated value of the excess molar enthalpy (H_m^E) for the equimolar composition, in the same temperature range is 170 ± 4 J mol⁻¹. The results were interpreted using Deiters' equation of state.     

A kinetic study of the thermal elimination of hydrogen fluoride from 1,2-difluoroethane. Determination of the bond dissociation energies D(CH2F?CH2F) and D(CH2F?H).

The kinetics of the thermal elimination of HF from 1,2-difluoroethane have been studied in a static system over the temperature range 734–820°K. The reaction was shown to be first order and homogeneous, with a rate constant of where θ = 2.303RT in kcal/mole. The A-factor falls within the normal range for such reactions and is in line with transition state theory; the activation energy is similarly consistent with an estimate based on data for the analogous reactions of ethyl fluoride and other alkyl halides. The above activation energy has been compared with values of the critical energy calculated from data on the decomposition of chemically activated 1,2-difluoroethane by the RRKM theory and the bond dissociation energy, D(CH₂F? CH₂F) = 88 ± 2 kcal/mole, derived. It follows from thermochemistry that ΔH_f⁰(CH₂F) = -7.8 and D(CH₂F? H) = 101 ± 2 kcal/mole. Bond dissociation energies in fluoromethanes and fluoroethanes are discussed.     

The kinetics of radiation-induced hydrogen abstraction by CCl3 radicals in the liquid phase: Cyclohexene

The kinetics of hydrogen abstraction from cyclohexene by CCl₃ radicals were studied in CCl₄ solution as a function of cyclohexene concentration and temperature in the range of 26–140°C. The CCl₃ radicals were produced both by radiolysis of CCl₄ and by photolysis of CCl₃Br. The rate constant for the reaction was found to be given by the equation where θ = 2.303 RT kcal/mol. This activation energy leads to C? H bond strength for the allylic hydrogen of 85 ± 1 kcal/mol, which means a resonance stabilization energy of 11 ± 1.5 kcal/mol for the C-C₆H₁₁ radical.     

Two Alkali‐Metal Yttrium Tellurides: Single Crystals of Trigonal KYTe2 and Hexagonal RbYTe2

While attempting to synthesize the potassium and rubidium copper diyttrium tetratellurides KCuY₂Te₄ and RbCuY₂Te₄ in analogy to CsCuY₂Te₄ from 1:1:4‐molar mixtures of the elements (copper, yttrium and tellurium) with an excess of KBr or RbBr as flux and potassium or rubidium source, brown plate‐shaped crystals of KYTe₂ and RbYTe₂ with triangular cross‐section were obtained instead after 14 days at 900 °C in torch‐sealed evacuated silica tubes. These new ternary yttrium tellurides crystallize in the trigonal (KYTe₂) or hexagonal system (RbYTe₂) with space group R m (no. 166) or P6₃/mmc (no. 194), respectively. With unit cell dimensions of a = 439.51(2) pm, c = 2255.48(9) pm (c/a = 5.132) for KYTe₂ and a = 443.26(2) pm, c = 1729.15(7) pm (c/a = 3.901) for RbYTe₂, both crystal structures exhibit cadmium‐halide analogous layers spreading out parallel to the (001) planes, which are formed by edge‐condensation of the involved [YTe₆]^9– octahedra (d(Y³⁺–Te^2–) = 308–309 pm). Charge compensation and three‐dimensional linkage of these anionic layers are achieved by monovalent interlayer alkali‐metal cations residing in trigonal antiprismatic (K⁺ in α‐NaFeO₂‐type KYTe₂, d(K⁺–Te^2–) = 324 pm, 6×) or prismatic coordination (Rb⁺ in β‐RbScO₂‐type RbYTe₂, d(Rb⁺–Te^2–) = 365 pm, 6×) of six Te^2– ions each.     

Kristallstrukturen der iso‐Thiocyanatoberyllate (Ph4P)2[Be(NCS)4] und (Ph4P)4[{Be2(NCS)4(μ‐NCS)2}{Be2(NCS)6(μ‐H2N2C2S2)}]

