Stoichiometry
Introduction
Introduction to Stoichiometry
Stoichiometry – study of the quantitative
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 mol Al2O3
4 mol Al
or
4 mol Al
2 mol Al2O3
2 mol Al2O3
3 mol O2
or
3 mol O2
2 mol Al2O3
4 mol Al 3 mol O2
or
3 mol O2
4 mol Al
Mole Ratio
How many moles of Aluminum can be
produced from 13.0 moles of aluminum
oxide?
 4 mol Al 
  26.0 mol Al
13.0 mol Al2O3  
 2 mol 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?
Class Warmup
Use the following reaction to answer the questions below.
Iron (II) oxide reacts with oxygen gas to produce iron (III)
oxide
1. How many moles of oxygen gas are required to react
with 2.4 moles of iron (II) oxide?
2. How many grams of iron (III) oxide will be produced
from 70.0 g of iron (II) oxide?
Class Warm-up
In a thermite reaction, powdered aluminum
reacts with iron (III) oxide to produce
aluminum oxide and molten iron. What mass
of aluminum oxide is produced when 2.3 g of
aluminum reacts with iron (III) oxide?
2 Al + Fe2O3  2 Fe + Al2O3
 1 mol Al  1 mol Al2 O3  101.9613 g Al2 O3 
  4.3 g Al2 O3


2.3 g Al 
 26.98154 g Al  2 mol Al  1 mol Al2 O3 
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?
For each of the following reactions and the given amount of
reactants, determine the limiting reactant.
Limiting Reactant
2 S + 3 O2  2 SO3
6 moles S
10 moles O2
______
2 Na + 2 H2O  2 NaOH + H2 4 moles Na
8 moles H2O
Mg2Si + 4 H2O  2 Mg(OH)2 + SiH4
______
1 mole Mg2Si ______
2 moles H2O
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 mol H 2O2 
  1.50 mol H 2O2
0.750 mol N 2 H 4  
 1mol N 2 H 4 
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?
Sample Problems
1. When 2.6 g of hydrogen react with 10.2 g of
oxygen, what mass of water will be produced?
2. If 4.1 g of chromium is heated with 9.3 g of
chlorine gas, what mass of chromium (III)
chloride will be produced?
3. What mass of sulfur dioxide is produced from
the reaction between 31.5 g of S8 and 8.65 g of
O2?
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 mol N 2 H 4 
  0.250 mol N 2 H 4
0.500 mol H 2O2  
 2 mol H 2O2 
0.750 mol N 2 H 4  0.250 mol N 2 H 4  0.500 mol N 2 H 4
How much of each product forms?
0.250 mol N2 & 1.00 mol H2O
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?
Review
10.45 g of aluminum reacts with 66.55 g of copper (II)
sulfate in a single replacement reaction.
a. What is the limiting reactant?
b. What is the mass of each product?
c. What is the mass of the excess reactant leftover at
the end of the reaction?