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21.
In this critical review, the significance of the term 'activity' is examined in the context of the properties of aqueous solutions. The dependence of the activity of water(l) at ambient pressure and 298.15 K on solute molality is examined for aqueous solutions containing neutral solutes, mixtures of neutral solutes and salts. Addition of a solute to water(l) always lowers its thermodynamic activity. For some solutes the stabilisation of water(l) is less than and for others more than in the case where the thermodynamic properties of the aqueous solution are ideal. In one approach this pattern is accounted for in terms of hydrate formation. Alternatively the pattern is analysed in terms of the dependence of practical osmotic coefficients on the composition of the aqueous solution and then in terms of solute-solute interactions. For salt solutions the dependence of the activity of water on salt molalities is compared with that predicted by the Debye-Hückel limiting law. The analysis is extended to consideration of the activities of water in binary aqueous mixtures. The dependence on mole fraction composition of the activity of water in binary aqueous mixtures is examined. Different experimental methods for determining the activity of water in aqueous solutions are critically reviewed. The role of water activity is noted in a biochemical context, with reference to the quality, stability and safety of food and finally with regard to health science. 相似文献
22.
The conclusions recently summarised by A. Marmur [J. Am. Chem. Soc. 122 (2000) 2120] concerning hydrophobic aggregation of solutes in aqueous solution are examined. The thermodynamic analysis is critically reviewed and the impact of implicit extrathermodynamic assumptions discussed. These assumptions are questioned and shown to lead to a model for hydrophobic aggregation which is flawed. 相似文献
23.
The Stern-Volmer quenching constant for the quenching of anthracene fluorescence by bromide at 298.15 K shows a complex dependence on alcohol mole fraction in water plust-butyl alcohol mixtures. A similar pattern is observed at other temperatures except near 285 K, the Lumry temperature for aqueous systems. 相似文献
24.
Michael J. Blandamer John Burgess Stephen J. Hamshere Paul Wellings 《Transition Metal Chemistry》1979,4(3):161-163
Summary Rate constants are reported and discussed for the reaction of [Au(Et4dien)Cl]2+ with HN3 (pH = 1) and of [Au(Et4dien-H)Cl]+ with N
3
–
(pH = 7) in several binary aqueous solvent mixtures. 相似文献
25.
Michael J. Blandamer Elizabeth Godfrey Jill R. Membrey 《Journal of solution chemistry》1974,3(12):881-887
A treatment which predicts the solubilities of gases in solvent mixtures is examined in the context of the analysis of kinetic data for reactions in aqueous mixtures. The treatment is qualitatively successful to some extent in resolving the effects of changes in the initial state of the reacting substrate in the activation parameters. 相似文献
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28.
The nature of rate-retarding effects of cationic micelles on the water-catalyzed hydrolyses of a series of para-substituted 1-benzoyl-1,2,4-triazoles (1a-f) and 1-benzoyl-3-phenyl-1,2,4-triazole (2) has been studied using kinetic methods. A comparison is drawn between medium effects in the micellar Stern region and in model solutions for the micellar Stern region. Simple model solutions involving concentrated aqueous solutions of a small ionic molecule resembling the surfactant headgroup, as reported before,(1) were improved. New model solutions for alkyltrimethylammonium bromide micelles contain both tetramethylammonium bromide (TMAB), mimicking micellar headgroups, and 1-propanol, mimicking hydrophobic tails. The rate-retarding effect of micelles on the hydrolysis of 1a-f and 2 is caused by the high concentration of headgroups as well as by hydrophobic tails in the Stern region where 1a-f and 2 bind to the micelle. Individual contributions of these interactions are quantified. Rate-retarding effects found for different probes, with different sensitivities for interactions as they occur when the probe binds to the micellar Stern region, as well as the micellar Stern region's micropolarity as reported by the E(T)(30) probe, are satisfactorily reproduced by new model solutions containing both TMAB and 1-propanol. 相似文献
29.
Francisco Sanchez Maria J. Nasarre Maria M. Graciani Ragael Jimenez Maria L. Moya John Burgess Michael J. Blandamer 《Transition Metal Chemistry》1988,13(2):150-154
Summary Rate constants are reported for the oxidation by peroxodisulphate ions of octacyanomolybdate(IV) in concentrated aqueous salt solutions containing up to 6 mol dm–3 salt including mixed salt solutions. The dependence of the logarthm of rate constant on salt concentration is discussed in terms of ionic hydration enthalpies and B-viscosity coefficients. The analysis confirms that ion-pairs play a key role in determining reactivities in these systems. 相似文献
30.
Michael J. Blandamer John Burgess Ezz-Eldin A. Abu-Gharib 《Transition Metal Chemistry》1984,9(5):193-197
Summary We report solubilities of a number of cobalt(III) and chromium(III) complex salts in methanol-water mixtures. From these, and published solubilities of salts of other complexes of these metals, we have calculated transfer chemical potentials from water into aqueous methanol for a variety of cationic and anionic complexes of cobalt(III) and chromium(III), using the assumption m(Ph4As+) + m(BPh
4
–
). The established trends are discussed in terms of electrostatic factors and of the hydrophilicity or hydrophobicity of the ligands present. The effects of single ion assumptions on conclusions of initial state-transition state analyses of solvent effects on reactivity are assessed with particular reference to aquation of thetrans-[Co(en)2Cl2]+ andtrans-[Co(py)4Cl2]+ cations.On leave from the Faculty of Science, Sohag, Egypt. 相似文献