% Yield

% yield compares the amount of product you actually obtain from an experiment with the amount that theoretically could have been obtained had every molecule of the limiting reactant been used to make product. It is defined as:

% yield = 100% (#moles product obtained) / max. #moles product possible

The yield can vary from 0% (no product obtained) to 100% (theoretically, the maximum amount possible).

To calculate “% yield” you must know:

  • the stoichiometry of the reaction
  • the identity and amount (in moles) of the limiting reactant
  • the amount (in moles) of product obtained

Most reactions give one molecule of product for every molecule of reactant. If this is the case, the maximum number of moles of product that can be obtained is identical to the number of moles of limiting reactant used (call this R). If you obtain only P moles of product, then:

% yield = (P / R) x 100%

Some reactions give one molecule of product for every two molecules of limiting reactant. In this case, the yield is defined as:

% yield = (2P / R) x 100%