Local and full equilibrium

Following Zeldovich and Ovchinnikov [35], let us consider the role of reactant diffusion in establishing equilibrium in a reversible A B -t- B reaction. In terms of formal kinetics, it is described by the equations 

Its steady-state solution (2.1.49) obeys the law of mass action 

Let us consider a hypothetical experiment assume that particles A are kept at such a low temperature that there is no dissociation and the fluc-tuational distribution in a system obeys (2.1.42). Then the reaction volume is monotonously heated up to the temperature when dissociation begins to occur and the dependence ub = nB(t) is monitored. According to (2.1.49), the approach to equilibrium is exponential, i.e.. 

However, this passage in fact involves several stages. At the first stage a system strives to a local equilibrium 

Let us divide the whole volume into blocks with a distinctive size Id as it is shown in Fig. 2.7. Denote an average over block volume by a bar  

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