Balancing Chemical Equations
What goes in must
come out!
Objectives
At the end of the lesson, the learners will be
able to:
1. carry an investigation to determine if mass is
conserved in chemical reactions;
2. mathematically proved that matter is
conserved in chemical reactions by
balancing chemical equations; and
3. write and balance chemical equation.
Balancing Chemical Equations

Balancing a chemical equation is much like
the work of an accountant who has to show
every penny that comes in and where it has
gone to.
Law of Conservation of Mass
You need to remember this law!


The Law of Conservation of Mass states:
that mass is neither created nor
destroyed in any chemical reaction.
Therefore balancing of equations requires
the same number of atoms on both sides of a
chemical reaction.
The number of atoms in the Reactants must
equal the Number of atoms in the Products
Law of Conservation of Mass

The mass of all the reactants (the
substances going into a reaction) must equal
the mass of the products (the substances
produced by the reaction).

Reactant + Reactant = Product
Chemical Equations
Because of the principle of the
Conservation of Matter,
an equation
must be
balanced.
It must have the same
number of atoms of the
same kind on both sides.
Lavoisier, 1788
REACTANTS
PRODUCT
Reactants
- the starting materials, substances that
changes when it is combined with another
substance in a chemical reaction
Product
- the new substance. The substance that
result of a chemical reaction.
Other components of an equation
Coefficient
- is the number before a symbol or
formula of a substance
Subscript
- is the number of atoms of the element
found below the substance.
Steps in Balancing an Chemical Equation
1. Count atoms of
each element on the
two side of the
equation.
2. Determine which
atoms needs to be
balance .
3. Balance element one at
a time by placing the
correct coefficient in
front of the chemical
formula.
Note that you can
CHANGE the
coefficient BUT NOT
the subscript.
Steps to Balancing a Chemical Equation
4. Multiply the coefficient
of each element by
the subscript of the
element to count the
atoms. Then list the
number of atoms of
each element on each
side.
5. Recheck the number of
atoms in the two sides
of the equation.
Repeat if there are
discrepancies in the
result.
BALANCE CHEMICAL EQUATION
are those whose coefficients result in equal
numbers of atoms for each element in the
reactants and products.
Balancing Chemical Equations
An easier way
First you need an equation with the correct “formulae”
………. You’ll probably be given this in the question
Just like this one
Mg + O2  MgO
Then all you do is list the atoms that are involved
on each side of the arrow
Mg + O2  MgO
Mg
O
Mg
O
Then start balancing:
[1] Just count up the atoms on each side
Mg + O2 
MgO
1
Mg
1
2
O
1
[2] The numbers aren’t balanced so then add “BIG”
numbers to make up for any shortages
Mg + O2  2 MgO
And adjust totals
1
Mg
1
2
2
O
1
2
But the numbers still aren’t equal, so add
another “BIG” number
2 Mg + O2  2 MgO
2
1
Mg
2
2
O
2
And adjust totals again
NOW BOTH SIDES HAVE EQUAL
NUMBERS OF ATOMS
WE SAY THAT THE
EQUATION IS BALANCED!!
LETS
PRACTICE !
NH2 + O2
NO + H2O
BaSO4 + NaCl
Na2SO4 + BaCl2
CaCO3 + H3PO4
Ca3(PO4 ) 2 + CO2 + H2 O
2. Al + HCl
AlCl3 + H2
3. (NH4)2 Cr2O7
Cr2 O3 + N2 +H2O
4. CaCO3 + H3 PO4
Ca3 (PO4 )2 + CO2 + H2O
5. NaClO3
NaCl +O2
Mole Relationship in a
Chemical Reaction
Objective
At the end of the lesson, you should be able to:
to define a mole and molar mass
2) determine the molar mass of elements and
compounds
3) determine whether your results support the
Law of Conservation of Matter
1)
MOLE RELATIONSHIP IN
CHEMICAL EQUATION
In all the chemical reactions that you
studied, you balance all the equations in terms
of number of atoms and molecules in the
reaction.
The coefficients in the balanced equation give
the ratio of moles of reactants and products
What is a Mole/ mol ?
A mole (symbol, mol)is defined as the amount
of a substance containing the same number of
representative particles like atoms, molecules,
ions or formula units.
The mole is the SI (International System) unit
for amount of substance.
Mole/ mol
a mole of a substance contains
6.022141 x 1023 representative
particles.
The number 6.02 x1023 is called
Avogadro’s Number, in honor of
Amadeo Avogadro.
What is Molar mass?
Molar mass is defined as the mass in grams of 1
mole of atoms or molecules of a substance.
For instance, one mole of Carbon atoms has 1
molar mass of C is equal to 12 grams (or amu).
Molecular Mass
Molecular mass (also known as molecular weight) is the
sum of the atomic mass of each atom in a molecule,
multiplied by the number of atoms of that element in
the molecule.
Example; Water (H2O)
Element
H
O
No. of Atom
2
1
Atomic mass
X 1.0
= 2.0 g
X 16.0 = 16.0 g
molar mass =18.0 g/mol
Example # 2
Find the molar mass of glucose (C6H12O6)
ELEMENT
C
H
O
NO. OF ATOMS
6
12
6
ATOMIC
MASS
X 12.0 g = 72.0 g
X
1.0 g = 12.0 g
X 16.0 g = 96.0 g
molar mass: 180.0 g/mol
thus, a mole of glucose weighs 180.0 grams
Example # 3
Find the molar mass of Ca(PO4)2
ELEMENT
NO. OF ATOMS
ATOMIC MASS
Ca
P
O
1
x 40.0 g = 40.0 g
1 (2) = 2
x 31.0 g = 62.0 g
4 (2) = 8
x 16.0 g = 128.0 g
molar mass : 230.0 g/mol
Calculate Molar mass
Ex.
4NH3 + 5O2
4NO + 6H2O
Calculate Molar mass
2 Li + 2 HNO3  2 LiNO3 + H2
1. Fe (OH)3 + H2 SO4
Fe2 (SO4 ) 3 + H2O
Balancing Practice
 For more help go to:
http://richardbowles.tripod.com/chemistry/bal
ance.htm#part0
 For some fun balancing equations go to:
 http://www.mpcfaculty.net/mark_bishop/bala
ncing_equations_tutorial.htm
THANK YOU!
Try to balance these equations and calculate the
molar mass.
[1] Na + Cl2  NaCl
[2] CH4 + O2  CO2 + H2O
[3] Li + HNO3  LiNO3 + H2
[4] Al + O2  Al2O3