To find the theoretical yield, balance the given chemical equation, and find the limiting reagent by calculating the mole ratios. Once the limiting reagent is found, convert its amount from moles to grams.
- Balance the given chemical equation
The number of reactants and products on each side of an equation must be equal. For example, the chemical equation H2 + O2 --> H2O must be balanced by placing a stoichiometric coefficient of two in front of H2 and H2O, so it becomes 2H2 + O2 --> 2H2O.
- Convert the reactants to moles
Convert the reactants to moles by dividing the amount of the reactant in grams by the reactant's molar mass in grams per mole. If the amount of given hydrogen is 6 grams and the amount of given oxygen is 2 grams, the result is 6 moles of H2 and 0.125 moles of O2.
- Determine the limiting reagent
Multiply both of the reactants by the ratio of the reactants' and product's stoichiometric coefficients. Since the coefficients for both H2 and H2O are two, 6 moles of H2 produces 6 moles of H2O. However, O2 and H2O have coefficient ratio of 2 to 1, so 0.125 moles of O2 produces 0.25 moles of H2O. O2 is the limiting reagent since 0.25 moles is less than 6 moles.
- Find theoretical yield
Convert the amount of the limiting reagent by the molar mass of the product to convert it to grams. Since the molar mass of H2O is 18 grams per mole, the theoretical yield of H2O is 4.5 grams.