Percent Yield Section 12.4

Why don’t chemical reactions always produce the theoretical amount? -Reactants are contaminated with other substances Some reactants evaporate Some reactants stick to surfaces of containers Sometimes chemical reactions stop before all the chemicals are used up Therefore, chemists utilize a value to determine how much product is actually produced called percent yield.

Calculating Percent Yield Stoichiometry is used to determine the theoretical yield – the maximum amount of a product a chemical reaction can produce. Next, the chemical reaction is carried out in and experiment and the amount of product that is produced is called the actual yield. The percent yield equals the actual yield divided by the theoretical yield times 100. Percent Yield = Actual Yield x 100 Theoretical Yield

Percent Yield Practice I 1. A student uses stoichiometry to calculate the actual yield of CO2 in an equation as 323 g. When the student mixes the chemicals to make the CO2, he finds that the reaction only produced 308 g of CO2. What was the % yield?

Percent Yield Practice I 2. K + B2O3  K2O + B In the above reaction, how many grams of potassium oxide can be produced with 78 grams of potassium and 140 grams of boron oxide? If the actual yield from the above reaction was 84 grams, what is the percent yield?

Percent Yield Practice I 3. N2 + H2  NH3 The actual yield in the above reaction was 42 grams of ammonia using 84 grams of nitrogen and 8 grams of hydrogen. What is the % yield?