From the two reactants that are to be used in a reaction, it can be determined what the limiting reactant will be. Using the mass of the limiting reactant -the theoretical yield can be determined.
The theoretical yield represents the mass of product that can be made if the reaction reaches 100% completion.
This will not happen, mostly due to thermodynamics, equilibrium, and impure reactants. Therefore the actual yield will be a little less than the theoretical yield.