The Representation and Calculus of Composition Changes

To each atomic species there belongs a real number called its atomic weight, a,. The molecular weight of the species sis is given by 

The chemical meaning of the equation assfs = 0 is that the changes in the number of moles during the reaction 01 are in the ratios of the stoicheiometric coefficients, i.e. Anslots is independent of s. Therefore we may define a continuous variable belonging to a reaction as follows  

Definition 4. The extent of the reaction 01 is a variable f, such that the composition changes by reaction are Ans = as . The extent per unit volume, i, is similarly defined by 

Remark 11. For simultaneous reactions an extent can be defined for each reaction and 

Theorem 5. The composition changes of a system under the set of reactions 0tr, r = 1, 2,. .., r, can be fully described by the subset of independent reactions. 

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