Real versus Model Equilibrium

It seems clear from this discussion that the question of whether any particular real system had reached equilibrium or not can only be answered in relation to the purposes 

So why are we devoting so much discussion to such a small point The reason will gradually become apparent. This topic is simply the first one in which the distinction between the thermodynamic model and the real world arises. The fact that real systems do achieve equilibrium tends to lead to the conclusion that thermodynamics refers to, or even is part of, real systems, and this inevitably leads to confusion with respect to reversible processes, infinitesimals, choice of components, and many other parts of the model. Our point of view is that real systems achieve the kind of practical equilibrium we defined in 3.3, including local and partial equilibria, but that the thermodynamic model uses idealized equilibrium states. If there is not too much difference between them, then the model results are useful in the real world. The definition of too much difference depends on the application. 

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