This document defines key terms related to chemical reaction yields, including formula mass, stoichiometry, theoretical yield, actual yield, and percent yield. Formula mass refers to the total mass of an element or compound. Stoichiometry is the calculation of quantities in a chemical reaction. The theoretical yield is the amount of product calculated using stoichiometry, while the actual yield is the amount actually formed. Percent yield measures the efficiency of a reaction by comparing the actual and theoretical yields.