IT’S A GAS…
The Nature of Gases
Gases have some interesting characteristics
that have fascinated scientists for 300 years.
The first gas to be studied was air & it was a
long time before it was discovered that air
was actually a mixture of particles rather
than a single gas.
Although air is a mixture of several different
gases, it behaves much the same as any
single gas.
Kinetic Molecular Theory
The Kinetic Molecular Theory of Matter. Is
used to explain the behaviors and
characteristics of ideal gases
The theory states that the tiny particles in all
forms of matter are in constant motion.
There are 5 basic assumptions of the KMT
as it applies to ideal gases.
• Ideal gases are “perfect” gases that are
used as a model to describe characteristics
of real gases.
KMT Assumption #1
A gas is composed of small hard particles.
The particles have an
insignificant volume and
are relatively far
apart from one another.
There is empty space
between particles.
KMT Assumption #2
All collisions a gas particle undergoes are
perfectly elastic.
They exert a pressure but don’t lose any
energy during the collisions.
KMT Assumption #3 & #4
The particles in a gas move in constant
random motion.
Particles move in straight paths and are
completely independent of each of other
Particles path is only
changed by colliding with
another particle or the
sides of its container.
No attractive or repulsive
forces between particles.
KMT Assumption #5
All gas particles at the same temperature
have the same kinetic energy
K.E. = ½ (mass) (velocity)2
The speed of a molecule is
Directly related to its Kelvin
Temperature
The Nature of Gases
Regardless of their chemical identity, gases
tend to exhibit similar physical behaviors
Gas particles can be monatomic (Ne),
diatomic (N2), or polyatomic (CH4) – but they
all have some common properties:
The Nature of Gases
Common Properties of all gasses.
1. Gases have a small mass but can take a
large volume. (Low Density)
2. Gases can be squeezed
together.(Compressibility)
3. Gases fill their containers. (Expansion)
4. Gases diffuse. (Diffsion & Effusion)
5. Gases flow easily and without resistance
throughout their container. (Fluidity)
Gases have mass.
Gases “R” squeezable
If you squeeze any gas, its volume can be
reduced considerably
Gases have a low density
which allows for a lot
of empty space between
gas molecules.
Gases fill their containers
Gases expand until they take up as much
room as they possibly can.
Gases spread out to
fill containers until
the concentration of
gases is uniform
throughout the entire
space.
This is why that nowhere around you is
there an absence of air.
Gases diffuse
Gases can move through each other rapidly.
The movement of one substance through
another is called diffusion.
Because of all of the empty space between
gas molecules, another gas molecule can
pass between them until each gas is spread
out over the entire container, the gases mix
uniformly.
Gases flow past other gases!
If I opened up a bag
of popcorn in front of
the class you would
soon be able to
smell it in the back.
The popcorn smell
easily diffuses
throughout the other
gas molecules in the
room.
Diffusion or Effusion
When gas molecules randomly move about
a room it is called diffusion.
When gas molecules pass through a tiny
opening it is called effusion.
Some gases diffuse more rapidly
then other gases based on
their size and their energy.
The heavier and colder the gas
the slower it moves.
REAL Gases are almost IDEAL.
Real Gases act like IDEAL gasses at high
Temperatures and Low Pressures.
We live at relatively high
temperatures and Low pressures.
Real Gases differ from Ideal gases in that
real gas molecules have mass and they
have intermolecular forces effecting the
molecules themselves.
A Real Gas can change its State
• That empty space can be
compressed by pressure
allowing gas particles less
room to move around
thus decreasing the
volume while increasing
the Density.
• But be careful to much
pressure can change a
LIQUID
gas into a _________!
This is how your
shocks an struts work
in your car.
Gas variables
Experimental work in chemistry requires the
measurement of such quantities as volume,
temperature, pressure, and the amount of sample.
In order to describe a gas sample completely and then
make predictions about its behavior under changed
conditions, it is important to deal with the values of:
1) amount of the gas (# of moles)
2) volume
3) temperature
4) pressure