Limiting Reactants
Reactants  Products
• Limiting Reactant: Determines the
amount of products that can be made
• Excess Reactant : Left over reactants
Identifying the Limiting Reactant
• Convert each reactant to grams of a
product using stoichiometry
• The reactant that makes the least
amount of products is the limiting
reactant
Sample Problem
Which is the limiting reactant if
25.0 grams of phosphorus reacts
with 50.0 grams of oxygen?
P4 + 5O2  P4O10
P4 is limiting
Sample Problem
A 2.00 g sample of ammonia is mixed
with 4.00 g of oxygen. How much NO
is produced and which is the limiting
reactant?
4 NH3(g) + 5 O2(g)  4 NO(g) + 6 H2O(g)
Sample Problem
An alkaline battery produces energy
according to the following reaction.
Determine the limiting reactant if 25.0 g of
Zn and 30.0 g of MnO2 are used. What
mass of Zn(OH)2 is produced?
Zn + 2MnO2 + H2O  Zn(OH)2 + Mn2O3
MnO2 is limiting
Excess Reactants
• The amount of excess reactants
can be determined by using
stoichiometry to find the amount
of reactants that is needed to
react with the limiting reactant.
Yield
• The theoretical yield represents the maximum
amount of product that can be formed from
given amounts of reactants
• The actual yield is the amount of product that
actually forms when the reaction is carried out
(in the laboratory). It is considered as an
experimental value.
Percent Yield
A ratio of actual yield to
theoretical yield
Why might percent
yield be important?
Percent yield is important,
because…
• Higher yield=less waste
• Less waste= lower cost for products
Percent Error: how much
error there is between
actual and theoretical yield
Sample Problem
Aluminum hydroxide is often present in antacids
to neutralize stomach acid (HCl). If 14.0 g of
aluminum hydroxide is present in an antacid
tablet, determine the theoretical yield of
aluminum chloride produced when the tablet
reacts with stomach acid. If the actual yield of
aluminum chloride is 22 g, what is the percent
yield?
Al(OH)3 + 3HCl  AlCl3 + 3H2O
Al(OH)3 + 3HCl  AlCl3 + 3H2O
What is the percent error?