New
New
Year 10
•
OCR
•
Foundation
Explaining pressure changes
I can explain the effect of a temperature change or a change in volume on the pressure of a gas.
New
New
Year 10
•
OCR
•
Foundation
Explaining pressure changes
I can explain the effect of a temperature change or a change in volume on the pressure of a gas.
Lesson details
Key learning points
- The pressure of a gas in a container increases if the temperature or amount of gas increases, or volume decreases.
- Increasing temperature increases the speed of particles in a gas.
- Pressure × volume = constant (pV = constant).
- When a gas expands, its particles do work on the surrounding air.
Common misconception
Pressure is a weight or a force; and pressure has a preferred downwards direction in a liquid or gas.
Use the particle model to provide opportunities for pupils to explain the causes of pressure in a gas that is in a container, and to explain how the difference in pressure between inside and outside causes an outward force.
Keywords
Particle model - a scientific model using the idea of moving particles to explain the behaviour of matter.
Pressure - caused by a force acting over an area on a surface; it can be calculated using: pressure = force ÷ area
A gas or liquid exerts a pressure. Don't say: A gas or liquid has pressure.
Teacher tip
Licence
This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
Video
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Starter quiz
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6 Questions
Q1.
Which of the following show a definition of work or a unit of work?
Correct answer: J
J
N
force exerted when energy makes an object move
Correct answer: energy transferred when a force makes an object move
energy transferred when a force makes an object move
Q2.
Which of the following show a definition of pressure or a unit of pressure?
a type of force
Correct answer: force per unit area
force per unit area
force per unit volume
N
Correct answer: N/m$$^2$$
N/m$$^2$$
Q3.
Which of the following are equal to 1 kN?
0.001 N
Correct answer: 0.001 MN
0.001 MN
1000 mN
Correct answer: 1000 N
1000 N
1 000 000 N
Q4.
If the particles in a gas are pushed closer together, the pressure of the gas increases. Which of the following explains why?
Correct answer: Particles collide with each other more often.
Particles collide with each other more often.
Some of the particles stick together.
The particles are squashed so they become smaller.
The particles repel each other more strongly all the time.
Q5.
A table of weight 500 N stands on the floor. The area of contact between the table and the floor is 200 cm$$^2$$. The pressure exerted by the table on the floor is __________ N/cm$$^2$$.
0.40
Correct answer: 2.5
2.5
500
700
1000
Q6.
A sealed container in the shape of a cube contains gas. Which of the following statements are correct?
Correct answer: pressure of gas = force on one inner face of cube ÷ area of one face
pressure of gas = force on one inner face of cube ÷ area of one face
pressure of gas = force on one inner face of cube ÷ total area of all faces
The gas exerts pressure because its weight pushes down on the container’s base.
Correct answer: The gas exerts pressure because its particles exert forces on all inner faces.
The gas exerts pressure because its particles exert forces on all inner faces.
Exit quiz
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6 Questions
Q1.
Which of the following statements about the particle model are correct?
Correct answer: It can be used to explain how matter behaves.
It can be used to explain how matter behaves.
Correct answer: It can be used to predict how matter will behave.
It can be used to predict how matter will behave.
The model is made of diagrams or animations.
It says that particles move in liquids and gases but not in solids.
Correct answer: It says that particles in solids, liquids and gases are always moving.
It says that particles in solids, liquids and gases are always moving.
Q2.
A child blows air into a balloon. Order the statements to describe and explain what happens.
1 - There are more particles inside, so their collisions become more frequent.
1
- There are more particles inside, so their collisions become more frequent.
2 - This increases the outward forces exerted by the air on the balloon.
2
- This increases the outward forces exerted by the air on the balloon.
3 - The outward forces are now greater than the inward forces.
3
- The outward forces are now greater than the inward forces.
4 - This makes the balloon expand, which increases the volume inside it.
4
- This makes the balloon expand, which increases the volume inside it.
5 - The particles inside are now more spread out, so collisions are less frequent.
5
- The particles inside are now more spread out, so collisions are less frequent.
6 - This decreases the pressure on the inside of the balloon.
6
- This decreases the pressure on the inside of the balloon.
7 - Expansion stops when this balances the air pressure outside.
7
- Expansion stops when this balances the air pressure outside.
Q3.
A gas expands by exerting an average force of 500 N on a piston. This pushes the piston through a distance of 4.0 cm in the direction of the force. The work done by the gas on the piston is J.
Correct Answer: 20, 20 J, 20J, twenty, twenty joules
20, 20 J, 20J, twenty, twenty joules
Q4.
When some gas is released from a container, the gas expands rapidly. Which of the following statements are correct?
Correct answer: The gas cools as it expands.
The gas cools as it expands.
The gas heats up as it expands.
The surrounding air does work on the gas.
Correct answer: The gas does work on the surrounding air.
The gas does work on the surrounding air.
Q5.
The volume of a sealed container of gas is halved. Which of the following statements describe what happens to the gas after the decrease in volume?
The particles take more time between collisions, on average.
Correct answer: The particles travel less far between collisions, on average.
The particles travel less far between collisions, on average.
Correct answer: The particles collide more often with each cm$$^2$$ of the container's surface.
The particles collide more often with each cm$$^2$$ of the container's surface.
Correct answer: The pressure of the gas on the container increases.
The pressure of the gas on the container increases.
The pressure of the gas in the container halves.
Q6.
A container of gas at a pressure of 80 kN/m$$^2$$ has a volume of 0.050 m$$^3$$. What is the pressure when the container expands to a volume of 0.075 m$$^3$$?
4.0 kN/m$$^2$$
Correct answer: 53 kN/m$$^2$$
53 kN/m$$^2$$
120 kN/m$$^3$$
4000 kN/m$$^3$$
53 000 kN/m$$^2$$