Balancing Equations
Balancing, Writing, and Naming
Equations
Balancing Equations
Balancing Equations

Law of Conservation of
Matter:



In a chemical reaction,
matter can be neither
created nor destroyed.
In a chemical reaction,
the amount of reactants
equal the amount of
products.
**Chemical Properties

Balloons can be filled with hydrogen gas (H2)
or helium gas (He) to make them rise. Helium
gas is safer to use than hydrogen because
hydrogen gas can burn in oxygen.
Corrosion





Corrosion is a chemical property.
Corrosion is the process by which a material is broken down
into new substances by reacting with substances in its
environment.
Example a rusting nail at the end of the nail, the metal is
being broken down into a new substance, rust. Rust has a
different physical property from the original metal.
It is a different color, and it cannot conduct electricity the way
the original metal could.
A chemical property of the original metal is that it can be
corroded by air.
Chemical Properties of Rust
Fe
Fe
0
2
+
Fe
Fe
Iron
+
=
0
0
2
2
Oxygen
Fe203
=
Fe203
Rust
Corrosion



Not all metal can be corroded by air.
The Statue of Liberty has reacted with the rainwater
and air over time to go from a shiny copper color to
a dull green color. It is made of copper, which will
corrode in air.
* A chemical property of copper is that is reacts with
air to form green copper sulfate.
Corrosion

Gold is a metal that will not corrode in air.
Some metals tarnish, or turn black when
exposed to air. Corroding and tarnishing are
chemical properties related to interactions
with air.
* Properties



Gold (Au)
Iron (Fe)
The property of gold makes it different from
iron it is because it does not rust.
Compounds and Formulas

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

Compounds- elements can combine in different ways
to form compounds. A compound is a type of matter
that forms when two or more elements combine
chemically.
Unlike a mixture, the substances that join together to
form a compound do not retain their individual
properties.
Example: Table salt is a compound that forms when
sodium and chlorine combine chemically. Sodium is
a metal that explodes when combined with water.
Chlorine is a poisonous gas.
However, when these elements combine together to
form sodium chloride, they form the edible, white
solid you know as table salt.
Chemical Formula




When elements combine to form compounds, they combine
in specific ratios.
Example: When sodium and chlorine atoms combine to make
salt, they combine in a 1:1 ratio. There is one sodium atom
for every chlorine atom in table salt.
Every compound that is formed has a name and a chemical
formula. The chemical formula of a compound tells you what
elements have combined to make that compound and in what
ratio they have combined.
Example: water is a compound that is made up of hydrogen
and oxygen atoms. When they combine chemically to make
water, they combine in a 2:1 ratio of hydrogen to oxygen.
Two hydrogen atoms combine with every one oxygen atom.
A Water Molecule

O
H
H
Water H2O
A water molecule has
the formula H2O. This
formula tells you that
the molecule has 2
hydrogen atoms and 1
oxygen atom.
*Subscript
O
H


H


Water H2O

The chemical formula of water
H20, gives you this information. H
is the chemical symbol for
hydrogen, and the little number
after the H is called the Subscript.
*A subscript tells us how many
atoms of that element are found in
one molecule of a compound.
For water, two hydrogen atoms
are needed in each molecule, or
unit, of water.
0 is the chemical symbol for
oxygen. When there is no number
it is understood that the subscript
is simply 1. So there is only one
atom of oxygen in the ratio.
One atom of oxygen combines
with two atoms of hydrogen to
make water. With the ratios of
atoms are changed, the compound
they produce changes.
Subscript Cont.

Hydrogen peroxide
H202
H
O
O
H

Hydrogen peroxide
contains the same elements
as water but in different
ratios which form different
molecules. Drinking water
is essential for your
survival, but hydrogen
peroxide is poisonous if
swallowed. The ratio of the
elements in a compound is
just as important as the
identity of the elements in
that compound in
determining its physical
and chemical properties.
Chemical Formulas

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
Carbon dioxide is a gas found in the air. Its chemical
formula is C02. How many different elements are in
this formula?
The answer is two carbon and oxygen.
How many atoms of each element does it have? To
answer his question, we look at the subscripts.
Remember if there is no number after the element, it
is understood to be 1.
So there is 2 subscripts those are two oxygen atoms.
How many total atoms are in one molecule of CO2?
There are a total of three atoms: one carbon atom
and two oxygen atoms.
Atoms


How many atoms make up one molecule of
methane?
5
Other Chemical Formulas
A. Balancing Steps
1. Write the unbalanced equation.
2. Count atoms on each side.
3. Add coefficients to make #s equal.
Coefficient  subscript = # of atoms
4. Reduce coefficients to lowest
possible ratio, if necessary.
5. Double check atom balance!!!
B. Helpful Tips




Balance one element at a time.
Update ALL atom counts after adding a
coefficient.
If an element appears more than once per
side, balance it last.
Balance polyatomic ions as single units.

“1 SO4” instead of “1 S” and “4 O”
Why is there a 2 after the oxygen?
__________________
Oxygen is diatomic
What are all the diatomic elements?
Br, I, N, Cl, H, O, F
_________________
4
1
12
2
10
4
2
8
Yields
Reactants
Subscript
Products
Coefficient
*Examples


*The chemical formula for sodium nitrate is NaNO3.
It is used in explosives and also as a preservative in
some foods. The elements that make up sodium
nitrate is: sodium, nitrogen, and oxygen.
*How many total atoms are in one molecule of
sodium nitrate? NaNO3



5
*Ammonium perchlorate is used in rocket fuels. How many
atoms are in the chemical formula for ammonium perchlorate,
NH4CIO4?
1
Balancing Equations


Paraphrase:
Law of Conservation of
Atoms:

The number of atoms of
each type of element must
be the same on each side
of the equation.
Balancing Equations
 Hydrogen
 H2



+ oxygen
+ O2
water
H2O
Hydrogen and oxygen are diatomic elements.
Their subscripts cannot be changed.
The subscripts on water cannot be changed.
Balancing Equation

Count the atoms on each side.


