BALANCING CHEMICAL
EQUATIONS
Chapter 6.5
DAY 1 & 2
 Word
equations or formula (skeleton)
equations need to be balanced.
 The
number of atoms of one element on
the reactant side of an equation must
equal the number of atoms of that same
element on the product side of an
equation.
LAW OF CONSERVATION OF MASS
 This
law states: the total mass of atoms
must be the same on both sides of an
equation.
 This
means that the mass of the reactants
equals the mass of the products.
 In
other words, atoms can be neither
created or destroyed in a chemical
change.
How to count atoms review
 Using
Black line 6.5a, we will review
counting atoms before we learn the skill of
balancing equations.
1) The symbol of an element represents one atom
of that element
Example: Ca = 1 atom
2) A subscript is a number written at the lower
right corner after the symbol of an element. If
there is more than one atom of the element in
the molecule, then a subscript is used to indicate
the number of atoms.
Example: N2 = 2 atoms
3) A subscript outside a bracket multiplies all
the elements inside the brackets.
Example: Ba3(PO4)2
Barium – 3 atoms
Phosphorus – 2 atoms
Oxygen – 8 atoms
4a) A coefficient is a number written in front of
a chemical symbol and indicates the number of
atoms of that element.
Example: 3C = 3 carbons
4b) A coefficient is a number written in front of
a chemical formula and indicates the number of
molecules of that compound.
2H2O = Hydrogen 2 x 2 = 4 atoms,
Oxygen 1 x 2 = 2 atoms
NOTE: A coefficient multiplies the number of
atoms of each element in the formula.
4Cu(NO3)2 =
Copper 1 x 4 = 4 atoms,
Nitrogen 1 x 2 x 4 = 8 atoms,
Oxygen 3 x 2 x 4 = 24 atoms
LET’S BALANCE EQUATIONS
STEP 1 – Write the formula equation of the
reaction.
Example: CH4 + O2
CO2 + H2O
STEP 2 – Count the number of atoms of
each type on the reactants side and on
the products side
reactants
O–2
C–1
H–4
products
O-3
C-1
H–2
Step 3 Multiply each of the formulas by an
appropriate coefficient to balance the numbers of
atoms.
CH4 + 2 O2
CO2 + 2 H2O
Step 4 Count atoms on each side to verify.
reactants
O–4
C–1
H–4
products
O-4
C-1
H–4
1)
hydrogen and oxygen produce water
H2 + O
H2O
PRACTICE

Aluminum and Oxygen produce Aluminum Oxide

Al + O2
Practice
Al2O3

Ethylene and Oxygen produces carbon dioxide and water

C2H4 + O2
Practice
CO2 + H20

Carbon dioxide and hydrogen produces Methane and water

CO2 + H2
Practice
CH4
+
H20
PAGE 229 # 2, 3ade
Practice worksheet
BLM 6.5c Assignment
Class Work