Molar reaction quantities in general

Now let us generalize the relations of the preceding section for any chemical process in a closed system. Suppose the stoichiometric equation has the form 

The amount of reactant or product species i present in the closed system at any instant depends on the advancement at that instant, and is given by 

Thermodynamics and Chemistry, second edition, version 3 2011 by Howard DeVoe. Latest version www.chem.umd.edu/thermobook 

The infinitesimal change in the amount due to an infinitesimal change in the advancement is 

In an open system, the total differential of extensive property X is 

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