stoichiometry
/ stoy-kee-OM-eh-tree /
Baking a cake follows a recipe: two eggs and one cup of flour make one cake — not one and a half, not three. Chemical reactions follow recipes too, and stoichiometry is the bookkeeping of those fixed proportions.
Stoichiometry is the quantitative relationship between the amounts of reactants and products in a reaction, read straight from the coefficients of the balanced equation. Those coefficients are ratios of moles, telling you how many particles of each substance combine and form.
It is the backbone of quantitative chemistry: it lets you predict how much product a reaction can yield, how much reactant you must supply, and how a titration's volume converts into an unknown concentration. The discipline rests on conservation of mass — atoms are only rearranged, never created or destroyed.
In 2 H₂ + O₂ → 2 H₂O, the coefficients say two moles of hydrogen react with one mole of oxygen to give two moles of water — a fixed 2:1:2 ratio no matter the batch size.
Balanced-equation coefficients are mole ratios.
Stoichiometric ratios only work when the equation is correctly balanced and the reaction actually goes to completion as written; side reactions and incomplete conversion break the neat arithmetic.