The word kinetic indicates motion.
The Kinetic Theory describes the
motion of gas particles.
The Kinetic Theory has
a few assumptions:
One assumption is that
the gas particles are
very tiny and spread
out. Therefore, a gas
is mostly EMPTY
Gas particles are
always in motion.
They bump into each
other and into the
walls of the container.
They undergo ELASTIC
• Elastic Collisions are
collisions that do NOT
lose or transfer
energy when they
Gas particles have
little or no attraction
for each other. They
don’t repel each other
• Not all gas particles have the same
amount of kinetic energy. Some are fast
and some are slow.
• The kinetic energy is proportional to the
temperature of the gas particles. When
the temperature is high, the particles have
more energy and move faster.
In a sealed container, the volume
and the pressure of a gas are
inversely proportional at constant
• Inversely proportional means that as the
volume goes up, the pressure goes down.
OR if the volume goes down, the pressure
Mathematically it looks like this:
V1P1 = V2P2
• Consider some gas
inside a jar. If the
volume of the jar is
500ml at a pressure
of 740mm Hg, what
will the volume be if
the pressure changes
to 1500mm Hg?
• V1P1 = V2P2
(500ml)*(740mm Hg) = (V2)*(1500mm Hg)
V2 = 246.7ml
• Try a second problem:
A balloon has a volume of 0.8 liters at a
pressure of 1.2 atm. What would be the
new pressure if the volume is increased to
Remember: V1P1 = V2P2
Answer: 0.417 atm
• Now let’s look at Pressure Volume
some data of 133 kPa 0.63 liters
pressure and volume
of a gas in a sealed 122 kPa 0.69 liters
container. 111 kPa 0.75 liters
• What happens to the 100 kPa 0.84 liters
volume of a gas when
88 kPa 0.95 liters
decreases? 77 kPa 1.09 liters
66 kPa 1.27 liters
That’s right, the volume increases!
Take a look at the
1 graph of the data, it
0.8 forms a beautiful
0 50 100 150
Let’s Review Boyle’s Law
• Use the equation V1P1 = V2P2 to solve
problems when the pressure and volume
change while the temperature is constant.
• A pressure vs. volume graph is in the
shape of a hyperbola.
• Don’t mix units, be consistent!
Standard pressure is a perfect day on the
beach, right at sea level. The values are:
101.3 kPa = 1.0 atm = 760 mmHg
Get your calculator, it’s time to go to Moodle
and do some Boyle’s Law Problems.