Actual yield is defined as the amount of a specified substance produced at the end of a chemical reaction performed in actuality, rather than theoretically. Actual yield is very often lower than the amount of substance predicted by chemical equations.
Theoretical yield is the amount of product predicted to form from a chemical reaction, based simply upon pure mathematical abstractions. Theoretical yield is an idealization. Under real-world conditions, reactions may create less product due to impurities, competing chemical reactions or less than ideal conditions. Actual yield is the amount that is actually produced by a technique or experiment.
Actual yield and theoretical yield are used to find the percent yield, a measure of how much product was produced as compared to how much could have been produced ideally. A percent yield of 100 percent means that the reaction ran to completion and produced the exact amount of substance predicted by chemical equations.