Final answer:
The theoretical yield is calculated using the balanced chemical equation and molar masses of reactants and products which is then compared with the actual yield to determine the percent yield.
Step-by-step explanation:
The theoretical yield of a chemical reaction is the maximum amount of product that can be produced from a given amount of reactants under ideal conditions, based on stoichiometry. To calculate the theoretical yield, one must first use the balanced equation to determine the mole-to-mole ratios between reactants and products. Then, using the molar masses of the reactants and products involved, you can convert grams of reactants to moles, apply the stoichiometric ratios, and finally convert back to grams to find the theoretical mass of the products expected.
For example, consider the synthesis of aspirin from salicylic acid (C7H6O3) and acetic anhydride (C4H6O3) which forms aspirin (C9H8O4) and acetic acid (HC2H3O2). If you start with 12.66 g of salicylic acid, converting this mass to moles and using the mole ratio from the balanced equation allows you to calculate the theoretical yield of aspirin. The actual yield is the quantity of product obtained from the reaction. The percent yield is then calculated by dividing the actual yield by the theoretical yield and multiplying by 100%.
In cases where a reaction doesn't go to completion, or there are losses during the process, the actual yield will be lesser than the theoretical yield, resulting in a percent yield of less than 100%.