What is theoretical yield?

[2]H2 + O2 --> [2]H2O Theoretical Yield is how much of the product you should get from a chemical reaction. Not all of the reactants will actually react in a chemical reaction. If you have 5000 moles of Oxygen reacting with 2 mole of Hydrogen, obviously you would have some Oxygen leftover. The amount of remaining Oxygen is the excess reactant and the amount of H2O that should be formed (2 moles) is the theoretical yield.

[2]H2 + O2 --> [2]H2O Theoretical Yield is how much of the product you should get from a chemical reaction. Not all of the reactants will actually react in a chemical reaction. If you have 5000 moles of Oxygen reacting with 2 mole of Hydrogen, obviously you would have some Oxygen leftover. The amount of remaining Oxygen is the excess reactant and the amount of H2O that should be formed (2 moles) is the theoretical yield.

The amount of product that would have been seen if the reaction was able to go to completion and was perfect, no mistakes and completely pure products. You compare it to how much you found or saw in the experiment and then you can come up with a percentage that lets you know how accurate things were in the experiment.