Stoichiometry: definition in chemistry
Stoichiometry: The calculation of the quantities of reactants and products in chemical reactions, based on the mole ratios in a balanced equation.
A balanced equation shows how many moles of each substance react or form, such as the 2 : 1 : 2 ratio in 2H₂ + O₂ → 2H₂O. By converting masses to moles, applying the ratio and converting back, chemists can predict how much product a reaction will give or how much reactant is needed. Stoichiometry is also used to find the limiting reactant and to calculate percentage yield. The word comes from the Greek for element and measure.
Examples
- 16 g of methane burns to give 44 g of carbon dioxide
- 4 g of hydrogen reacts with 32 g of oxygen to form 36 g of water
- Airbags inflate as 2NaN₃ → 2Na + 3N₂ releases nitrogen gas
- Working out how much baking soda will neutralize a spilled acid
On the periodic table
Stoichiometry calculations start from the atomic masses on the periodic table, which are used to convert grams of each substance into moles.