# Understand Gas Pressure

In this worksheet, students will revise the concept of gas pressure in relation to the Particle Model.

Key stage:  KS 3

Curriculum topic:   Physics: Matter

Curriculum subtopic:   Particle Model

Difficulty level:

### QUESTION 1 of 10

What would happen if you were to push a pin on its pointy end? You would hurt yourself, but why?

The pin would push on your finger so much that it would break the bonds between the cells and become physically inserted into your finger.

What would happen if you did the same, but this time with the flat end?

The pin would go into the wall, this time breaking the bonds of the atoms in the wall and making a nice snug home for itself.

Assuming you applied the same force in both cases, the end result would be different, because of the difference in pressure applied to your thumb.

In the first case, the force is concentrated on a very small area, so the pressure is very high. In the second, the force is spread out over a larger area, so the pressure is lower.

The formula used to calculate pressure is:

Pressure = force / area

When the force is in Newton (N) and the area in m2, the unit for pressure is Pascal (Pa) or N/m2.

If the area is in cm2, then the pressure is measured in N/cm2.

This means that if you increase the force then the pressure goes up.

Pressure = force divided by area; this means that pressure is inversely proportional to pressure.

This means that as area increases, pressure decreases.

Use your imagination to visualise how gas particles collide into the walls of the containers in the diagram below. Each time they hit the walls of the container; they push them a little bit. This is where our force comes from in the equation pressure = force/area.

In this example, the second container has a smaller volume, but the number of particles is the same, so the particles collide more. Remember, every time there is a collision, there is a small force – so if there are more collisions, the total force increases.

Boyle's Law is used to calculate how much pressure changes when the volume of a gas changes, provided the temperature and mass of the gas stay the same:

P1 × V1 = P2 × V2

P1 and V1 is the pressure and volume at the start, and P2 and V2 are the final pressure and volume of the gas.

If you rapidly change the volume of the container, then you will change the pressure as well as there will be more collisions in a smaller area – both of these are conditions for higher pressure.

Why would you hurt yourself if you pushed a pin on its pointy end?

The force is concentrate on the tip of the pointy part of the pin

The pressure on the pointy end is smaller

Calculate the pressure if a force of 238.0 N is applied to an area of 2.3 m2.

103.5 Pa

103.4782 Pa

What happens to gas pressure when the volume is reduced?

It increases

It decreases

It stays the same

If you were to increase the temperature of a gas, what do you think would happen to the pressure?

The pressure would increase

The pressure would decrease

If a system has an initial pressure of 5 Pa in a volume of 3 m3 and is then compressed to a pressure of 8 Pa, what would the new volume be?

The answer must be given to an appropriate number of decimal places.

2m3

1.875m3

Choose the appropriate word to complete the sentence below.

Gases are ___________.

Compressible

In-compressible

What is the atmospheric pressure on the surface of the Earth (at sea level)?

1000 Pa

10,000 Pa

100,000 Pa

What happens to atmospheric pressure at high altitudes?

It increases

It decreases

It stays the same

What determines pressure in gases?

Volume

Temperature

The collision of particles

Use Boyle's Law to calculate the pressure inside a 200 cm3 balloon, if the initial pressure is 7 N/cm3 and you squash it to 140 cm3.

1540 N/cm³

1000 N/cm³

10 N/cm³

• Question 1

Why would you hurt yourself if you pushed a pin on its pointy end?

The force is concentrate on the tip of the pointy part of the pin
EDDIE SAYS
The force would be concentrated on a very small area making the pressure would be very high. Area and force are inversely proportional, the smaller the area the greater the force.
• Question 2

Calculate the pressure if a force of 238.0 N is applied to an area of 2.3 m2.

103.5 Pa
EDDIE SAYS
Force = 238.0N Area = 2.3 m2 Force = 238.0 / 2.3 Force = 103.4782 The question is given to 1 decimal place so your answer should also be given to 1 decimal place. Force = 103.5 Pa - remember the unit!
• Question 3

What happens to gas pressure when the volume is reduced?

It increases
EDDIE SAYS
In a gas, the more collisions you have per unit area, the more pressure you have. By reducing the volume, you are increasing the number of collisions per unit area. Therefore, pressure increases!
• Question 4

If you were to increase the temperature of a gas, what do you think would happen to the pressure?

The pressure would increase
EDDIE SAYS
A temperature increase would mean that the particles are moving faster. This would, in turn, mean that there would be more collisions with a higher force - this all points to the pressure going up!
• Question 5

If a system has an initial pressure of 5 Pa in a volume of 3 m3 and is then compressed to a pressure of 8 Pa, what would the new volume be?

The answer must be given to an appropriate number of decimal places.

2m3
EDDIE SAYS
V1 x P1 = V2 x P2 Work out the left-hand side first: V1 = 3 m3 P1 = 5 Pa V1 x P1 = 15 Rearrange the equation: 15 = V2 x P2 15/P2 = V2 Put in the final numbers P2 = 8 15/8 = V2 V2 = 1.875‬ m3 Don't forget to round!
• Question 6

Choose the appropriate word to complete the sentence below.

Gases are ___________.

Compressible
EDDIE SAYS
Gases can be squashed; they are compressible - this is why we need to consider Boyle's law when looking at gases and pressure. You're making fantastic progress! Let's push on.
• Question 7

What is the atmospheric pressure on the surface of the Earth (at sea level)?

100,000 Pa
EDDIE SAYS
The atmospheric pressure on the surface of the Earth is 100,000 Pa. This question required some guesstimation! So don't worry if you struggled.
• Question 8

What happens to atmospheric pressure at high altitudes?

It decreases
EDDIE SAYS
Imagine there is a massive column of air 15 miles high pressing down on you, squashing the air. We know that when air is squished it increases in pressure. Therefore, at high altitudes, air pressure decreases.
• Question 9

What determines pressure in gases?

The collision of particles
EDDIE SAYS
Gas pressure is caused by the number of collisions of gas particles. Whilst volume and temperature can impact the pressure - it is only the collisions of the particles against the walls that determine gas pressure.
• Question 10

Use Boyle's Law to calculate the pressure inside a 200 cm3 balloon, if the initial pressure is 7 N/cm3 and you squash it to 140 cm3.

10 N/cm³
EDDIE SAYS
P1 x V1 = P2 x V2 200 x 7 = P2 x 140 P2 = 1400 / 140 = 10 N/cm³ Wow, this activity was incredibly challenging. Take a much-needed break before you attempt another worksheet science-whiz!
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