The Properties
of Gases
Properties of Gases
Gases expand to fill the container.
2. Gases take on the shape of the
container.
3. Gases are highly compressible.
1.
(Can be liquefied at high pressures).
Gases have low densities.
5. Gases mix uniformly.
4.
The Kinetic Molecular
Theory
The kinetic molecular theory
describes the behavior of
ideal gases.
An ideal gas is one that
conforms to the KMT.
1. Molecules are in constant
random motion
Temperature is proportional to the
average kinetic energy of the
2
molecules. KE = ½ mv
KE = ½ mass times speed squared
The speed is proportional to the
absolute temperature (Kelvin).
2. A gas is mostly empty space
Molecules are far apart from each
other. This accounts for the low
density and high compressibility.
The volume of the individual
molecules is negligible compared
to the volume of the gas.
3. No intermolecular forces
There are no attractive or repulsive
forces between gas molecules.
Adjacent molecules do not attract
or repel each other.
4. Collisions are elastic
When gas molecules collide with
each other they may speed up or
slow down, BUT …
The net (total) energy of the gas
molecules does not change.
Kinetic Molecular Theory
Gases in constant motion, speed
depends on temperature.
2. Molecules have negligible
volume.
3. No intermolecular forces.
4. Elastic collisions. No change in
energy.
1.
Temperature reminder
When doing calculations,
temperature must always be in
an absolute temperature scale …
… where the lowest possible
temperature is zero degrees.
Use Kelvin degrees!
Temperature conversion
K = C + 273
Pressure
1. Pressure is the force per unit
area exerted by the gas molecules.
2. Pressure is proportional to
the number of collisions
between the gas molecules and
the walls of the container.
Pressure
1. Pressure is a measure of the
force per unit area.
force
Pressure can be in P = area
pounds per square
inch (PSI), or …
2
… newtons per square meter (N/m )
pascal (Pa) =
2
N/m
Pressure
1. Pressure is a measure of the
force per unit area.
force
P=
Glass
tube
with
Hg
area
At sea level, air pressure
holds up a column of
mercury 760 mm high.
Bowl of Hg
Torricelli
Pressure Measurements
Standard sea level pressure is…
1.00 atmospheres (atm)
760 mm Hg
760 torr (from Torricelli)
101.3 kilopascals (kPa)
2
14.7 lb/in
Pressure Measurements
Standard sea level pressure is…
1.00 atmospheres (atm)
760 mm Hg
760 torr (from Torricelli)
101.3 kilopascals (kPa)
2
14.7 lb/in
Pressure
2. Pressure is proportional to the
number of collisions between the
gas molecules and the walls of
the container.
If you change the
number of
collisions, you
change the pressure.
Do the following conversions:
1.
2.
3.
4.
5.
Express 20.0 C in K.
What is 200. K in Celsius?
Convert 695 torr to atm.
Convert 0.952 atm to kPa.
Convert 500. kPa to atm.
Now do these conversions:
1.
2.
3.
4.
5.
Express -30.0 C in K.
What is 576 K in Celsius?
Convert 705 mm Hg to kPa.
Convert 3.50 atm to torr.
Convert 84.3 kPa to atm.