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Ch 9 Stoichiometry
Using Chemical Equations
Ch 9 Stoichiometry
Using Chemical Equations
1984, Union
Carbide Plant –
10000+ killed in
Bhopal, India
by Methyl
Isocyanate
1988 Pepcon,
Henderson Rocket
Fuel Explosion
Ch 9 Stoichiometry
Using Chemical Equations
Objectives
1. To understand more of the information given in a
balanced equation
2. To use a balanced equation to determine relationships
between moles of reactant and products
Ch 9 Stoichiometry
Using Chemical Equations
A. Information Given by Chemical Equations
• A balanced chemical equation gives relative numbers of
reactant and product molecules (or moles) that participate
in a chemical reaction.
• The coefficients of a balanced equation give the relative
numbers of molecules (or moles).
CO(g) + 2H2(g)
CH3OH(l)
How many moles of CH3OH will be produced from 1, 2, or
5 moles of CO?
How many moles of hydrogen will react with 1, 2, or 5
moles of CO?
Ch 9 Stoichiometry
Using Chemical Equations
B. Mole-Mole Relationships in a BALANCED Reaction
• A balanced equation can predict the moles of product
that a given number of moles of reactants will yield.
What number of moles of O2 will be produced by
the decomposition of 2, 1, or 5.8 moles of water?
Ch 9 Stoichiometry
Using Chemical Equations
B. Mole-Mole Relationships using Factor Analysis
• The mole ratio allows us to convert from moles of one
substance in a balanced equation to moles of a second
substance in the equation. Use dimensional/factor analysis
and mole ratios to calculate the answers below:
CH4(g) + 2O2(g)
CO2 + 2H2O(l)
4.2 moles of CH4 reacts with how many moles of O2?
4.2 moles of CH4 will produce how many moles of H2O?
Ch 9 Stoichiometry
Using Chemical Equations
Objectives
1. To learn to relate masses of reactants and products in a
chemical reaction
2. To perform mass calculations that involve scientific notation
Moles
Grams
Moles
Grams
Ch 9 Stoichiometry
Using Chemical Equations
A. Mass Calculations
If 9.0 grams of water are
decomposed to hydrogen and
oxygen, what mass of oxygen
gas is formed?
Ch 9 Stoichiometry
Using Chemical Equations
C. Mass Calculations: Comparing Two Reactions
• For equal masses of methane (CH4) and propane
(C3H8), which will use more oxygen when fully burned?
"Happy Mole Day to You" Chemistry Song
Ch 9 Stoichiometry
Using Chemical Equations
Double Bacon Cheeseburgers and Stoichiometry
• 1 Double Bacon Cheeseburger needs 1 bun, 2 patties, 2 slices of
cheese, 4 strips of bacon
• For 5 Double Bacon Cheeseburgers how many units of each
ingredient do I need?
• Fill in the final column below with how many complete burgers I can
make:
Buns
Patties
Cheese
Slices
Bacon
Strips
2
4
4
8
4
4
8
16
16
30
32
48
How Many
Burgers?
Ch 9 Stoichiometry
Using Chemical Equations
Objectives
1. To understand the concept of limiting reactants
2. To learn to recognize the limiting reactant in a reaction
3. To learn to use the limiting reactant to do stoichiometric
calculations
4. To learn to calculate percent yield
Ch 9 Stoichiometry
Using Chemical Equations
A. The Concept of Limiting Reactants
• Stoichiometric mixture
– N2(g) + 3H2(g)  2NH3(g)
Ch 9 Stoichiometry
Using Chemical Equations
A. The Concept of Limiting Reactants
• Limiting reactant mixture
– N2(g) + 3H2(g)  2NH3(g)
Ch 9 Stoichiometry
Using Chemical Equations
A. The Concept of Limiting Reactants
• For a Limiting reactant mixture the number of moles are
not balanced to match the reaction equation
– N2(g) + 3H2(g)  2NH3(g)
– Limiting reactant is the
reactant that runs out
first
– When the limiting
reactant is exhausted,
then the reaction stops
Limiting Reactants Game
Ch 9 Stoichiometry
Using Chemical Equations
B. Calculations Involving a Limiting Reactant
Ch 9 Stoichiometry
Using Chemical Equations
B. Calculations Involving a Limiting Reactant
Ch 9 Stoichiometry
Using Chemical Equations
C. Percent Yield
• Theoretical Yield
– The maximum amount of a given product that can be
formed when the limiting reactant is completely
consumed.
• The actual yield (amount produced) of a reaction is usually
less than the maximum expected (theoretical yield).
• Percent Yield
– The actual amount of a given product as the percentage
of the theoretical yield.
Ch 9 Stoichiometry
Using Chemical Equations
According to her pre-lab theoretical yield calculations a
student’s experiment should have produced 1.44g of
magnesium oxide. When she weighed her product after
reaction, only 1.23g of magnesium oxide was present.
What is the student’s percent yield?