Phase equilibrium with equal pressure in all phases

1 Phase equilibrium with equal pressure In all phases 

This criterion for chemical equilibrium in a two-phase system then requires that the chemical potential of any species 1 should be uniform and constant through the separator. 

If the closed separator has more than two phases or two regions, a criterion for chemical equilibrium can be derived by considering any two of the phases or regions, say 7j and 72, at a time. The relation 

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