Limiting Reactants

What is a Limiting Reactant? A limiting reactant is: the reactant that gets used up the reactant that stops the reaction the reactant that limits the amount of product that can form

Example Is this equation balanced?

Example How many S’mores CAN be made from the ingredients shown? Which ingredient limits the number of S’mores that can be made?

Affect of the Limiting Reactant All of the chocolate will be used up making 2 S’mores, but there will be 3 marshmallows and 1 graham cracker left over. They are in excess.

Learning Check Which is the limiting reactant in the following equation?

Calculating the Limiting Reactant We must compare the actual number of moles of each reactant to the balanced equation for the reaction. The reactant which will cause the smallest amount of product to form is the limiting reactant.

Calculating the Limiting Reactant 2H2 + O2 2H2O If we begin with 1.0 mole of H2 and 1.0 mole of O2, which will be the limiting reactant?

Calculating Limiting Reactant 1.0 mole H2 x = 1.0 mole H2O = expected yield 1.0 mole O2 x = 2.0 mole H2O

Calculating the Limiting Reactant H2O is the limiting reactant, since it will only allow 1.0 mole of H2 to be formed.

More About Limiting Reactant Calculations We can calculate limiting reactants from the reactant masses using the mass-to- moles calculation. This makes the procedure a multi-step procedure, but does not require any new calculations.