How can I find the percentage yield?
Percent yield represents the ratio between what is experimentally obtained and what is theoretically calculated, multiplied by 100%.
So, let's say you want to do an experiment in the lab. You want to measure how much water is produced when 12.0 g of glucose (
Since you have a
This represents your theoretical yield. If the percent yield is 100%, the actual yield will be equal to the theoretical yield. However, after you do the experiment you discover that only 6.50 g of water were produced.
Since less than what was calculated was actually produced, it means that the reaction's percent yield must be smaller than 100%. This is confirmed by
You can backtrack from here and find out how much glucose reacted
So not all the glucose reacted, which means that oxygen was not sufficient for the reaction - it acted as a limiting reagent.
As a conclusion, percent yield problems always have one reactant act as a limiting reagent, thus causing a difference between what is calculated and what is actually obtained. A percent yield that exceeds 100% is never possible, under any circumstances, and means that errors were made in the calculations.