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Item Thermodynamic Functions for the System Ethanol-F Cyclohexane from Vapour Pressures and Enthalpies of Mixing(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (09), 1977) Stokes, Robin H.; Adamson, MarionActivity coefficients for the system ethanol + cyclohexane at 45°C are obtained from vapour pressure measurements using a stepwise dilution apparatus. Enthalpies of mixing for the range xA= 0.1 to 0.99 (xa= mole fraction of ethanol) supplementing those reported previously for the range up to xA= 0.16, are obtained at seven temperatures by isothermal dilution calorimetry. Conversion of the activity coefficients to 6.7°C shows that the activity data obtained previously from freezing-point measurements were in error, owing to suspected solid solution formation.Item Interpretation of the Thermodynamic, Spectroscopic and Dielectric Properties of Solutions of Ethanol in Cyclohexane in Terms of Association(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (07), 1977) Stokes, Robin H.A model is proposed to explain the thermodynamic, spectroscopic and dielectric properties of dilute solutions of ethanol in cyclohexane in terms of association into both open-chain and cyclic hydrogen bonded groups, with allowance for a Van der Waals interaction term. It proves necessary to specify: two standard enthalpies for formation of the H-bonds, h2=–21.2 kJ mol–1 for the dimer and h=–23.5 kJ mol–1 for all larger groups; three standard entropies of stepwise formation (for the dimer, trimer and all higher open-chain forms); and a standard entropy of formation from open-chain to cyclic groups, which are assumed to be present to a significant extent only for groups of more than four molecules. This model gives a quantitative reproduction of the activity coefficients, enthalpies of mixing and i.r. spectroscopic behaviour, and accounts for the initial decrease in the apparent dipole moment.Item Thermodynamic Study of Dilute Aqueous Solutions of Organic Compounds Part 5.—Open-chain Saturated Bifunctional Compounds(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Cabani, Sergio; Mollica, Vincenzo; Lepori, LucianoValues have been determined at 25°C of the changes in the free energy, enthalpy and entropy corresponding to the process of transfer from the ideal gas state to dilute aqueous solution for ethylene-diamine, 2-methoxyethylamine, 3-methoxypropylamine, 1,2-dimethoxymethane and four 2-alkoxy-ethanols (methoxy to n-butoxy). These data have been used to calculate the variations in the thermodynamic functions of hydration for the hypothetical process of introducing a Y group (Y = O, NH) into a monofunctional RX compound (X = O, NH, NH2, OH), either by breaking a C—C or a C—H bond. Evidence of strong interactions between hydrophilic centres in bifunctional compounds emerges. The strength and nature (entropic or enthalpic) of these interactions depend on both the type of functional groups and their relative distance.Item Kinetic and Thermodynamic Character of Reducing Species Produced on Pulse Radiolysis of Acetonitrile(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (2), 1977) Bell, Ian P.; Rodgers, Michael A. J.; Burrows, Hugh D.During nanosecond pulse radiolysis of liquid acetonitrile a transient optical absorption was observed in the spectral range 500 to 1500 nm. The extreme reactivity of this species towards solutes capable of accepting electrons allowed its assignment as a reducing entity. In the purest liquid prepared this species had a half-life of some 900 ns. Variable temperature studies showed that this reducing species, having an intense maximum near 1450 nm at + 62°C, was drastically reduced in absorption intensity at –40°C, where the decay character changed and a weak maximum was observed near 550 nm. It was concluded that the two species are different chemical forms of a reducing entity joined by an equilibrium. Tentative identification of the reversible change according to (CH3CN)–+ CH3CN ⇌(CH3CN)–2 with the monomeric anion as the infrared absorbing entity was based on thermodynamic considerations and the effects of adding polar liquids. Quantitative examination of the data allowed a value of –34.9 kJ mol–1 to be extracted for the binding energy of the anion dimer. Measurements of the yields of pyrene and trans-stilbene radical anion formed after pulse radiolysis of appropriate solutions led to the evaluation of G(reducing entity)= 1.03. In addition it was found that O– radicals, formed by reaction between (CH3CN)– and N2O, reacted with acetonitrile via both addition and abstraction routes. Further, in solutions containing tetracyanobenzene (TCNB) and O2, capture of the negative entity by O2 was followed by electron transfer from O–2 to TCNB.Item Thermodynamic