What is Stoichiometry?
Stoichiometry is the quantitative description of the proportions by moles of the substances in a chemical reaction.

When doing experiments, it is unscientific and dangerous to mix chemicals in a haphazard manner.  Before any practical laboratory work is done, chemists almost always start with a balanced reaction equation. This is true for a reaction that we know works, or for one that we predict works.  A balanced equation helps tell the reaction's stoichiometry.

The stoichiomentry of a reaction is the description of the relative quantitites by moles of the reactants and products as they appear by the coefficients of the balanced equation.  Stoichiometry is the molar bookkeeping of chemistry, and in nature the books must balance.  Quantitative information is only available through its stoichiometry.  This applies to the pure study of chemistry, but also to the uses of chemistry in a wide variety of fields such as agriculture, clinical analysis, pharmaceuticals, food chemistry, inhalation therapy, nutrition, forensic science, geochemistry and the list can go on and on.  The work begins with the writing and balancing of an equation, because this is the work that gives the coefficients - the numbers that disclose the proportions by mole.