Linear phenomenological laws chemical reactions

In this section we shall look at the meaning of linear phenomenological laws in the context of chemical reactions. In a formalism in which the principle of detailed balance or microscopic reversibility is incorporated through the condition that forward rates of every elementary step balance the corresponding reverse rate, the Onsager reciprocity is implicit. No additional relations can be derived for the reaction rates if it is assumed that at equilibrium each elementary step is balanced by its reverse. Therefore, the main task in this section will be to relate the Onsager coefficients Ly and the experimentally measured reaction rates. In our formalism the Onsager reciprocal relations will be automatically valid. 

We have seen that the linear phenomenological laws are valid for chemical reactions with affinity A if the condition A/RT 1 is satisfied. However, if the overall chemical reaction... 

Though we considered a coupled set of unimolecular reactions (16.5.24) to obtain (16.5.31), the result is more generally valid. Thus, the linear phenomenological law is valid for an overall chemical reaction if A/RT 1... 

In this Sect.4.9 we discuss Eqs. (4.156), (4.171) concerning chemical reactions in a regular linear fluids mixture (see end of Sect. 4.6), i.e. with linear transport phenomena. This model gives the (non-linear) dependence of chemical reaction rates on temperature and densities (i.e. on molar concentrations (4.288)) only (4.156), which is (at least approximately) assumed in classical chemical kinetics [132, 157]. Here, assuming additionally polynomial dependence of rates on concentrations, we deduce the basic law of chemical kinetics (homogeneous, i.e. in one fluid (gas, liquid) phase) called also the mass action law of chemical kinetics, by purely phenomenological means [56, 66, 79, 162, 163]. 

The balance equations [APP 64] enable us to estabhsh the entropy production rate, from which we deduce the form of the phenomenological relations by way of linearized TIP. Note that with regard to the chemical reactions, there is no need to linearize the stem, because the hterature generally gives us nonlinear chemical kinetic laws with known coefficients (the specific reaction rates). In addition, the balance laws give us the system of equations to be solved in order to determine the fields of variables characterizing the evolution of the plasma in space and time, by means of the knowledge of the physical coefficients. Here, we shall assume steady-state one-dimensional evolution. 

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