1. High School Chemistry - Core Concept Cheat Sheet
11: Balancing Equations
Key Chemistry Terms
Example #1
 Law of Conservation of Mass/Matter: Matter cannot be
created nor destroyed in a chemical reaction.
Convervation of Mass Mnemonic: In balancing an
equation, the number of atoms of each element in the
reactant side must be equal to the number of atoms of each
element in the product side = “What goes in must come out!”
Chemical Equations
 Reactants  Products
 Subscripts balance charges in a compound and indicate
number of atoms in a compound.
 The Law of Conservation of Mass/Matter requires that a
chemical reaction be balanced.
 Coefficients balance atoms in a chemical reaction and
indicate the number of compounds in a reaction.
+
2+
Zn + H  Zn
Zn
H
Charge
+ H2
Reactants
1
1
+1
__ Zn + _2_ H+  __ Zn2+ + __ H2
Reactants
Zn
1
H
1 2
Charge
+1 2
H2 & O2 are reactants; H2O is a product.
2 moles of H2 react with 1 mole of O2 and produces 2
moles of H2O.
Choosing Which Element to Begin With
 Start with:
o Elements that appear only one time on each side.
o Elements in the most complex compounds.
Products
1
2
+2
1 Zn + 2 H+  1 Zn2+ + 1 H2
Example #2
NaOH + MgCl2  NaCl + Mg(OH)2
Reactants
Na
1
OH
1
Mg
1
Cl
2
Example:
2 H2 (g) + O2 (g)  2 H2O (l)
Products
1
2
+2
Products
1
2
1
1
_2_ NaOH + __ MgCl2  __ NaCl + __ Mg(OH)2
Reactants
Products
Na
1 2
1
OH
1 2
2
Mg
1
1
Cl
2
1
_2_ NaOH + __ MgCl2  _2_ NaCl + __ Mg(OH)2
Reactants
Products
Na
1 2
1 2
OH
1 2
2
Mg
1
1
Cl
2
1 2
 Save for the end:
o Elements that appear more than once on a side.
o Elements that are uncombined on a side.
Examples:
C3H8 + O2  CO2 + H2O
2 NaOH + 1 MgCl2  2 NaCl + 1 Mg(OH)2
Save oxygen for last—it appears more than once
on the products, and it appears uncombined on the
reactants.
Example #3
C3H8 + O2  CO2 + H2O
Inspection Method
Reactants
Method to balance the most simple reactions:
1.
Make a list of the elements in the reaction. You may
leave polyatomic ions together if they appear identically
on both sides of the reaction.
2.
Count the number of each type of atom on each side of
the reaction.
3.
Add coefficients to balance the number of atoms.
4.
Determine the total charge of each side of the reaction
and use coefficients to balance charge.
5.
When all elements and charge are balanced, place a “1”
in any empty coefficient location to indicate that you’re
done.
C
H
O
3
8
2
Products
1
2
3
__ C3H8 + __ O2  _3_ CO2 + __ H2O
Reactants
C
H
O
3
8
2
1
2
3
Products
3
7
__ C3H8 + __ O2  _3_ CO2 + _4_ H2O
Reactants
C
H
O
3
8
2
Products
1 3
2 8
3 10
Inspection Tip: The key is to pick the first element which
should be the one that appears only once per side. If you
still have difficulty, use the MINOH Sequence, which works
well for most. Follow this order: Metal - Ion (polyatomic) –
1 C3H8 + 5 O2  3 CO2 + 4 H2O
Nonmetal – Oxygen - Hydrogen = “MINOH”.
How to Use This Cheat Sheet: These are the keys related to this topic. Try to read through it carefully twice then recite it out on a
blank sheet of paper. Review it again before the exams.
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