Question

Define: stoichiometry.

Answer 1

Stoichiometry is the measure of the amounts of reactants and products which take part in a chemical reaction or is formed. It is the relative amount of reactant and product.

Complete step by step answer:
Stoichiometry is defined as the exact numbers which indicate the actual proportions of the reactant and product. The relative amount of the reactants are important for calculating the exact amount of individual starting material required for the reaction.
Stoichiometry is important for writing balanced chemical reactions. Thus the ratio of all the reactants and products can be determined.
Stoichiometry is based on the law of conservation of mass. The law of conservation of mass states that the total mass of the reactants is equal to the total mass of the products. This gives the information about the quantities of reactants and products formed in a ratio of positive integers.
If the amount of the all the individual reactants are known the amount of the products is calculated by applying law of conservation of mass. Alternatively, if the amount of the product is known and one reactant has a known quantity then the amount of the other reactants is also calculated using the balanced chemical equation.
Let us take an example illustrating the stoichiometry of a reaction. The combustion of methane in presence of oxygen produces carbon dioxide and water. The balanced chemical equation for the reaction is
$C{H_4} + 2{O_2} \to C{O_2} + 2{H_2}O$
From the above reaction it is evident that one mole of methane gas requires two moles of oxygen to produce one mole of carbon dioxide and two moles of water. The stoichiometry for the reactants is $1:2$ and the stoichiometry of the product is $1:2$.

Note:
Stoichiometry is useful in order to assure that all the reactants get consumed. None of the reactants remained after completion of the reaction. The opposite of stoichiometric amount is catalytic amount.