Use → or -> or = for the reaction arrow
moles = mass ÷ molecular weight
moltarget = molknown × (coeftarget ÷ coefknown)
Disclaimer
Results assume complete reaction and ideal laboratory conditions unless yield is specified. Always verify calculations for critical applications.
Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions. The word comes from the Greek words "stoicheion" (element) and "metron" (measure). It allows chemists to predict how much product will form from given amounts of reactants, or how much of a reactant is needed to produce a desired amount of product.
At its core, stoichiometry is based on the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. This means the total mass of reactants must equal the total mass of products. By using balanced chemical equations and molar relationships, stoichiometry enables precise calculations essential for laboratory work, industrial processes, and research.
The mole is the fundamental unit in stoichiometry. One mole contains exactly 6.022 × 10²³ particles (Avogadro's number) of a substance, whether atoms, molecules, or ions. The molar mass of a substance (in grams per mole) is numerically equal to its molecular or atomic weight.
Mass to Moles
To convert mass to moles, divide the mass (in grams) by the molar mass of the substance.
Moles to Mass
To convert moles to mass, multiply the number of moles by the molar mass of the substance.
A balanced chemical equation provides the mole ratios between all substances in a reaction. The coefficients in front of each formula represent the relative number of moles of each substance. For example, in the equation 2H₂ + O₂ → 2H₂O, the mole ratio of H₂ to O₂ to H₂O is 2:1:2.
These ratios are the key to stoichiometric calculations. Once you know the moles of one substance, you can use the mole ratio to find the moles of any other substance in the reaction. This is why balancing equations correctly is essential - an unbalanced equation will give incorrect mole ratios and therefore incorrect calculations.
The theoretical yield is the maximum amount of product that could be formed based on stoichiometric calculations, assuming the reaction goes to completion with no losses. However, in practice, reactions rarely achieve 100% yield due to factors like incomplete reactions, side reactions, loss during transfer, and purification losses.
Percent Yield Formula:
% Yield = (Actual Yield ÷ Theoretical Yield) × 100
Understanding yield is crucial for industrial chemistry where efficiency directly impacts costs. A reaction with 80% yield means 20% of the potential product is lost, which can be significant at large scales.