12
Stoichiometry II: Calculations Based
on Chemical Equations
A chemical equation is a statement of experimental fact. It gives on the left side
the reactants and on the right side the products of the reaction. Because no
atoms are produced or destroyed in a nonnuclear chemical reaction, the equation must be so balanced that every atom originally present in the reactants is
accounted for in the products. This means that the combined weight of the
reaction products is exactly equal to the combined weight of the original
reactants.
All of the important stoichiometric calculations that relate the weights and
volumes of starting materials to the weights and volumes of products typically
involve just three simple steps.
1. Find how many moles correspond to the given quantity of some substance in the reaction.
2. Use the balanced chemical equation to find, from the number of moles
of the given substance, the number of moles of the substance sought in
the calculation.
3. Convert the number of moles of the substance sought to the units
requested in the statement of the problem.
?hese three steps are illustrated in the following problems.