Section
4.2
pg.
163‐168
Curriculum
Objectives:
1.  Describe
and
compare
the
behaviour
of
real
and
ideal
gases
in
terms
of
the
kinetic
molecular
theory.
2.  Explain
the
law
of
combining
volumes.
 
The
central
idea
of
the
kinetic
molecular
theory
is
that
the
smallest
entities
of
a
substance
are
in
continuous
motion.
 
These
entities
may
by
atoms,
ions
or
molecules.
 
As
they
move
about,
the
entities
collide
with
each
other
and
with
objects
in
their
path.
Observation
of
microscopic
particles,
such
as
a
pollen
grain,
shows
a
continuous,
random
motion.
This
is
known
as
Brownian
motion,
named
for
Scottish
scientist,
Robert
Brown.
 
According
to
Kinetic
molecular
theory,
the
motion
of
molecules
is
different
in
solids,
liquids
and
gases.
  Solids
‐
primarily
vibrational
motion.
  Liquids
‐
vibrational,
rotational
and
some
translational
motion
  Gases
–
the
most
important
form
of
motion
is
translational
 
Kinetic
Molecular
Theory
explains:
1.  Gases
are
compressible
(due
to
most
of
a
sample
of
gas
being
unoccupied
space,
thus
particles
can
be
forced
closer
together)
2.  Gas
pressure
(due
to
pressure
being
the
result
of
particle
collisions
distributed
over
walls
of
a
container
causing
a
force
per
unit
area)
3.  Boyle’s
Law
(due
to
reduced
volume,
there
is
a
shorter
distance
between
walls
thus
more
frequent
collisions,
causing
increased
pressure)
4.  Charles’
Law
(due
to
increase
in
temperature,
there
is
an
increase
in
particle
speed
causing
more
collisions
with
the
wall.
The
wall
moves
outward,
thus
volume
increases)
  Try
pg.
164
#1
a),
d),
e)
a)
According
to
the
k.m.t.,
as
the
temperature
increases,
the
average
speed
of
the
gas
particles
increases.
If
the
volume
is
kept
constant,
then
faster‐moving
particles
will
collide
more
often
with
the
sides
of
the
container.
More
collisions
mean
a
greater
pressure.
d)
According
to
the
k.m.t.,
gases
such
as
air
are
very
compressible
because
most
of
the
volume
is
empty
space.
The
fact
that
there
is
very
little
empty
space
between
the
molecules
of
a
liquid,
such
as
oil,
makes
liquids
not
compressible.
In
a
hydraulic
system,
the
pressure
applied
at
one
end
(e.g.,
brake
pedal)
needs
to
be
transmitted
to
the
other
end
(e.g.,
brakes).
This
will
work
only
if
the
medium
inside
the
system
is
not
compressible.
e)
A
bullet
moves
in
a
straight
line
over
a
long
distance
before
it
hits
its
target.
According
to
the
k.m.t.,
a
gas
molecule
moves
only
a
very
short
distance
before
colliding
with
another
gas
molecule,
and
thus
changing
its
direction.
Section
4.2
Pg.
164
‐
166
Joseph
Gay‐Lussac
Amedeo
Avogadro
 
The
kinetic
molecular
theory
explains
many
physical
properties
of
gases.
But
what
about
their
chemical
properties?
 
In
1809,
Joseph
Gay‐Lussac,
a
colleague
of
Jacques
Charles,
measured
the
relative
volumes
of
gases
involved
in
chemical
reactions.
 
His
observations
led
to
the
Law
of
Combining
Volumes,
which
states
that:
  “When
measured
at
the
same
temperature
and
pressure,
volumes
of
gaseous
reactants
and
products
of
chemical
reactions
are
always
in
simple
ratios
of
whole
numbers”
  This
is
also
known
as
the
Gay‐Lussac’s
Law
 
A
simple
example
of
this
is
the
decomposition
of
liquid
water,
in
which
the
volumes
of
hydrogen
and
oxygen
gas
are
always
produced
in
a
2:1
ratio
 
Which
side
is
Hydrogen?
2H2O(l)

2H2(g)
+
O2(g)
 
Two
years
after
Gay‐Lussac’s
Law,
Avogadro
proposed
an
new
explanation
in
terms
of
numbers
of
molecules
  Avogadro
proposed:
“equal
volumes
of
gases
at
the
same
temperature
and
pressure
contain
equal
numbers
of
molecules”
  This
means
the
mole
ratios
provided
by
a
balanced
equation
are
also
the
volume
ratios.
  This
in
now
best
called
Avogadro’s
Theory
 
When
all
gases
are
at
the
same
temperature
and
pressure,
the
law
of
combining
volumes
provides
an
efficient
way
of
predicting
the
volumes
of
gases
in
a
chemical
reaction.
Coefficients:
1
3
2
Chemical
Amounts:
1
mol
3
mol
2mol
Volumes:
1
L
3
L
2
L
Example:
2
mL
6
mL
VH2: 2 ml x ( 3 ) =
1
6 mL
VNH3: 2 ml x ( 2 ) =
1
4 mL
4
mL
Use
the
law
of
combining
volumes
to
predict
the
volume
of
oxygen
required
for
the
complete
combustion
of
120
mL
of
butane
gas
from
a
lighter.
1)
The
first
step
is
to
write
the
balanced
chemical
equation,
including
what
you
are
given
and
what
you
need
to
find:
2C4H10(g)
+
13O2(g)
→
8CO2(g)
+
10H2O(g)
120
mL
V
=
?
2)
From
this
chemical
equation
you
can
see
that
13
mol
of
oxygen
is
required
for
every
2
mol
of
butane.
Therefore,
the
volume
of
oxygen
has
to
be
greater
than
120mL
by
a
factor
of
13/2.
VO2: 120 ml C4H10 x ( 13 mL O2)
2 mL C4H10
= 780 mL
To
make
sure
that
the
ratio
is
used
in
the
correct
order,
you
could
include
the
chemical
formula
with
each
quantity
as
shown
above.
Note
the
cancellation
of
the
units
and
chemical
formulas
A
catalytic
converter
in
the
exhaust
system
of
a
car
uses
oxygen
(from
the
air)
to
convert
carbon
monoxide
to
carbon
dioxide,
which
is
released
through
the
tailpipe.
If
we
assume
the
same
temperature
and
pressure,
what
volume
of
oxygen
is
required
to
react
with
125L
of
carbon
monoxide
during
a
100
km
trip?
1)
The
first
step
is
to
write
the
balanced
chemical
equation,
including
what
you
are
given
and
what
you
need
to
find:
2CO(g)
+
O2(g)
→
2CO2(g)
125
L
V
=
?
2)
From
this
chemical
equation
you
can
see
that
1
mol
of
oxygen
is
required
for
every
2
mol
of
carbon
monoxide.
Therefore,
the
volume
of
oxygen
has
to
be
less
than
125L
by
a
factor
of
1/2.
VO2: 125 L CO x ( 1 L O2)
2 L CO
= 62.5 L O2
According
to
the
law
of
combining
volumes,
62.5L
of
oxygen
is
required.
  This
equivalence
between
the
chemical
amounts
(coefficients)
and
the
volumes
only
works
for
gases,
and
only
if
they
are
at
the
same
temperature
and
pressure.
  Pg.
166
#5‐7
  Pg.
168
#5