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Reaction Notes Part II
How to balance a chemical equation
Why do we need to balance a chemical
equation?

Sometimes, a written equation DOES NOT have equal
number of reactants and products.

Example:
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Key Thought: A balanced chemical equation gives scientists
information about the relative ratio between the number
of reactants and the number of products.
How to “balance” a chemical equation
• To balance a chemical equation, chemists use
COEFFICIENTS.
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• Example:
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The “Easy” Method of Balancing
• The acronym MINOH makes balancing chemical reactions a little easier.
Title
Examples
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• The acronym CHO makes combustion reactions much easier to balance.
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The Process of Balancing I
Step 1:
Step 2:
• Na + Cl2
→
NaCl
NOTICE: When the number of products and reactants
do not equal the equation must be unbalanced.
The Process of Balancing II
Step 3: Apply the coefficient to the equation
Step 4: Distribute the coefficient to each atom.
Step 5: Check to see if the products and reactants equal
• Na + Cl2
→
NaCl
Balancing Example #2
• Fe
+
O2
→
Fe3O2
NOTICE: Subscripts indicate how many are present to
the LEFT.
Balancing Example #2
• 3Fe
+
O2
REACTANT SIDE
Fe : 1 x 3 = 3
→
Fe3O2
PRODUCT SIDE
Fe : 3 x 1 = 3
NOTICE: Now Fe and O2 have the same number of
atoms when they react to form Fe3O2.
Balancing Example #3
• C4H8 + O2
REACTANT SIDE
→
CO2+ H2O
PRODUCT SIDE
NOTICE: On the PRODUCT side, O is present in BOTH
products.
Balancing Example #3
• C4H8 + 6O2
REACTANT SIDE
→
4CO2+ 4H2O
PRODUCT SIDE
NOTICE: This equation satisfies the Law of
Conservation of Mass by using coefficients.
Balancing Example #4
• Ag2S + KCN →
REACTANT SIDE
KAg(CN)2+ K2S
PRODUCT SIDE
K :1
+
2
NOTICE: All atoms have the same numbers in both
Products and Reactants.
Balancing Example #5
• Hg(OH)2 + H3PO4 → Hg3(PO4)2+ HOH
REACTANT SIDE
Hg: 1
OH: 2
H: 3
PO4: 1
PRODUCT SIDE
NOTICE: All atoms have the same numbers in both
Products and Reactants.
Balancing Example #6
• I2 + HNO3 →
I:
H:
NO3:
HIO3 + NO2 + H2
IO3:
H:
N:
O:
NOTICE: All atoms have the same numbers in both
Products and Reactants.
Balancing Example #7
• C4H10 + Cl2 + O2 →
C:
H:
Cl:
O:
CO2 + CCl4 + H2O
C:
H:
Cl:
O:
NOTICE: All atoms have the same numbers in both
Products and Reactants.
In-Class/Homework Assignment
– Homework:
• Worksheet: Balancing Chemical Equations, 1-25

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