Bis(tetraphenylphosphonium) hexachloridodiberyllate, (Ph₄P)₂[Be₂Cl₆], reacts with excess trimethylsilyl‐iso‐thiocyanate to give a mixture of colourless single crystals of (Ph₄P)₂[Be(NCS)₄] ( 1 ) and (Ph₄P)₄[{Be₂(NCS)₄(μ‐NCS)₂}{Be₂(NCS)₆(μ‐H₂N₂C₂S₂)}] ( 2 ), which can be separated by selection. Both complexes were characterized by X‐ray diffraction. Compound 1 can be prepared without by‐products by treatment of (Ph₄P)₂[BeCl₄] with excess Me₃SiNCS in dichloromethane solution. 1 : Space group I4₁/a, Z = 4, lattice dimensions at 100(2) K: a = b = 1091.2(1), c = 3937.1(3) pm, R₁ = 0.0474. The [Be(NCS)₄]^2– ion of 1 forms tetragonally distorted tetrahedral anions with Be–N distances of 168.4(2) pm and weak intermolecular S ··· S contacts along [100] and [010]. 2 ·4CH₂Cl₂: Space group P , Z = 1, lattice dimensions at 100(2) K: a = 919.5(1), b = 1248.3(1), c = 2707.0(2) pm, α = 101.61(1) °, β = 95.08(1) °, γ = 94.52(1) °, R₁ = 0.103. Compound 2 contains two different anionic complexes in the ratio 1:1. In {Be₂(NCS)₄(μ‐NCS)₂}^2–, the beryllium atoms are connected by (NCS)^– bridging groups forming centrosymmetric eight‐membered Be₂(NCS)₂ rings with distances Be–N of 168(1) pm and Be–S of 235.2(9) pm. The second anion {Be₂(NCS)₆(μ‐H₂N₂C₂S₂)}^2– consists of two {Be(NCS)₃}^– units, which are linked by the nitrogen atoms of the unique dimeric cyclo‐addition product of HNCS with Be–N distances of 179(1) pm.     

Thermodynamic properties of DCl in D2O solution from 5 to 50°C

The themodynamic properties of solutions of deuterium chloride (DCl) in deuterium oxide (D₂O) have been determined from emf measurements of the electrochemical cell without transference from 5 to 50°C, and from 0.002 to 1.0 mol-kg^–1. The standard potential of the silver/silver chloride electrode relative to the platinum/deuterium electrode has been determined. An equation for the Gibbs energy as a function of temperature has been derived from which the enthalpy, entropy, and heat capacity have been computed. Equations for the activity coefficient and the osmotic coefficient of DCl in D₂O have been developed. The excess Gibbs energy of the solution and the excess partial molar free energy as a function of temperature have been calculated, from which the other excess thermodynamic properties have been computed. The values for the heat capacity and the apparent molar heat capacity have been compared with calorimetric data in the literature. The relative partial molar enthalpy has been calculated. The solvent isotope effect on the excess thermodynamic functions is discussed.     

Die Kristallstruktur des Diacetonalkohol‐Komplexes [Mn(DAA)3]2+[MnI4]2– · DAA

Crystal Structure of the Diacetone Alcohol Complex [Mn(DAA)₃]²⁺[MnI₄]^2– · DAA The title compound has been prepared from MnI₂ and excess diacetone alcohol (4‐hydroxy‐4‐methyl‐2‐pentanon) to give brown single crystals which were suitable for a crystal structure determination. Space group P2₁/c, Z = 4, lattice dimensions at 157 K: a = 1158.3(1), b = 1806.0(1), c = 1846.5(2) pm, β = 97.421(8)°, R₁ = 0.0381. The structure consists of [Mn(DAA)₃]²⁺ ions with distorted octahedral environment of the manganese atom, tetrahedral [MnI₄]^2– ions and a diacetone alcohol molecule which is connected by two hydrogen bridges with the complex cation.     

Kinetics of the gas-phase reaction between iodine and monogermane and the bond dissociation energy D(H3Ge?H)

The title reaction has been investigated in the temperature range of 403–446 K. Monoiodogermane and di-iodogermane together with hydrogen iodide were the main products, although at high conversions at least one other product was formed. GeH₃I is clearly the primary product. Initial rates were found to obey the rate law over a wide range of initial iodine and monogermane pressures. Secondary reactions (of GeH₃I with I₂) affect the subsequent kinetics, although at sufficiently high initial reactant ratios ([GeH₄]₀/[I₂]₀ ≥ 100) an integrated rate equation fits the data with the same rate constants as the initial rate expression. The observed kinetics are consistent with an iodine atom abstraction chain mechanism, and for the step log k₁ (dm³/mol·s) = (11.03 ± 0.13) – (52.3 ± 1.0 kJ/mol)/RT ln 10 has been deduced. From this the bond dissociation energy D(GeH₃? H) = 346 ± 10 kJ/mol (82.5 kcal/mol) is obtained. The significance of this value, together with derived values for Ge–Ge and Ge–C bond strengths, is discussed.