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Chemical potential reacting species

To every chemical component in a system we can assign a free energy per mole of that species. This quantity is called the chemical potential of species) and is given the symbol p,j. We can view p,j as a property of species), indicating how that species will react to a given change, for example, a... [Pg.57]

The majority of these articles establish equations involving the Gibbs energy of the systems or the chemical potentials of species. Some of those papers have been compiled in recent works [24, 25] that furthermore describe construction for multicomponent and multi-reacting systems, where one of the axes of the diagram represents the potential of one electrode, while the others represent other chemical composition variables. [Pg.1703]

Transfer matrix calculations of the adsorbate chemical potential have been done for up to four sites (ontop, bridge, hollow, etc.) or four states per unit cell, and for 2-, 3-, and 4-body interactions up to fifth neighbor on primitive lattices. Here the various states can correspond to quite different physical systems. Thus a 3-state, 1-site system may be a two-component adsorbate, e.g., atoms and their diatomic molecules on the surface, for which the occupations on a site are no particles, an atom, or a molecule. On the other hand, the three states could correspond to a molecular species with two bond orientations, perpendicular and tilted, with respect to the surface. An -state system could also be an ( - 1) layer system with ontop stacking. The construction of the transfer matrices and associated numerical procedures are essentially the same for these systems, and such calculations are done routinely [33]. If there are two or more non-reacting (but interacting) species on the surface then the partial coverages depend on the chemical potentials specified for each species. [Pg.452]

Thus, given sufEcient detailed knowledge of the internal energy levels of the molecules participating in a reaction, we can calculate the relevant partition functions, and then the equilibrium constant from Eq. (67). This approach is applicable in general Determine the partition function, then estimate the chemical potentials of the reacting species, and the equilibrium constant can be determined. A few examples will illustrate this approach. [Pg.95]

Here m (i = A, B, or AJBW) is the molar chemical potential of reacting species i. Equation 3 is valid for self-associations as well since n or m is zero in that case. Under ideal (theta) solution conditions the activity coefficient ifo of each of the associating species is one, so that... [Pg.267]

There is no change in the chemical composition of the reacting species in reactions (a) and (b) nevertheless, it is possible to measure the rate of these reactions by studying the process of the change in the spin state of the nuclei (ortho-para conversion). Theoretically, reactions (a)-(d) are of special interest because for them rather accurate non-empirical calculations of the potential energy surface, as well as detailed, up to quantum mechanical, calculations of the nuclear dynamics during an elementary reaction act can be carried out. [Pg.51]

In some systems, particularly metal oxides or nitrides, different states of oxidation of the metal or metals could be assumed or actually determined. Expressions for equilibrium constants related to reactions between the atoms in different oxidation states could be set up in terms of the mole fractions of the reacting species. The expressions for the chemical potentials could also be written in terms of these mole fractions. As an example, consider the substance Uj l,Pul02 x. The question might be to determine how the pressure of oxygen varies with the value of x at constant temperature and constant y. We assume that the uranium is all in the oxidation state of +4 and that the plutonium exists in the +3 and +4 oxidation states for positive values of x. The equilibrium change of state is... [Pg.311]

If there is a difference in chemical potential, the transfer of energy occurs as transfer of matter. Chemical potential is a measure of the tendency of the species to leave the phase, to react or to spread throughout the phase through chemical reaction, diffusion, etc. [Pg.137]

In addition to these more practical problems of catalyst preparation, there are also severe theoretical problems associated with the prediction of the chemistry in the fluid state of a compound. The motion of all structural elements (atoms, ions, molecules) is controlled by a statistical contribution from Brownian motion, by gradients of the respective chemical potentials (those of the structural elements and those of all species such as oxygen or water in the gas phase which can react with the structural elements and thus modify the local concentration), and by external mechanical forces such as stirring and gas evolution. In electric fields (as in an arc melting furnace), field effects will further contribute to nonisotropic motion and thus to the creation of concentration gradients. An exhaustive treatment of these problems can be found in a textbook [6] and in the references therein. [Pg.18]

Proof of highly unstable radical intermediates by electrochemiluminescence — A special mechanism of Electrochemiluminescence is observed when both reacting species of the electron transfer are generated simultaneously at the same potential at the same electrode (so-called DC-ECL or ECL with a coreactant). This is possible only when a chemical step is involved in the electrode process of the coreactant (CH). A typical example is the cleavage of its primarily formed ion radical into a stable ion and a strongly reducing or oxidizing... [Pg.219]

Deposition in a PEVD system is accomplished by transporting both (e ) and (A ) across the interfaces at (II), and from (II) to (III) to react with (B) from the sink vapor phase. This is equivalent to the transport of neutral species (A) from (II) to (III) under a chemical potential gradient of (A). Consequently, the chemical... [Pg.111]

Intrapellet transport restrictions can limit the rate of removal of products, lead to concentration gradients within pellets, and prevent equilibrium between the intrapellet liquid and the interpellet gas phase. Transport restrictions increase the intrapellet fugacity of hydrocarbon products and provide a greater chemical potential driving force for secondary reactions. The rate of secondary reactions cannot be enhanced by a liquid phase that merely increases the solubility and the local concentration of a reacting molecule. Olefin fugacities are identical in any phases present in thermodynamic equilibrium thus, a liquid phase can only increase the rate of a secondary reaction if it imposes a transport restriction on the removal of reacting species involved in such a reaction (4,5,44). Intrapellet transport rates and residence times depend on molecular size, just as convective transport and bed residence time depend on space velocity. As a result, bed residence time and molecular size affect chain termination probability and paraffin content in a similar manner. [Pg.256]

Now we discuss how to calculate the equilibrium composition of a reacting non-ideal gas mixture. In order to use Eq. (12.7), we need an expression for the dependence of the chemical potential of each species in the system with its composition. In general, this can be expressed as (see Sec. 11) ... [Pg.86]

Before the model discussed above was published, tha-e were three other suggestions of how to model spatiotemporal dynamics in electrochemical systems. The first attempt at a theoretical description of electrochemical pattern formation came from Jome. His model is based on a chemical instability in the reaction mechanism and only takes into account the concentrations of the reacting species as dependent variables, not the potential. This, of course, means that the model is not applicable to any of the systems exhibiting an electrical instability. This includes the examples treated by Jome, namely, anion reduction reactions or cation reduction in the presence of SCN . Meanwhile, both oscillators are unanimously classified as NDR oscillators [see Section n.2.(ii)] and hence their spatiotemporal description requires a different approach. [Pg.97]


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See also in sourсe #XX -- [ Pg.137 ]




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