Percent yield is a chemistry term for the percent of a substance produced in a reaction as compared to how much should have been produced in a complete reaction. A scientific or graphing calculator is needed to balance the terms and then calculate the percentage.
Balance the equation
When creating a chemical reaction, you should write an equation that expresses the ratios of substances that are combined which balances with the amount of each element in the substances produced. Each substance is massed in grams before being added to the chemical reaction. Using the mass of those substances, account for the number of moles of each starting material. Use the ratios to determine which substances should be completely used and which ones should be left over. Assuming all of the available starting elements recombine in the reaction, calculate how many moles of the newly created substance would be present as a result of the reaction. Once that equation is set up and all units are attached to constants, that equation is considered balanced.
Find the theoretical yield
Take the number of moles of substance produced, according to your equation. Convert that number of moles into mass in grams. This is the theoretical yield of the substance.
Divide the actual by the theoretical
Mass the amount of the substance actually produced in the reaction. Divide the actual yield by the theoretical yield. Multiply by 100. This number is the percent yield.