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Technical Science
Introduction to Chemistry
Chemical Equations slides 1-18
By John W. Pluemer
Chemical Equations
 In this tutorial you will…
– Analyze a Chemical Equation
– Prove a Chemical Equation is Balanced
– Explain Reasons for Balancing Equations
– Explore Common Chemical Reactions
Analyze a
Chemical Equation
1 of 5
Home
 One of the main functions of chemistry is to
determine what will happen when substances react.
 A chemical equation is the method used to express
what happens during a chemical reaction.
 The chemical equation below outlines a familiar
chemical reaction. What is this telling you?
2Na + Cl2  2NaCl
 A chemical equation is really just a recipe.
 It tells you the amounts of specific ingredients that
are required to make a certain amount of a product.
2 of 5
Analyze a
Chemical Equation
 Let’s take a closer look at that chemical equation.
2Na + Cl2  2NaCl
Reactants
Products
First,The
you
The“ingredients”
should
“results”
notice
on the
on
that
the
right
the
left
equation
side
side is
broken
of the
into
equation
two parts
arewith
called
anthe
arrow.
The arrow represents
Reactants
Products
the chemical reaction.
3 of 5
Analyze a
Chemical Equation
 Identify the reactants and the products in the
following reactions.
N2 + 3H2  2NH3
Reactants
Products
BaCO3  BaO + CO2
MnO2 + 4HCl  MnCl2 + Cl2 + 2H2O
4 of 5
Analyze a
Chemical Equation
 Let’s take another look at that chemical equation.
2Na + Cl2  2NaCl
Coefficients
Subscripts
The
Coefficients
The
Subscripts
coefficients
The
subscripts
small
tell
tell
numbers
in
the
in
the
this
this
number
number
equation
equation
following
of
ofatoms
atoms
tell
tell
us…
or
You
The
probably
large
numbers
noticed
in
the
front
numbers
of
theus…
molecules
Two
that
the
are
sodium
that
Na
chemical
bonded
is
are
in
atoms
required
elemental
together
symbols
will
for
react
form.
to
are
the
make
with
reaction.
associated
formulas
with
are
chemical
called
Coefficients.
formulas
for the
2 Cl atoms
Coefficients
One
are
a single
bonded
chlorine
called
molecule
to
molecule
Subscripts.
form
the
ofamounts
anot
aproducts.
molecule
substance.
towritten
produce
of the
of
chlorine gas.
(Coefficients
reactants
ofare
one
and
are
the
out.)
1 Na is bonded
(Subscripts
They
Two
tomolecules
determine
reactants
1 Cl of
to one
make
of
and
the
are
sodium
asubstance
products.
not
molecule
written
chloride.
itself.
ofout.)
sodium chloride.
Analyze a
Chemical Equation
5 of 5
Home
 What do the chemical equations below tell you?
N2 + 3H2  2NH3 (NH3 is Ammonia)
1 molecule of nitrogen gas reacts with 3 molecules of hydrogen
gas to form 2 molecules of ammonia. Nitrogen and hydrogen
molecules are each formed from 2 atoms bonded together.
Ammonia is formed from 1 N atom bonded to 3 H atoms.
2MgO + 4Si  2Mg + SiO2
2 molecules of Magnesium Oxide (each with 1Mg bonded to 1 O)
react with 4 atoms of silicon to form 2 atoms of magnesium
and 1 molecule of silicon dioxide (having 1 Si bonded to 2 O)
Prove a Chemical
Equation is Balanced
1 of 6
Home
Remember:tocoefficients
 An equation must be balanced
be useful.
of 1 are not written out.
 The equation below is not balanced. Can you see
what is missing?
2 Na + 1Cl2  2 NaCl
 There are no coefficients in the equation above.
 Coefficients determine the amounts of reactant and
product.
 The amounts of reactant and product are correct
when the coefficients make the equation balance.
2 of 6
Prove a Chemical
Equation is Balanced
 Prove the equation is balanced.
