Percent Yield
Percent Yield
 “yield—” the amount of product actually made through a
chemical reaction. Why is this value important?
 Theoretical yield— calculated amount of product
 Actual/Experimental yield– the “true/actual” amount of
product made in the chemical reaction, usually less than
theoretical
 How is this value different than percent error?
Percent Yield
 = Actual yield
x 100%
Theoretical yield
Ex. 98.80% of Mg3N2 was produced in a chemical
reaction. What happened to the rest? (purity, other
reactions, remaining product, etc.)
Limiting Reactant
Stoichiometry Refresher
 ____ Mg + _____ Cl2  MgCl2
10.0 grams of magnesium metal reacts with chlorine. How
many grams of magnesium chloride are produced?
Limiting Reactant
 Chemical compound that “limits” or determines how
much product can be produced
 All of the compound is consumed in the reaction
 Excess reactant—
 chemical compound not consumed in the reaction
 plenty of the compound is available for the chemical
reaction
Steps to find the limiting
reactant
 Two stoichiometry problems in ONE ! 
1) Write a balanced equation
2) Find the amount of product (in grams) produced from
each reactant amount.
3) The reactant producing the SMALLEST product is the
limiting reactant.
Example 1
_____ Mg + ______ O2 
MgO
10.0 grams of magnesium metal reacts with 10.0 grams of
oxygen. What is the mass of magnesium oxide produced
in this reaction?
What is the limiting reactant?
Example 2
Aspirin synthesis:
2C7H6O3 + C4H6O3
2C9H8O4 + H2O
When 20.0g of C7H6O3 and 20.0g of C4H6O3 react, which
is the limiting reactant? What is the mass (in grams) of
aspirin produced?
What is the limiting reactant?
Example 3
 _____ I2O5 + _____ CO  _____ CO2 + ____ I2
80.0 grams of I2O5 reacts with 28.0 grams of CO. What is
the mass of I2 that can be produced from this reaction?
What is the limiting reagent?
Example 4
 __C3H6 + ___NO  __C3H3N + ____H2O + ____ N2
If I have 21.6 grams of C3H6 and 21.6 grams of NO, how
much (in grams) C3H3N will I produce?
What is the limiting reagent?
Homework
 p. 464 #2-3