Kinetic-Molecular Theory
•
•
Explains the behavior (properties) of gases
(chaos)
Assumes 5 things about:
1. Gas particles do not attract or repel each
other.
2. Gas particles are much smaller than the
distances between them.
3. Gas particles are in constant, random
motion.
4. Collisions with walls of a container or other
gas particles are elastic.
5. All gases have the same average kinetic
energy at a given temperature.
Ideal vs. Actual Gases
• Gases don’t behave exactly the way
scientists predict with the k-mt but it’s
close.
• Main factors to consider about a gas:
1. number of gas particles
2. volume of gas
3. temperature of gas
4. pressure of gas
• These 4 factors influence each other in
predictable ways.
• Boyle’s Law: relationship between pressure
& volume
• Charles’ Law: relationship between volume &
temperature
• Gay-Lussac’s Law: relationship between
temperature & pressure
• For each of the above decide:
– Inverse or direct relationship?
– What would graph look like?
– Formula for finding unknown variable?
Try It
1. The volume of a gas at 99.0 kPa is 300.0 mL.
If the pressure is increased to 188 kPa, what
will be the new volume?
2. A gas at 89o C occupies a volume of .67 L. At
what Celsius temperature will the volume
increase to 1.12 L?
3. A gas in a sealed container has a pressure of
125 kPa at a temperature of 30.0o C. If the
pressure in the container is increased to 201
kPa, what is the new temperature?
Answers
1. P1V1 = P2V2
99.0 x 300.0 = 188 x V2
158 mL
2. V1/T1 = V2/T2
.67 L / 362 K = 1.12 L / T2
332 o C
3. P1/T1 = P2/V2
125 kPa / 303 K = 201 kPa / T2
487 K or 214 o C
Combined Gas Law
• All 3 gas laws in one. All 3 factors may
vary or one may be held constant.
P1V1 / T1 = P2V2 / T2
• Why aren’t weather balloons fully inflated
before they are released?
Try It
1. A helium-filled balloon at sea level has a
volume of 2.1 L at .998 atm and 36o C. If it is
released and rises to an elevation at which the
pressure is .900 atm and the temperature is
28o C, what will be the new volume of the
balloon?
2. At 0.00o C and 1.00 atm pressure, a sample of
gas occupies 30.0 mL. If the temperature is
increased to 30.0o C and the entire gas sample
is transferred to a 20.0 mL container, what will
be the gas pressure inside the container?
Answers
1. .998 atm x 2.1 L
------------------------------------
.900 atm x V2
=
309 K
V2 = 2.27 L
301 K
2. 1.00 atm x 30.0 ml
------------------------------------
273 K
P2 = 1.66 atm
----------------------------------
P2 x 20.0 ml
=
----------------------------------
303 K