Stoichiometry
Introduction
Introduction to Stoichiometry
Stoichiometry – study of the mass relationships
between reactants and products in a chemical
reaction.
Mg(s) + 2 HCl(aq) → MgCl2 (aq) + H2 (g)
Mole Ratio
2 Al2O3(l) → 4 Al(s) + 3 O2 (g)
2 m ol Al2O3
4 m ol Al
or
4 m ol Al
2 m ol Al2O3
2 m ol Al2O3
3 m olO2
or
3 m olO2
2 m ol Al2O3
4 m ol Al 3 m ol O2
or
3 m ol O2
4 m ol Al
Mole Ratio
How many moles of Aluminum can be
produced from 13.0 moles of aluminum
oxide?
 4 m ol Al 
  26.0 m ol Al
13.0 m ol Al2O3  
 2 m ol Al2O3 
Practice
2 Al2O3(l) → 4 Al(s) + 3 O2 (g)
1. If 26.0 moles of aluminum are produced in a
reaction, how many moles of oxygen will also
be produced?
2. How many moles of aluminum oxide are
required to produce 18.1 moles of aluminum?
3. If 23.0 moles of aluminum oxide react, how
many grams of Aluminum will be produced?
Limiting Reactants
Objective:
1. Identify the limiting reactant in a chemical reaction
2. Use the limiting reactant to calculate the maximum
amount of product formed or the excess reactant in a
reaction.
Limiting Reactant – reactant that limits the amount of
products that can form in a chemical reaction.
Excess Reactant – substance that is not completely used
up in a reaction
Limiting Reactants
N2 + 3 H2  2 NH3
Which is the limiting reactant?
Finding the Limiting Reactant
N2H4 (l) + 2 H2O2 (l)  N2 (g) + 4 H2O(l)
Which is the limiting reactant when 0.750 mol of N2H4
is mixed with 0.500 mol of H2O2?
• A given amount of a reactant is used to determine the
required amount of the other reactant. That amount is
then compared to the actual amount.
 2 m olH 2O2 
  1.50 m olH 2O2
0.750m olN 2 H 4  
 1 m ol N 2 H 4 
Finding the Limiting Reactant
N2H4 (l) + 2 H2O2 (l)  N2 (g) + 4 H2O(l)
How much of the excess reactant, in moles
remains unchanged?
 1 m ol N 2 H 4 
  0.250m ol N 2 H 4
0.500m olH 2O2  
 2 m olH 2O2 
0.750molN 2 H 4  0.250molN 2 H 4  0.500molN 2 H 4
How much of each product forms?
0.250 mol N2 & 1.00 mol H2O
Amount of product in a Limiting Reactant Problem
What mass of barium nitride is produced from the
reaction between 22.6 g barium and 4.2 g
nitrogen gas?
Percent Yield
actual yield
percent yield 
 100%
theoretical yield
Theoretical yield – maximum amount of product that
can be produced as determined by a stoichiometric
calculation and based on the law of conservation of
matter
Actual Yield-amount obtained in a reaction
Percent Yield
Methanol can be produced through the reaction of CO
and H2 in the presence of a catalyst. If 75.0 g of CO
reacts to produce 68.4 g CH3OH, what is the percent
yield?