Pseudo-equilibria, local

During the first part of the induction period (section 6. /), the different components of the reaction interact with one another, moving towards a pseudo-equilibrium under the prevailing conditions of temperature and pressure. In many cases, a visible gel phase is present. In other cases, the same type of material is present as colloidal particles, invisible to the naked eye. A fragment or domain of this amorphous component is shown in Fig. 4(a) as a random network of linked tetrahedra [36]. This amorphous material equilibrates with the cations and anions of the solution phase in such a way that local areas of increased order are created in which the structure begins to resemble that of the eventual product (Fig. 4(b)). 

There is no method for theoretical prediction or correlation of VLE data in reacting systems. It has to be remembered that equilibrium in such systems means not only concentration and thermal equilibrium but also absence of chemical change. In other words, the chemical reaction must also be at equilibrium or, if it is irreversible, it must have reached completion. This poses the question of how to express the interphase concentration driving force in, e.g., a packed column in the presence of, say, a slow reaction. Should it be the difference between the local concentration of a component in the vapour phase and a true equilibrium value corresponding to a given liquid concentration of the corai)onent or should a pseudo equilibrium value, which... 

Figure 5.10 Representation of the formation of the lone pair in the PF3 molecule, (a) An isolated P3 + ion consisting of a P5+ core surrounded by two nonbonding electrons in a spherical distribution, (b) Three approaching F ions distort the distribution of the two valence shell electrons pushing them to one side of the P5+ core, (c) When the F ligands reach their equilibrium positions, the two nonbonding electrons are localized into a lone pair, which acts as a pseudo-ligand giving the PF3 molecule its pyramidal geometry.

Microtubule assembly in cells differs in some ways from assembly in vitro. In cells, nucleation of microtubules requires a third type of tubulin, which is called y-tubulin, that functions in concert with other proteins in the form of a y-tubulin ring complex. In most animal cells, the y-tubuIin ring complex is located at the pericentriolar region of the microtubule organizing center (or centrosome) where it nucleates microtubule assembly at the minus ends (7). The y-tubulin does not become incorporated into the microtubule, but rather it only localizes to the minus ends. Assembly of tubulin to form microtubules during the early stages of polymerization in vitro can be considered a pseudo first-order reaction. A steady state is eventually attained in which both the soluble tubulin concentration and the microtubule polymer mass attain stable plateaus (8). The critical concentration at apparent equilibrium (actually a steady state, see below) is the concentration of soluble tubulin in apparent equilibrium with the microtubule polymers. 

T2 spin-state equilibrium. The two NMR spectra become only similar when the temperature is lowered to 233 K, where iron is essentially in its diamagnetic low-spin state. The localization of Fe" in the pseudo-octahedral site is further confirmed by cyclic voltammetry which shows the [RFe(L36)3] helicates being oxidized in a reversible one-electron process at Ei/2 0.82 V (vs SCE), independent of the nature of the R " ion (Piguet et al., 1997b). 

Fenouillot et ol. [368] reviewed polymer blends with solid nanopartides. The authors briefly discussed oil/water emulsions with solid colloidal partides, considering their wettability and location. Next, polymer blends with nanopartides were discussed, starting with systems near the phase separation, and then within the immiscibility region. Some similarities and differences between the low- and high-viscosity emulsions were highlighted. The particular reason for preparing the review seems to be the authors search for factors that may affect nanoparticle localization at the thermodynamic equilibrium. Diverse polymer blends with pseudo-spherical... 

Here and k°- are pseudo-first-order rate constants (otherwise see (5.3.40)). For very ficist interfacial reactions, local equilibrium may be assumed and... 

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