Title – Gas
Pressure
Success Criteria
Bronze – Draw a particle
diagram for a gas
ALL
State the factors which
affect gas pressure
MOST
Describe how factors
affect gas pressure
SOME
Explain why a can crushes
due to pressure
Silver – explain how
particles move in a gas
Gold – explain what is
meant by concentration
Gases have enough kinetic energy to move around, the molecules
are not bonded
Gases have ‘Brownian motion’ a random movement of particles
caused by collisions
Pressure
Which
Pressure
means
is the
how
force
hardexerted
are particles
on a
hitting the certain
outside area
of a container?
Gas particles moving
around in a container
exert a certain amount
of force on the outside
of the container
What effects pressure?
Heat
Concentration
Heat
Heat gives particles more
kinetic energy so they move
around quicker
Faster collisions means
higher pressure
Concentration
Particles collide – the more
particles in an area the
more they bump into each
other
More collisions means
higher pressure
Density
Density = mass
per unit volume
Or… how much
stuff do you
have in a given
area
Why does my can crush?
Heat means more kinetic energy, so
bigger collisions so increase in
pressure
Cold water quickly cools down particles,
big decrease in pressure, now more
pressure from outside so it gets pushed in
Can being pushed outwards by
particles colliding with the can
Watch these videos
Explain why the tanker imploded
• In your answer you
should talk about
• Thermal energy
• Kinetic energy
• Collisions with the
container
• Pressure
• Internal pressure and
atmospheric pressure
– As the car is heated, thermal energy turns to
kinetic energy as particles start to move around
more
– The internal pressure increases as the collisions
with the outside are more frequent and larger
– As the car is sealed these particles cannot
escape.
– When the car is exposed to the water the
particles cool down rapidly, causing the internal
pressure to drop
– There is a greater number of particles colliding
on the outside of the car compared to the inside
of the car,
– Therefore, the outside pressure crushed the car.
Atmospheric
pressure
The air around your
body exerts a force on
your body – this is called
atmospheric pressure
Gravity pulls all particles
to the ground, so more
particles more pressure
Extension –
Explain how temperature
affects pressure. Use the
key word ‘kinetic energy’ in
your answer
Title – Gas
Pressure
Success Criteria
ALL
State the factors which
affect gas pressure
MOST
Describe how factors
affect gas pressure
SOME
Explain why a can crushes
due to pressure
Bronze – what is pressure?
Silver – how can we
increase pressure in a
sealed container?
Gold – what is atmospheric
pressure
Pressure = force per unit area
Boyle’s Law
Gas, pressure and volume all link
In a sealed container with fixed
temperature – the gas pressure
is caused by the collisions
If you decrease the volume the
pressure increases
How else can you increase the
pressure?
Boyle’s Law
Boyle’s law states:
"For a fixed mass of gas, at a constant temperature, the product of
pressure and volume is equal to a constant.“
The volume of a fixed mass of gas, at constant temperature, is
inversely proportional to the pressure.
Pressure x Volume = Constant
P
x
V
= Constant
Using Boyle’s Law
Worked Example:
Pressure x Volume = Constant
P
x
V
= Constant
In an experiment, 200 cm3 of gas was collected in a flask at a pressure of 125 kPa.
Calculate the volume of this mass of gas at a pressure of 100 kPa and the same temperature.
Solution:
P1 = 125 kPa and V1 = 200 cm3
So P1 x V1 = constant
125 x 200 = 25,000
P2 = 100 kPa and V2 needs to be worked out
Rearrange equation to find Volume
V2 = Constant ÷ P2
Constant ÷ Pressure = Volume
25,000 ÷ 100 = 250 cm3
Graph
100
X
Data
X
X
X
2
4
6
Data
10
What is wrong
with this graph?
1. Plot the graph of this data
2. Describe the relationship shown in the graph
(2)
As temperature increases, pressure increases [1];
linearly [1]
3. Describe the movement of particles in a gas (2)
Particles are far apart (relative to their size) [1];
and moving freely/rapidly [1].
They produce random collisions [1]
They have lots of kinetic energy [1]
4.. Explain why the pressure on a container wall increases as the
temperature of the gas increases (4)
Thermal energy gives particles more kinetic energy [1]
Particles move faster / gain kinetic energy (but do not move farther apart
since container volume is fixed).
Particles hit container walls more frequently [1];
and with more force (so average force per unit area, i.e. pressure, increases)
[1].
5. Explain what happens to a balloon, if it is taken underwater
(4).
Water has higher pressure than air [1]
exerts a force on all sides of the balloon that is greater than in air [1]
The pressure from the water causes the air to compress inside the
balloon.[1]
The deeper the balloon is taken into the water, the greater the pressure,
and therefore, the smaller the balloon will become. [1]
The pressure from the water will compress the balloon until the air
pressure within the balloon can supply an equal amount of force against the
water [1]
6.. A gas has a volume of 100 cm3and a pressure if 145Pa, what is the
constant?
Pressure x Volume = constant
100 x 145 = constant
Constant = 14,500
6b. Use this answer to work out what happens when you
increase the volume and decrease the volume
As volume increases the pressure decreases
As volume decreases the pressure increases
7. A gas is compressed from a volume of 75 cm3 to a volume of
30 cm3 its temperature remains the same. The pressure of the
gas after it has been compressed is 110 Pa. What was the
pressure of the gas before it was compressed?
After compression; PV = constant, 30 x 110 = 3,300
Before compression; PV = constant, P x 75 = 3,300
P = 3,300 ÷ 75 = 44 Pa