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Encounter equilibria

The value of the equilibrium constant for an encounter is certainly of prime importance in the discussion of interchange pathways of complex formation. This was first suggested, in fact by Werner [4] as early as in 1912. Most of the work on ligand substitution in complexes is based on the assumption that encounter equilibria could be calculated from the ion-pairing equation of Fuoss [5] which was derived in turn from a consideration of diffusion-controlled reactions by Eigen [6]. At zero ionic strength, the encounter equilibrium constant, Kp is given as... [Pg.488]

Whenever it is feasible, it is useful to study encounter equilibria experimentally, as in the case of Co(III) complexes in water and non-aqueous solvents [7]. There are some weaknesses in equation (7.3) as evidenced by (i) the formation of anionic species by overcompensation of the original positive charge of the metal complex, (ii) lack of evidence of outer-sphere complexation in some cases like Co(en)j+ with Fe(CN) - and (iii) the fact that outer-sphere complexes are preferred over inner-sphere complexes in several systems. [Pg.488]

Solvent Resistance. At temperatures below the melting of the crystallites, the parylenes resist all attempts to dissolve them. Although the solvents permeate the continuous amorphous phase, they are virtually excluded from the crystalline domains. Consequently, when a parylene film is exposed to a solvent a slight swelling is observed as the solvent invades the amorphous phase. In the thin films commonly encountered, equilibrium is reached fairly quickly, within minutes to hours. The change in thickness is conveniently and precisely measured by an interference technique. As indicated in Table 6, the best solvents, specifically those chemically most like the polymer (eg, aromatics such as xylene), cause a swelling of no more than 3%. [Pg.439]

We have encountered equilibrium before—in our we considered the liquid-gas equilibrium that consideration of phase changes. In Section 5-1.2 fixes the vapor pressure of a liquid, and in Sec-142... [Pg.142]

Perhaps the most commonly encountered equilibrium reactions are those involving water as a reactant or product. Driving such equilibria by using excess water (e.g. hydrolysis reactions) is easy, but driving equilibria by removing water (e.g. in ester or acetal formation) can be more difficult. An excellent device for the continuous removal of water from a reaction mixture is the Dean-Stark trap (Fig. 9.27). [Pg.169]

We will encounter equilibrium calculations of solution and gaseous species in Chapter 2 1, Electrochemistry. ... [Pg.739]

The function/(Q represents any sorption isotherm for a chemical species (linear or nonlinear). The most frequently encountered equilibrium sorption models are listed in Table 6.1 (Simimeket. al., 1999 Selim et. al. 1990)... [Pg.98]

We will encounter equilibrium calculations for solution and gaseous species In electrochemistry (see Chapter 21). [Pg.696]

When you encounter equilibrium questions on examinations, use your mental model as you develop a written answer. Imagine the scenario posed in the question and give a written description of what you see happening in your mind. [Pg.431]

The reason for this enliancement is intuitively obvious once the two reactants have met, they temporarily are trapped in a connnon solvent shell and fomi a short-lived so-called encounter complex. During the lifetime of the encounter complex they can undergo multiple collisions, which give them a much bigger chance to react before they separate again, than in the gas phase. So this effect is due to the microscopic solvent structure in the vicinity of the reactant pair. Its description in the framework of equilibrium statistical mechanics requires the specification of an appropriate interaction potential. [Pg.835]

Most chemically reacting systems tliat we encounter are not tliennodynamically controlled since reactions are often carried out under non-equilibrium conditions where flows of matter or energy prevent tire system from relaxing to equilibrium. Almost all biochemical reactions in living systems are of tliis type as are industrial processes carried out in open chemical reactors. In addition, tire transient dynamics of closed systems may occur on long time scales and resemble tire sustained behaviour of systems in non-equilibrium conditions. A reacting system may behave in unusual ways tliere may be more tlian one stable steady state, tire system may oscillate, sometimes witli a complicated pattern of oscillations, or even show chaotic variations of chemical concentrations. [Pg.3054]

Two other types of equilibrium curves are occasionally encountered with the system of two components forming a continuous series of solid solutions. These are shown in Figs. 1,16, 3 and 1,16, 4. In the former the freezing or melting curve passes through a minimum (examples p-chloroiodobenzene, m.p. 57° - p-dichlorobenzene, m.p. 53° naphtha-... [Pg.34]

