Ideal Gases (Edexcel IGCSE Physics)

A fission reactor is cooled with helium gas. The gas enters the reactor at 500°C.

What is this temperature in kelvin?

Helium gas enters the reactor at a pressure of 8.40 MPa and leaves the reactor at a temperature of 1170 K.

Calculate the pressure of the helium gas as it leaves the reactor.
[Assume the volume of the gas does not change.]

This question is about temperature and pressure in gases.

Describe what happens to the average kinetic energy of particles as the temperature decreases from 10 K towards 0 K.

Aneroid barometers are used to measure air pressure.

A student makes a model aneroid barometer as shown. 

The student heats the air in her can by placing the can in a water bath.  

Compressed air from a can is used to clean computer keyboards. 

Use ideas about particles to explain how a gas causes a pressure on the inside of a container.

The can has a warning sign on it. 

The can has a volume of 400 cm³ and the pressure of the compressed air inside is 5 times atmospheric pressure.

Calculate the volume that the air would occupy if it were all released to atmospheric pressure. 

Temperature can be measured using different scales.

Complete the table by inserting the missing temperatures. 

Some students measure the volume of a sample of gas at different temperatures.

The table below shows their results. 

The diagram shows some gas particles in a container.

The piston can be moved in or out to change the volume of the gas. 

Add arrows to the diagram to show the random motion of the gas particles. 

Explain how the motion of the gas particles produces a pressure inside the container. 

State what would happen to the pressure if you pushed the piston into the container without changing the temperature.

When the gas in the container is heated, the piston moves outwards. Place ticks (✓) against the three correct statements.

A hot air balloon is filled with air through an opening.

The air is heated using a burner. 

Describe the effect of an increase in temperature on the average speed of the air molecules.

The hot air causes a pressure on the inside of the balloon.

Use ideas about molecules to explain how the hot air causes this pressure.

Give a reason why the hottest air rises to the top of the balloon.

The average density of the hot air in the balloon is 0.95 kg/m³. The volume of this air is 2800 m³. 

As the balloon climbs higher, the air pressure outside it decreases. 

All gases above absolute zero exert a pressure on the walls of their container. 

State the value of absolute zero in °C. 

All gases above absolute zero exert a pressure on the walls of their container. 

Explain, in terms of its molecules, how a gas exerts a pressure on the walls of its container. 

A spray-can contains gas particles that are constantly moving. 

What happens to the average speed of the gas particles when the spray-can is warmed by the sun on a hot day?

The diagram shows a can that produces whipped cream using gas at high pressure. 

The volume of the high pressure gas container is 10 cm³.

The pressure of the gas is 10 000 kPa.

When the seal at S is broken, the gas is released into the space above the cream.

The gas expands to a total volume of 270 cm³. 

Calculate the new pressure of the gas. 

As the gas expands into the space above the cream, its temperature decreases. Using ideas about molecules, explain how this affects the pressure of the gas. 

Some of the gas molecules dissolve into the cream. 

The photograph shows a car tyre that needs to be inflated. 

                  Author: Ildar Sagdejev

The tyre exerts a pressure on the road of 270 kPa.

Use ideas about molecules to explain why the air inside the tyre exerts pressure. 

Air is pumped into the tyre to inflate it.

This increases the temperature and the pressure of the air in the tyre.

Use ideas about molecules to explain why the air pressure in the tyre increases. 

A diver breathes air from a cylinder when he is under water. 

A student wants to investigate how the volume of a balloon changes with pressure. 

A student blows up two balloons to the same size.

She puts one balloon into a freezer.

After a while, the student compares the two balloons.

The balloon that has been cooled is smaller. 

Use ideas about particles to explain why the cooled balloon is smaller.

The student decides to investigate the link between temperature and the size of the balloon.

She writes a plan. 

There are several faults in the student's plan.

Identify three of these faults and suggest an improvement to correct each one. 

A diver works in the sea on a day when the atmospheric pressure is 101 kPa and the density of the seawater is 1028 kg/m³. 

The diver uses compressed air to breathe under water.

1700 litres of air from the atmosphere is compressed into a 12-litre gas cylinder.

The compressed air quickly cools to its original temperature.

Calculate the pressure of the air in the cylinder.  

Assume that the atmospheric pressure remains at 101 kPa. 

As the diver breathes out, bubbles of gas are released and rise to the surface.

The bubbles increase in volume as they rise.

Explain this increase in volume. 

A student uses this apparatus to investigate the pressure and volume inside a sealed gas syringe. 

She takes readings of the volume as she increases the pressure (loading) and as she decreases the pressure (unloading).

These are her results. 

The student plots this graph.

The student concludes that her data validates the relationship between pressure and volume of a fixed mass of gas.

Use data from this table to evaluate her conclusion.