Reaction Stoichiometry refers to the examination of the relative abundances of reactants and products in a chemical reaction within a defined system. In order to use reaction stoichiometry to calculate desired quantitative data, it is important to first understand the relationships between the reactants and the products. This requires the process of balancing reactions, which is usually the most important step when doing stoichiometric calculations.
To balance an equation, it is necessary that there are the same number of atoms in the reactants as there are in the products. One can do this by raising the coefficients of individual reactants or products.
For example, the combustion of methane involves reacting methane (CH4) and oxygen (O2) to form carbon dioxide (CO2) and water (H2O). The unbalanced chemical equation can be written as:
CH4(g) + O2(g) --> CO2(g) + H2O(l)
It can be seen that the number of atoms on each side are unbalanced; and so raising the coefficients of O2 and H2O to 2 will balance the equation for the combustion reaction:
CH4(g) + 2O2(g) --> CO2(g) + 2H2O(g)
Thus, from these stoichiometric coefficients, it can be seen that 1 mole of methane reacts with 2 moles of molecular oxygen to form 1 mole of carbon dioxide and 2 moles of water. Using these relative ratios, one can hypothetically say that 0.1 moles of methane requires 0.2 moles of oxygen or 0.6 moles of methane requires 1.2 moles of oxygen. Therefore, understanding the relationship between reactants and products is absolutely fundamental to run stoichiometric calculations on chemical reactions.