Numerous attempts to determine the equilibrium constants using titration microcalorimetry failed, due to solubility problems encountered at the higher concentrations of catalyst and dienophile that are required for this technique. [Pg.73]

For the nitration of the very weak base, acetophenone, there is reasonable agreement between observed and calculated activation parameters, and there is no doubt that nitration of the free base occurs at acidities below that of maximum rate. In this case the equilibrium concentration of free base is much greater than in the examples just discussed and there is no question of reaction upon encounter. ... [Pg.159]

In any equilibrium process the sequence of intermediates and transition states encountered as reactants proceed to products m one direction must also be encountered and m precisely the reverse order m the opposite direction This is called the principle of microscopic reversibility Just as the reaction... [Pg.249]

In the equilibrium treatment of precipitation, however, the reverse reaction describing the dissolution of the precipitate is more frequently encountered. [Pg.139]

Anhydride manufactured by acetic acid pyrolysis sometimes contains ketene polymers, eg, acetylacetone, diketene, dehydroacetic acid, and particulate carbon, or soot, is occasionally encountered. Polymers of aHene, or its equilibrium mixture, methylacetylene—aHene, are reactive and refractory impurities, which if exposed to air, slowly autoxidize to dangerous peroxidic compounds. [Pg.79]

The N equations represented by Eq. (4-282) in conjunction with Eq. (4-284) may be used to solve for N unspecified phase-equilibrium variables. For a multicomponent system the calculation is formidable, but well suited to computer solution. The types of problems encountered for nonelectrolyte systems at low to moderate pressures (well below the critical pressure) are discussed by Smith, Van Ness, and Abbott (Introduction to Chemical Engineering Thermodynamics, 5th ed., McGraw-Hill, New York, 1996). [Pg.536]

The results of the analyses for all the various elements commonly encountered in distillation processes are summarized in Table 13-5. Details of the analyses are given by Smith (Design of Equilibrium Stage Processes, McGraw-Hul, New York, 1967) and in a somewhat different form by Henley and Seader (op. cit.). [Pg.1261]

Except as an index of respiration, carbon dioxide is seldom considered in fermentations but plays important roles. Its participation in carbonate equilibria affects pH removal of carbon dioxide by photosynthesis can force the pH above 10 in dense, well-illuminated algal cultures. Several biochemical reactions involve carbon dioxide, so their kinetics and equilibrium concentrations are dependent on gas concentrations, and metabolic rates of associated reactions may also change. Attempts to increase oxygen transfer rates by elevating pressure to get more driving force sometimes encounter poor process performance that might oe attributed to excessive dissolved carbon dioxide. [Pg.2139]

Figure 9 is the VLE plot for a binary mixture that has essentially a uniform equilibrium, and therefore represents a relatively easy separation. However, there are many cases where non-ideal separations are encountered. These more difficult distillations are defined by the examples shown in Figure 10. [Pg.173]

Diols that bear two hydroxyl groups in a 1,2 or 1,3 relationship to each other yield cyclic acetals on reaction with either aldehydes or ketones. The five-membered cyclic acetals derived from ethylene glycol (1,2-ethanediol) are the most commonly encountered examples. Often the position of equilibrium is made more favorable by removing the water fomned in the reaction by azeotropic distillation with benzene or toluene ... [Pg.722]

A frequently encountered pH-rate profile exhibits a bell-like shape or hump, with two inflection points. This graphical feature is essentially two sigmoid curves back-to-back. By analogy with the earlier analysis of the sigmoid pH-rate curve, where the shape was ascribed to an acid-base equilibrium of the substrate, we find that the bell-shaped curve can usually be accounted for in terms of two acid-base dissociations of the substrate. The substrate can be regarded, for this analysis, as a dibasic acid H2S, where the charge type is irrelevant we take the neutral molecule as an example. The acid dissociation constants are... [Pg.285]


See other pages where Encounter equilibria is mentioned: [Pg.259]    [Pg.240]    [Pg.127]    [Pg.485]    [Pg.201]    [Pg.686]    [Pg.1297]    [Pg.1917]    [Pg.453]    [Pg.32]    [Pg.229]    [Pg.640]    [Pg.340]    [Pg.50]    [Pg.407]    [Pg.271]    [Pg.53]    [Pg.1673]    [Pg.3]    [Pg.127]    [Pg.132]    [Pg.5]    [Pg.199]    [Pg.264]    [Pg.562]    [Pg.626]   
See also in sourсe #XX -- [ Pg.488 ]




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