Final answer:
The percent yield is found by dividing the actual yield of a product by its theoretical yield and then multiplying by 100%. To calculate the percent yield for the reaction given (PCl3 with excess water), the actual yield of HCl is taken (91.0 g), but additional information is necessary to determine the theoretical yield.
Step-by-step explanation:
The percent yield of a reaction is calculated by dividing the actual yield by the theoretical yield and multiplying by 100%. The actual yield is the amount of product actually obtained from the reaction. In the reaction where phosphorus trichloride (PCl3) reacts with water to form hydrochloric acid (HCl) and phosphorous acid (H3PO3), assuming PCl3 is the limiting reagent, the theoretical yield would be based on the stoichiometry of the balanced chemical equation. Given that 200 grams of PCl3 reacts with excess water, we have to use the molar mass of PCl3 and the molar ratios from the balanced equation to find the theoretical yield of HCl. This calculation is not provided in the question and would require additional information such as the molar mass of PCl3 and HCl. But to find the percent yield, you would take the actual yield (91.0 g of HCl) divided by the theoretical yield and multiply by 100%.