How can you determine the percent yield of a reaction?

• A. Percent yield is defined as actual yield divided by theoretical yield, multiplied by 10.
• B. Percent yield is defined as the theoretical yield divided by the actual yield, multiplied by 100.
• C. Percent yield is defined as the actual yield minus the theoretical yield (absolute value) multiplied by 100.
• D. Percent yield is defined as (Actual yield / Theoretical yield) × 100%.

Answer: (D)

Percent yield tells you how efficient a reaction was by comparing the actual amount of product you recovered to the theoretical maximum predicted by stoichiometry. To determine it, you need the actual yield (the mass or moles of product you isolated after purification) and the theoretical yield (the amount of product predicted from the balanced equation using the limiting reagent). Convert the starting amounts to moles, identify which reactant limits the product, and then convert that amount of product to the same units as your actual yield. The percent yield is (actual yield ÷ theoretical yield) × 100%. For example, if the theoretical yield is 2.0 g and you actually obtain 1.5 g, the percent yield is 75%. Values are usually below 100%, though a value over 100% can indicate impurities or measurement errors.