2Na + Cl2  2NaCl
Atom
Reactant
Product
Na
Cl
2
2
2
2
This
The
reaction
This
Coefficient
gives
is
abalanced
total
2all
and
of
two
because
the
lack
sodium
subscripts,
atoms
arehas
same
The
Remember,
We
First:
The
subscript
need
Second:
Third:
lack
Identify
to
of
akeep
balanced
aof
Count
Count
subscript
the
2of
track
and
the
the
the
chemical
of
ofnumber
and
number
types
lack
different
the
ofand
equation
of
coefficient
athere
ofcoefficient
atoms
numbers
atoms
elements
ofthe
of
on
and
number
ustwo
there
chlorine
and
are
types
2number
molecules
atoms
atoms
on
of
the
sodium
on
product
chloride.
side.
side.
2tells
on
chlorine,
same
atoms
sodium,
that
of
type
on
each
tells
are
and
tells
each
type
us
involved
usthat
side
that
onof
of
there
the
there
in
the
of
reactant
product
this
atoms
is
equation.
are
one
reaction.
2each
on
molecule
side.
side.
Na
both
atoms
So…
the
ofon
Each
molecule
has
Na
and
Cl.
There
You will
Let’s
are
chlorine
consider
2reactant
get
types
organized
the
that
of
both
reactant
and
atoms:
contains
coefficients
product
by1 creating
side.
Sodium
2 Cl
sides.
atoms.
&1a&subscripts
table
Chlorine
3 of 6
Prove a Chemical
Equation is Balanced
 Prove the equation is balanced.
MnO2 + 4HCl  MnCl2 + Cl2 + 2H2O
Atom
Mn
O
H
Cl
Reactant
1
2
4
4
Product
1
2
4
42
This
reaction
is
balanced
because
there
are
same
Chlorine
MnCl
There
are
tells
abalanced
us
total
up
there
inof
two
4ischemical
chlorine
one
products
molecule
atoms
MnCl
that
on
&
the
has
Cl
2H
O
tells
us
that
there
are
two
molecules
each
Remember,
4HCl
We
First:
need
Second:
Third:
tells
Identify
tells
akeep
that
Count
Count
us
the
track
that
there
all
the
the
of
there
of
are
number
number
the
types
four
isdifferent
one
and
equation
of
ofmolecule
atoms
numbers
atoms
elements
of
the
2 shows
2has
2.
2MnO
2tous
number
and
types
of
atoms
on
each
side.
Cl
1that
manganese
product
us
there
side
isbonded
1bonded
molecule
the
to
equation;
2to
of
chlorines.
chlorine
gas
oxygen
to
two
hydrogens.
having
same
atoms
of
type
one
on
of
each
are
this
and
hydrogen
each
type
involved
compound
number
side
on
of
bonded
the
in
the
ofreactant
product
this
and
atoms
equation.
reaction.
itone
has
on
side.
chlorine.
both
So…
the
2 tells
So,
2 from
with
there
Cl
is
MnCl
1Mn
atoms
atom
and
bonded
2to
from
2together.
Cl
the
Cl&
Sothere
there
are
four
hydrogen
and
two
Oxygen
You
So
There
one
will
Let’s
manganese
are
consider
are
get
reactant
42the
four
organized
types
both
hydrogen
and
of
bonded
coefficients
product
by and
creating
and
Mn,
two
sides.
four
&
oxygens.
O,
aatoms.
subscripts
chlorine.
H,
table
2atoms:
2. Cl
4 of 6
Prove a Chemical
Equation is Balanced
 Prove the following reaction is balanced.
2NO + 2CO  N2 + 2CO2
Atom
N
Reactant
2
Product
2
O
4
2
4
2
C
5 of 6
Prove a Chemical
Equation is Balanced
 Prove the following reaction is balanced.
P4O10 + 4HNO3  4HPO3 + 2N2O5
Atom
P
Reactant
4
Product
4
O
22
4
4
22
4
4
H
N
6 of 6
Prove a Chemical
Equation is Balanced
Home
 Prove the following reaction is balanced.
C6H12O6 + 6O2  6CO2 + 6H2O
Atom
C
Reactant
6
Product
6
H
12
18
12
18
O
Explain Reasons for
Balancing Equations
1 of 5
Home
 You know that a reaction is balanced when the
coefficients make the number and type of atoms on
each side of the equation equal.
