How To Calculate The Percent Yield and Theoretical Yield

The video introduces the concepts of theoretical and percent yield, starting with an example problem involving iron reacting with oxygen to produce iron oxide. The first step in solving such problems is to write a balanced chemical equation.

To calculate the theoretical yield, which is always the maximum amount of product that can be formed, the grams of the limiting reactant are converted into moles, then to moles of the product using the molar ratio from the balanced equation, and finally back to grams of the product. The formula for the molar mass of Fe3O4 is calculated (231.55 g/mol). The theoretical yield for the example is calculated to be 62.5 grams of Fe3O4.

The percent yield is calculated using the formula: (Actual Yield / Theoretical Yield) * 100. The actual yield is the amount of product given in the problem (58.1 grams in this case). Using the calculated theoretical yield of 62.5 grams, the percent yield is found to be roughly 93%.

This section explains how to find the actual yield if the percent efficiency (percent yield) is given. If a reaction is 75% efficient, the actual yield is 75% of the theoretical yield. This can be calculated by multiplying the theoretical yield (62.5 g) by the decimal equivalent of the percentage (0.75), resulting in 46.9 grams of iron oxide.

A new problem is introduced with two reactants, vanadium and ozone, where both reactant amounts are given, requiring the identification of the limiting reactant. The balanced chemical equation for the reaction of vanadium with ozone to produce vanadium(V) oxide (V2O5) is established. The process involves calculating the theoretical yield for each reactant individually, and the lower of the two results will be the true theoretical yield, indicating the limiting reactant.

The theoretical yield is calculated for both 50 grams of vanadium and 50 grams of ozone reacting to produce V2O5. For vanadium, the theoretical yield is 89.26 grams of V2O5. For ozone, the theoretical yield is 113.675 grams of V2O5. Since 89.26 grams is the lower value, vanadium is identified as the limiting reactant, and 89.26 grams is the true theoretical yield.

Using the theoretical yield of 89.26 grams of V2O5 and the actual yield of 65 grams (given in the problem), the percent yield for the second example is calculated. The percent yield for this process is 72.8%.

If the process was 90% efficient, the actual yield of vanadium oxide would be 90% of the theoretical yield (89.26 grams). This calculation yields 80.334 grams of vanadium oxide. The video concludes by summarizing the methods for calculating theoretical yield, percent yield, and actual yield when given percent efficiency.