Stoichiometry is the mathematics behind the science of chemistry. Using known physical laws such as the law of conservation of mass and the law of definite proportions, stoichiometry is used to gather information about the amounts of various elements used in a chemical reaction, and whether they took the form of gases, solids, or liquids. Using mathematics, someone can determine the quantities of particular elements needed to create a desired reaction, or the quantities used in the generation of a reaction which has already occurred.
Beginning chemistry classes typically include an introduction to stoichiometry, in which students are asked to balance chemical equations on their homework in and class. Stoichiometry relies on the fact that elements behave in predictable ways, and that matter cannot be created or destroyed. Therefore, when elements are combined to create a reaction, something known and specific will happen, and the outcome of the reaction can be predicted on the basis of the elements and quantities involved.
Chemists look at both the reactants and their products, which can include a new chemical compound along with remainders. In a simple example of stoichiometry, oxygen and hydrogen gases combine to create water, but only in set amounts. Given a set quantity of water, a chemist can determine how much oxygen and water went into the reaction that created the water, using stoichiometry and a knowledge of basic chemistry. Chemists working in the lab can also determine the amount of various products needed to create a particular reaction before they embark on an experiment.
One of the underpinnings of stoichiometric calculations is that amounts have to remain constant. One cannot pull elements out of thin air, and therefore an equation will be unbalanced if one side contains more than the other. Chemists use a unit of measurement called the mole to measure mass in stoichiometry, and when they balance equations, they make sure that both sides are equal, even if the chemical reaction produced a new chemical compound.
While stoichiometric calculations may seem like the purview of scientists alone, people actually utilize stoichiometry every day, although they may not be aware of it. Bakers, for example, rely heavily on the principles of chemistry and the need for balancing ingredients, and they use the known properties of the “elements” they work with to create a balanced equation: a recipe which will have a positive outcome. Stoichiometry is also used in a number of industries, ranging from oil refining to hair dye production.