2Na + Cl2  2NaCl
 You can also prove whether a reaction is balanced.
 But why is it so important to balance an equation?
 Why wouldn’t you want to write the equation like
this… Na + Cl2  NaCl
 There are at least three reasons why it is important
to balance a chemical reaction.
2 of 5
Explain Reasons for
Balancing Equations
 Look at the unbalanced equation below.
2 Na
Na Na
+ Cl2  2 NaCl
Cl Cl
Na Cl Na Cl
This
TheWhen
unbalanced
means
The
Notice
Where
the
Law
if Now
we
proper
there
did
ofequation
start
Conservation
that
we
are
coefficients
are
with
other
two
following
above
two
chlorine
chlorine
atoms
of
suggests
are
Matter.
atoms
in
go?
ofplace
chlorine
that an
It has
we
on
This
The
to
atom
must
the
go
and
law
Law
reactant
somewhere.
of
end
the
states
chlorine
ofwith
equation
Conservation
that
side
two
just
It
matter
but
atoms
iscan’t
disappeared.
balanced,
only
of
can
of
just
1Matter.
chlorine.
chlorine
not
disappear.
be
Thiscreated
leads
all us
the
orto
This
destroyed
atoms
on
a very
is
theagainst
can
product
important
only
be accounted
the
changed
side.
law.
law inin
for.
chemistry.
form.
3 of 5
Explain Reasons for
Balancing Equations
 Look at the partially balanced equation below.
2Fe + 3H2O 
Fe Fe
Fe2O3
+ 3 H2
O
O-Fe-O-Fe-O H-H
H H
H-H
O
O
H-H
H H H H
However,
As
Notice
Hydrogen
itWhat
turns
the
If
inhydrogens
athis
coefficient
out,
chemical
gas
partially
the
is odorless
hydrogen
from
equation
in balanced
front
water
and
atoms
of
is colorless
on
the
not
equation
the
bonded
H2 reactant
side
that
are
would
together
properly
the
not
iron
accounted
make
to
and
balanced,
but
form
this
the
explosive.
equation
for
another
oxygen
you
on the
may
are
product:
balance?
product
balanced.
miss side.
That’sWhere
not a product
did
aHydrogen
potential
those
you
hydrogen
would
Gas
product.
(Hwant
) to go?
overlook.
2atoms
Explain Reasons for
Balancing Equations
4 of 5
 What does the unbalanced reaction below tell you?
2 Na
+ Cl2 
Na Na
Cl-Cl
2 NaCl
Na-Cl Na-Cl
Balancing
The
This
Remember,
An
We
amounts
reaction,
unbalanced
know
the of
equation
chemical
the
aseach
written,
ingredients
equation
substance
tell
equations
tells
usishow
and
you
like
are
are
products
much
that
adetermined
recipe
recipes.
sodium
of each
reactant
atoms
They
but we
tell
(Na)
by
that
is
don’t
the
the
required
react
tells
amounts
coefficients
know
you
with
and
how
allchlorine
ofthe
how
much
the
that
ingredients
much
ingredients
are
gas
of each
assigned
molecules
of each
is
but
required
needed.
product
(Cl2)
to
doesn’t
and
form
thewhen
tell
molecules
amounts
you
the
will
how
equation
of
be
ofproduct
much
produced.
sodium
isofbalanced.
you
chloride
eachcan
oneexpect.
(NaCl)
to use
Explain Reasons for
Balancing Equations
5 of 5
Home
 Why is it important to work with a balanced
chemical equation?
 If an equation isn’t balanced, it implies that atoms
suddenly appear or disappear. This goes against
the Law of Conservation of Matter
 If an equation isn’t balanced, you may miss a
product that is not easily observed.
 An equation is a chemical recipe. If it isn’t
balanced, it is like a recipe that doesn’t include any
amounts. It would be useless to try to make
something from such a recipe.
Technical Science
Introduction to Chemistry
You have Completed
Chemical Equations
Created by John W. Pluemer