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```The Gas Laws
Lesson 1 : Boyle’s
Law
Lesson Objectives
• State the relationship between the pressure
and volume of a fixed mass of gas, at constant
temperature
• P∝1/V
or
P1V1 = P2 V2
• Carry out calculations using this relationship
Pressure and Volume
Low P,
large V
P x V is constant
High P,
small V
Boyle’s Law
• For a fixed mass of gas at a constant
temperature, the volume of the gas is
inversely proportional to the pressure
• If the pressure is doubled, the volume is
halved; if the pressure is tripled, the
volume is reduced to one-third, etc.
• This can be mathematically written in
these three ways:
• P ∝ 1 / V P x V = constant P1V1 = P2 V2
•
This relationship is called Boyle’s law
Boyle’s Law
Experiment
• This is the
demonstration
you will see to
investigate
Boyle’s Law
Volume
scale
Gas
(air)
Pressure
Gauge
P – V Graph
P∝1/V
• This is the
typical curve
for two
variables
which are
inversely
proportional
to each
other
A moving version!
P∝1/V
(cm3)
(Pa)
Note : the
temperature
is constant!
A More Tricky graph….
P (Pa)
P∝1/V
1/V
(1 / cm3)
• If you plot a
graph of P
against 1 / V,
you will get a
straight line
through the
origin. This is
the proof that
P and V are
inversely
proportional
Some Results
Pressure (kPa)
Volume (cm3)
50
1000
100
500
150
330
200
250
250
200
1/V
Use these results to get P – V and P - 1/V
graphs like the ones in the previous slides
Boyle’s Law
The volume of
a gas is
inversely
proportional to
its pressure if
temperature is
constant
Robert
Boyle
Try Some Questions
1. A bubble of air released by a SCUBA diver
has a volume of 6cm3 when released under
water where the pressure is 3 atmospheres
(300 kPa). What is the volume of the bubble
when it reaches the surface where the
pressure is 1 atmosphere (100 kPa)?
2. The fuel mixture in the cylinder of a car
engine has a volume of 400cm3 at a
pressure of 100kPa. It is then compressed
until its volume is reduced to 50cm3. What
is the new pressure?
Lesson 2 : The
Pressure Law
Lesson Objectives
• State the relationship between the pressure and
temperature of a fixed mass of gas, at constant
volume (s)
• P∝T
or
P1 / T1 = P2 / T2 (s)
• Carry out calculations using this relationship (s)
• Explain how this relationship leads to the kelvin
temperature scale (s)
• Convert between temperatures in kelvin and °C
(s)
Pressure Law
Constant
volume
Low particle
energy
High particle
energy
• The
pressure of
a gas
increases
when the
temperature
increases, if
the volume
stays
constant
Pressure law
Pressure Law apparatus
• This is the
apparatus
used to
investigate
the
relationship
between
temperature
and pressure
of a gas at
constant
volume
Pressure-Temperature Graph
• If temperature is in °C the graph is linear,
but not through the origin
At -273°C the
pressure
(theoretically)
would be zero. This
means that the
particles have zero
kinetic energy.
- 273°C
P (kPa)
T (°C)
Kelvin Temperature Scale
• The pressure-temperature graph suggests that
a true zero of temperature is at -273°C
• This is known as absolute zero
• Lord Kelvin used this to invent a new scale of
temperature called the kelvin scale
• Absolute zero is zero kelvin (0K) which is the
same as -273°C
• To change temperatures from °C to K you add
273
• To change temperatures from K to °C you
subtract 273
Kelvin and Celsius
Try These
Change these to kelvin
1. 0°C
2. 100°C
3. 27°C
4. -20°C
Change these to °C
1. 0K
2. 100K
3. 273K
4. 1000K
1.
2.
3.
4.
1.
2.
3.
4.
273K
373K
300K
253K
-273°C
-173°C
0°C
727°C
Another P – T Graph
• If the
temperature is
measured in
kelvin, the
graph passes
through the
origin
• In other words,
pressure is
directly
proportional to
temperature (in
kelvin)
P (Pa)
P∝T
T (K)
The moving version!
(Pa)
(K)
P∝T
The Pressure Law
• For a fixed mass of gas at a constant
volume, the pressure of the gas is directly
proportional to the temperature (in kelvin)
• If the temperature is doubled, the pressure
is doubled; if the temperature is tripled, the
pressure is tripled, etc.
• This can be mathematically written in these
three ways:
• P ∝ T P ÷ T = constant P1 ÷ T1 = P2 ÷ T2
```