Chemical Formulas and Stoichiometric Coefficients

The first step in analyzing any engineering problem is to define the system and select the framework for solving the problem. This step is commonly referred to 

Each chemical formula represents a given amount of mass. For example. Reaction 

1 represents 44 units of mass. Reaction 2.2.2 represents 88 units of mass, and Reaction 2.2.3 represents 880 units of mass. We select one of these chemical formulas and relate all relevant quantities (heat of reaction, rate of reaction, etc.) to it. 

We adopt common conventions concerning chemical reactions. Each chemical reaction has an arrow indicating (he direction of the chemical transformation and clearly defines the reactants and products of the reaction. Species to the left of the arrow are called reactants, and those on the right are called products. Reversible reactions are treated as two distinct reactions, one forward and one backward. The arrow also serves as an equality sign for the total mass represented by tbe chemical formula. Thus, each chemical reaction should be balanced an unbalanced chemical reaction violates the conservation of mass principle. 

Once the specific chemical formula is selected, the stoichiometric coefficients of the individual species are defined as follows For each product species, the stoichiometric coefficient is identical to the coefficient of that species in the chemical formula. For each reactant, the stoichiometric coefficient is the negative value of the coefficient of that species in the chemical reaction. If a species does not participate in the reaction, its stoichiometric coefficient is zero. 

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