Study of the Vaporization of Cerium Orthophosphate(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (1), 1977) Guido, M; Balducci, G; De Maria, G; Gigli, GThe high temperature Knudsen cell mass spectrometric technique has been used to study the vaporization behaviour of solid cerium orthophosphate over the temperature range 1700–1850 K. From the second- and third-law analyses of the equilibrium reaction: CePO4(s)= CeO2(g)+ PO2(g), the following standard heat of formation of CePO4(s) has been derived: ΔH°298,f[CePO4(s)]=–1898.5 ± 31.5 kJ mol–1. These results are discussed and compared with those obtained by other authors for other LnPO4 compounds.Item Generalised Forster Cycle: Thermodynamic and Extrathermodynamic Relationships Between Proton Transfer, Electron Transfer and Electronic Excitation(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (1), 1977) Grabowski, Zbigniew R.; Rubaszewska, WieseawaThe thermodynamic quantities characterizing one electron reduction, protonation and electronic excitation, are mutually related in the ground and excited states by 6 thermodynamic (or approximate thermodynamic) cycles. The system of cycles is used to predict unknown values, and its validity may be extended to other compounds by means of extra thermodynamic (e.g., Hammett-type) relations. Examples of known data concerning pK and pK* values of protolytic equilibria for the oxidized (Ox) and reduced (R) species are evaluated, tabulated and discussed in a search for a correlation between the changes of pK on excitation (ΔpK*) and on reduction (ΔpKe). Both values are thermodynamically independent but a general common trend is empirically observed in several groups of systems. Some rules are derived for the excited state redox potentials and their dependence on pH, which may be useful for photochemistry.Item Thermodynamic Study of the 1 : 1 Solid Compound, Hexafluorobenzene-Benzene(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (11), 1974) Brennan, J. S.; Brown, N. M. D. Brown; Swinton, Findlay L.A study of the 1 : 1 solid compound hexafluorobenzene–benzene using a differential scanning calorimeter has enabled an estimate to be made of the enthalpy of formation of the compound when it is formed from the two pure solids. The measured value, + 1.0 ± 0.3 kJ mol–1, is small and positive and is good evidence that the compound is stabilized by preferred geometrical packing effects probably enhanced by weak electrostatic forces rather than by any of the normal specific intermolecular interactions of the charge transfer type. A solid–solid transition was detected at 249.2 K. This is thought to be a genuine order–disorder transition brought about by a partial disordering of the regular alternate packing sequence observed at lower temperatures.Item Thermodynamic Properties of Fluorine Compounds: Part 12.Low-temperature Heat Capacity and Entropy of 1,3,5-Trichloro-2,4,6-trifluorobenzene(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (5), 1973) Andon, Richard J. L.; Martin, John F.The heat capacity of 1,3,5-trichloro-2,4,6-trifluorobenzene was measured by adiabatic calorimetry from 14 to 347 K, and thermodynamic functions were calculated from the results. The heat capacity curve exhibited an anomalous region between 285 and 305 K. The triple point temperature was measured as 335.01 K and the entropy of the crystals at 298.15 K was found to be 243.3 J K–1 mol–1.Item Thermodynamic Properties of Aliphatic Halogen Compounds: Part 1.—Vapour Pressure and Critical Properties of 1,1,1-Trichloroethane(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (5), 1973) Ambrose, D.; Sprake, C. H. S.; Townsend, R.The vapour pressure of 1,1,1-trichloroethane was measured in the range 15 to 200 kPa by comparative ebulliometry, and the critical temperature and pressure were also measured. The observed values of the vapour pressure were fitted by equations, and one of them, a fourth order Chebyshev polynomial, is recommended for use if interpolation between 200 kPa and the critical pressure is required.Item Mass Spectrometric Determination of the Thermodynamic Properties of the Vapour Species from Alumina(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (2), 1972) Farber, Milton; Srivastava, R. D.; Uy, O. M.The vapour species over Al2O3(c) were determined mass spectrometrically from an alumina effusion cell. These data are in good agreement with previously published weight loss data since the partial pressures of the suboxides, AlO, Al2O, AlO2 and Al2O2 were found to be of the same order as those of the elements, Al and O. New values were determined for the ΔHf298K of AlO, Al2O, AlO2 and Al2O2 of 17.0 ± 2.0, –33.2 ± 3.0, –44.3 ± 2.0 and –113.6 ± 2.0 kcal/mol, respectively. Excellent agreement was obtained between second and third law studies.