KINETIC THEORY
The word kinetic indicates motion.
The Kinetic Theory describes the
motion of gas particles.
KINETIC THEORY
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
SPACE.
KINETIC THEORY
Another assumption:
Gas particles are
always in motion.
They bump into each
other and into the
walls of the container.
They undergo ELASTIC
collisions!
KINETIC THEORY
• Elastic Collisions are
collisions that do NOT
lose or transfer
energy when they
collide.
Gas particles have
little or no attraction
for each other. They
don’t repel each other
either.
KINETIC THEORY
• 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.
BOYLE’S LAW
In a sealed container, the volume
and the pressure of a gas are
inversely proportional at constant
temperature.
BOYLE’S LAW
• Inversely proportional means that as the
volume goes up, the pressure goes down.
OR if the volume goes down, the pressure
goes up.
Mathematically it looks like this:
V1P1 = V2P2
BOYLE’S LAW
• Consider some gas
particles trapped
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
BOYLE’S LAW
(500ml)*(740mm Hg) = (V2)*(1500mm Hg)
V2 = 246.7ml
BOYLE’S LAW
• 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
2.3 liters?
Remember: V1P1 = V2P2
Answer: 0.417 atm
• Now let’s look at
some data of
pressure and volume
of a gas in a sealed
container.
• What happens to the
volume of a gas when
the pressure
decreases?
Pressure
Volume
133 kPa
0.63 liters
122 kPa
0.69 liters
111 kPa
0.75 liters
100 kPa
0.84 liters
88 kPa
0.95 liters
77 kPa
1.09 liters
66 kPa
1.27 liters
That’s right, the volume increases!
Volume (liters)
Boyle's Law
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Take a look at the
graph of the data, it
forms a beautiful
hyperbola.
0
50
100
Pressure (kPa)
150
That’s right, the volume increases!
Volume (liters)
Boyle's Law
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Take a look at the
graph of the data, it
forms a beautiful
hyperbola.
0
50
100
Pressure (kPa)
150
How can this graph be used??????
Volume (liters)
Boyle's Law
1.4
1.2
1
0.8
0.6
0.4
0.2
0
The graph is useful.
Notice the horizontal
line at 0.7 liters shows
that is equivalent to
about 124kPa.
0
50
100
Pressure (kPa)
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
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.