Reactant side: 2 atoms H and 2 atoms
O
Product side: 2 atoms H and 1 atom O
 H2
+ O2
H2O
Balancing Equations

H2 + O 2
H2O

If the subscripts cannot be altered, how can
the atoms be made equal?

Adjust the number of molecules by changing
the coefficients.
Balancing Equations



Reactants: 2 atoms of H and 2 atoms of
O
Products: 4 atoms of H and 2 atoms of
O
H is no longer balanced!
 H2
+ O2
2H2O
Balancing Equations
 2H2



+ O2
2H2O
Reactant side: 4 atoms of H and 2 atoms of O
Product side: 4 atoms of H and 2 atoms of O
It’s Balanced!
Balancing Equations
 N2


+ H2
Nitrogen + hydrogen
NH3
ammonia
Count atoms.


Reactants: 2 atoms N and 2 atoms H
Products: 1 atom N and 3 atoms of NH3
Balancing Equations


Nothing is balanced.
Balance the nitrogen first by placing a
coefficient of 2 in front of the NH3.
 N2
+ H2
2NH3
Balancing Equations




Hydrogen is not balanced.
Place a 3 in front of H2.
Reactant side: 2 atoms N, 6 atoms H
Product side: 2 atoms N, 6 atoms H
 N2
+ 3H2
2NH3
Balancing Equations
 Ca3(PO4)2
+ H2SO4
+ H3PO4
CaSO4

Count atoms in the product.

Ca atoms – 1, S atom – 1, O atoms – 4; H
atoms – 3, P atom – 1, O atoms - 4
Balancing Equations

A coefficient of 2 placed in front of
H3PO4 which balances both hydrogen
and phosphate.
 Ca3(PO4)2
+ 3H2SO4
3CaSO4 + 2H3PO4
Balancing Equations

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Cu + H2SO4
CuSO4 + H2O + SO2
The sulfate group breaks up. Each atom must
be counted individually. Ugh!
Reactants: Cu – 1, H – 2, S – 1, O – 4
Products: Cu – 1, S – 1, O - 4, H – 2, O – 1, S
– 1, O - 2
Balancing Equations


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Sulfur is not balanced.
Place a two in front of sulfuric acid.
Count atoms: 2 H2SO4 H – 4, S – 2, O
-8
Cu + 2H2SO4
CuSO4 + H2O + SO2


Balancing Equations


Hydrogen needs to be balanced so place
a 2 in front of the H2O.
Count the number of atoms.
Cu + 2H2SO4
CuSO4 + 2H2O + SO2


Balancing Equations


Reactants: Cu – 1, H – 4, S – 2, O – 8
Products: Cu – 1, S – 1, O – 4, H – 4, O – 2,
S – 1, O – 2 = Cu – 1, S – 2, H – 4, O – 8
 It’s balanced!
Cu + 2H2SO4
CuSO4 + 2H2O + SO2


Balancing Equations

Balancing hints:


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Balance the metals first.
Balance the ion groups next.
Balance the other atoms.
Save the non ion group oxygen and
hydrogen until the end.
Balancing Equations



This method of
balancing
equations is the
inspection
method.
The method is
trial and error.
Practice.
Writing and Naming



Nickel + hydrochloric acid
Nickel(II) chloride + hydrogen
Write the corresponding formula
equation and then balance the equation.
Writing and Naming



Write each formula independently.
Ignore the rest of the equation.
Balance the equation after writing the
formulas.
Ni + HCl
NiCl2 + H2
Ni + 2HCl
NiCl2 + H2


Writing and Naming

Remember the diatomic elements: H2, N2, O2,
F2, Cl2, Br2, and I2.
Writing and Naming
Cu + H2SO4
 CuSO4 + H2O + SO2



Balance the formula equation.
Write the word equation.
Writing and Naming
Cu + 2H2SO4
CuSO4 + 2H2O + SO2

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

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Write the names:
Cu by itself is just copper. Copper(I) or
copper(II) would be incorrect.
H2SO4 should be named as an acid.
Sulfuric acid
States of Matter


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
(g) – Gas
(l) – Liquid
(s) – Solid
(cr) Crystal
(aq) – Aqueous (water solution)
Counting Atoms
1)
H3PO4
2)
3NaOH
3)
2K2C2H3O2
4)
Mg3(PO4)2
More Counting Atoms
1)
3Al(NO3)3
2)
3Al2(SO4)3
3)
2Ca(OH)2
4)
3NH4NO3
Balanced or not?
+
O2 

H2

CH4 +

Mg + O2
O2
H2O
 CO2 + H2O
 MgO
Cellular respiration can be described
by the following chemical equation:



C6H12O6 + 6 O2
glucose
oxygen
6CO2 + 6H20 + ENERGY
carbon dioxide
water
(ATP)
Respiration Clip

Photosynthesis can be described

6 CO2 + 6 H20
by the following chemical equation:
C6H12O6 + 6 O2
Photosynthesis Clip
Balancing Equations

Practice problems on board