Reaction Stoichiometry and Its Significance

For a complex system, determination of the stoichiometry of a reacting system in the form of the maximum number (R) of linearly independent chemical equations is described in Examples 1-3 and 14. This can be a useful preliminary step in a kinetics study once all the reactants and products are known. It tells us the minimum number (usually) of species to be analyzed for, and enables us to obtain corresponding information about the remaining species. We can thus use it to construct a stoichiometric table corresponding to that for a simple system in Example 2-4. Since the set of equations is not unique, the individual chemical equations do not necessarily represent reactions, and the stoichiometric model does not provide a reaction network without further information obtained from kinetics. 

Spencer and Pereira (1987) studied the kinetics of the gas-phase partial oxidation of CH4 over a Mo03-Si02 catalyst in a differential PFR. The products were HCHO (formaldehyde), CO, C02, and H20. 

Using manipulations by hand or Mathematica as described in Example 1-3, we obtain the following set of 3 (R) equations in canonical form with CH4, 02, and H20 as components, and CO, C0 and HCHO as noncomponents  

These chemical equations may be combined indefinitely to form other equivalent sets of three equations. They do not necessarily represent chemical reactions in a reaction network. The network deduced from kinetics results by Spencer and Pereira (see Example 5-8) involved (3), (1)—(3), and (2) as three reaction steps. 

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