This Demonstration shows the effect of a limiting reagent during the formation of a product, given varying amounts of reactants. The two reactants, hydrogen and oxygen, are shown to yield the product, water, assuming an appropriate catalyst is present. The first set of cylinders shows the number of moles of each reagent, and the second set shows the final number of moles after the reaction has run to completion. Either of the reactants can be the limiting reagent, based on the initial number of moles and the stoichiometry of the reaction.