Ideal Gases (Edexcel IGCSE Physics (Modular): Unit 2)

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.

(i) Convert a temperature of 27 °C into kelvin (K).

(1)

temperature = ............................. K

(ii) The gas in a cylinder has a pressure of 210 kPa at a temperature of 27°C. Calculate the new pressure when the temperature of the gas rises to 81°C.

(3)

pressure = ............................ kPa

Aneroid barometers are used to measure air pressure.

A student makes a model aneroid barometer as shown. 

(i) The balloon fabric is attached to the can to stop the air escaping.

Explain how the air inside the can causes a pressure on the balloon fabric.

(3)

(ii) The balloon fabric is tight and flat.

The pointer is horizontal as shown.

Explain what happens to the different parts of the model when the atmospheric pressure increases. [You may assume that the temperature remains constant.] 

(4)

 (ii) Suggest two ways that the model could be altered to increase its sensitivity to changes in atmospheric pressure.

(2)

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

(i) State how this affects the reading shown by the pointer. 

(1)

(ii) Explain why this happens.

(2)

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. 

(i) How would increasing the temperature of the compressed air affect the pressure in the can? 

(1)

(ii) Explain your answer. 

(2)

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. 

volume = ..................................... cm³

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. 

 (i) Draw a graph to show how the volume of gas varies with temperature. 

(3)

(ii) Circle the anomalous point on your graph. 

(1)

 (iii) Use your graph to find the temperature of the gas when its volume is zero. 

(1)

Temperature = ..................................... °C

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. 

 (i) State the equation linking density, mass and volume.

(1)

(ii) Calculate the mass of hot air in the balloon. 

(3)

 Mass of hot air = .......................... kg

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

(i) Suggest a reason for this change in the outside air pressure. 

(1)

(ii) Suggest how the decrease in air pressure outside the balloon affects the hot air inside. 

(1)

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. 

(i) How do the gas particles produce a pressure on the walls of the spray-can?

(3)

(ii) A student presses the button and some liquid leaves the can. 

The student concludes

Evaluate this conclusion.

(3)

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. 

 pressure = ..................................... kPa

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. 

(i) Suggest how this affects the pressure of the gas in the space above the cream. 

(2)

(ii) When the tap is opened, the pressure of the gas forces the cream out of the spout.

The pressure outside the can is less than it is inside.

Suggest what happens to the dissolved gas as the cream leaves the can. 

(1)

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. 

(i) The cylinder contains 8 litres of air at 200 times atmospheric pressure.

The air is released from the cylinder at normal atmospheric pressure.

The diver needs 16 litres of air per minute.

Calculate the maximum amount of time that the diver can breathe under water using this cylinder. 

(4)

 time = ..................................... minutes

(ii) When the diver breathes out, bubbles are released.

Suggest why the bubbles expand as they rise to the surface.

(2)

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

(i) Suggest how the student could measure the volume of an inflated balloon.

(2)

(ii) The student plans to measure the pressure of the air in the balloon. 

Explain why the student’s plan will not work. 

(2)

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.  

 pressure = .......................... kPa

(i) State the equation linking pressure difference, depth, density and g. 

(1)

(ii) Calculate the increase in pressure when the diver descends from the surface to a depth of 11 m.

(2)

increase in pressure = .......................... kPa

(iii) Calculate the total pressure on the diver at a depth of 11 m.

Assume that the atmospheric pressure remains at 101 kPa. 

(1)

total pressure = .......................... 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. 

(i) Complete the table by filling in the missing value. 

(1)

(ii) Suggest why the student takes readings for increasing the pressure and for decreasing the pressure.

(2)

The student plots this graph.

(i) Suggest a reason why the axes do not start from the origin (0,0). 

(1)

(ii) The student has drawn both a straight line of best fit and a curve of best fit.

Discuss which line is correct for this investigation.

(2)

(iii) Suggest a way that the student could make this experiment valid (a fair test).

(1)

 (iv) Suggest two ways in which the student could improve the quality of her data.

(2)

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.