(2.3) Balancing Chemical
Equations
(p150)
Conservation of Mass



As we saw in class, the mass of the
reactants must equal the mass of the
products in a chemical reaction.
To show that a reaction is balanced, we
must write a balanced chemical equation.
In a balanced chemical equation, the
number of atoms on each side of the
equation is the same.
How To Write a Balanced
Chemical Equation
1. The chemical formula for a substance
CANNOT be changed!
ex. CO2 molecules must stay as CO2
How To Write a Balanced
Chemical Equation
2. From the word equation, write the
chemical equation using the correct
chemical formula for all the substances
involved.
ex. The combustion of ethanol (C2H6OH)
ethanol+ oxygen  carbon dioxide + water
C2H6OH +
O2 
CO2 +
H2O
How To Write a Balanced
Chemical Equation
3. Count the number of atoms in both the
reactants and products.
4. Multiply each formula by a coefficient
to balance the number of each kind of
atom in both the reactants and
products.
THE RAP SHEET


The RAP sheet is a methodology used
to help balance chemical equations.
It helps keep track of the number and
kinds of atoms in a chemical equation.
C2H5OH + O2  CO2 + H2O
Add coefficient 2 CO2
Add coefficient 3 to H2O
Add coefficient 3 to O2
R
A
P
Reactants
Atoms
Products
7
2
C
1
6
H
2
3
O
3
2
6
5
7
TRY THESE

Worksheets 2.3 (D) and 2.3 (E)
(2.3) Balancing Chemical
Equations
(p150)
ASSIGNMENTS:

Workbook p56
p60-63