Particle motion and pressure in gases

Data-storage computers get very hot.

Scientists investigated using the sea to cool data-storage computers.

The computers were set up inside a large metal container.

Figure 8 shows the metal container before it was lowered into the sea.

Why is the container made of metal?

Tick (✓) one box.

The walls of the container are solid.

Figure 9 shows an arrangement of six particles in a solid.

The air inside the container is a gas.

Draw an arrangement of six particles in a gas in the box below.

How does the air in the container exert pressure on the container?

Tick (✓) one box.

As the container is lowered into the sea, the temperature of the air in the container decreases.

Complete the sentence.

Choose the answer from the box.

When the temperature of the air in the container decreases, the average speed of the

After the temperature of the air in the container had decreased, the computers were switched on.

The computers caused the temperature of the air to then increase.

Describe how the air pressure in the container changed as the temperature decreased and then increased.

The container has a length of 12 m.

The container has a cross-sectional area of 7.5 m².

Calculate the volume of the container.

Use the equation:

volume = length × cross-sectional area

Use the Physics Equations Sheet to answer questions 05.7 and 05.8.

Write down the equation that links density (ρ), mass (m) and volume (V).

The average density of the container and its contents is 1100 kg/m³.

Calculate the mass of the container and its contents.

Use your answer to Question 05.6

Energy can be stored using a Compressed Air Energy Storage (CAES) system.

When more electricity is generated than is needed, a CAES system uses the surplus electricity to compress air in a storage tank.

When there is a greater demand for electricity, the CAES system releases the compressed air to generate electricity.

Figure 7 shows a diagram of the CAES system.

The CAES system has two processes:

• compressing air to store energy. This process has an efficiency of 0.72

• releasing the air to generate electricity. This process has an efficiency of 0.86

Calculate the efficiency of the CAES system.

Give your answer to 2 significant figures.

The generator works when forces from the compressed air cause a turbine to rotate.

When particles of air collide with the turbine they transfer energy to the turbine.

In warm weather the temperature of the compressed air increases, increasing the pressure inside the storage tank.

Explain how the motion of the particles in warmer air causes an increase in the power transferred to the turbine.

The volume of the storage tank is 5.0 × 10⁵ m³.

The density of the compressed air is 48 kg/m³.

specific heat capacity of air = 1100 J/kg °C

The temperature of the compressed air increases from 12 °C to 27 °C.

Calculate the energy transferred to the compressed air in the storage tank.

Use the Physics Equations Sheet.

Give your answer in standard form.

The UK government wants the amount of carbon dioxide released into the atmosphere to be reduced.

Explain why efficient energy storage is important in reducing the amount of carbon dioxide released when generating electricity.

Figure 12 shows a device that uses a mug of hot coffee to turn a wheel.

The hot coffee increases the temperature of the air in the chamber. Explain how the pressure in the chamber changes.

For the device to work, the air in the chamber must increase in temperature quickly. Explain why the bottom of the air chamber is made of metal rather than plastic.

The mass of air in the chamber is constant. What property of air allows a small change in internal energy to cause a large temperature change to the air in the chamber?

The changes in pressure in the air chamber cause the wheel to turn. Suggest one way to increase the speed at which the wheel turns.

The temperature of the coffee decreases as the device is used. The initial temperature of the coffee was 76 °C. The internal energy of the coffee decreased by 15 kJ.

specific heat capacity of coffee = 4200 J/kg °C Calculate the final temperature of the coffee. Use the Physics Equations Sheet.

A student investigated how the pressure of a gas depends on its temperature. The volume of the gas did not change. Figure 6 shows the equipment used.

Pressure is sometimes measured in units called atmospheres.

What is 1 atmosphere in kilopascals (kPa)?

The student took four pressure readings for each temperature. Table 1 shows the pressure readings when the temperature was 50.0 °C

Calculate the uncertainty in the mean pressure.

Figure 7 shows a sketch graph of the results.

The student said that as the temperature increases the pressure increases. Give a better description of the relationship between temperature and pressure.

A pressure cooker is a sealed pot that uses steam to cook food. Figure 8 shows a pressure cooker.

When the water in the pressure cooker starts to boil:

• the amount of steam in the pressure cooker increases

• the temperature of the steam increases above 100 °C

Explain why these changes make the pressure in the cooker increase.

If the pressure inside the pressure cooker becomes greater than 200 kPa then some of the steam is released through the safety valve. The released steam expands as it moves into the atmosphere. Explain how a change in density of the steam is caused by a change in the arrangement of particles in the steam as it is released.

An air source heat pump transfers energy from the air outside a building to increase the temperature of the air inside the building. Figure 13 shows an air source heat pump.

The compressor is connected to the mains electricity supply. The pipe in the heat pump contains a substance called coolant. In the evaporator, energy is transferred from the air outside the building to the liquid coolant. The temperature of the coolant increases and it evaporates.

Explain what happens to the internal energy of the coolant as its temperature increases.

What name is given to the energy needed to change the state of the liquid coolant?

What happens to the mass of the coolant as it evaporates and becomes a vapour? Tick (✓) one box.

The compressor increases the density and temperature of the coolant vapour inside the pipe. Explain why the pressure in the pipe increases.

The condenser transfers energy from the coolant to the air in the building. When the total energy input to the heat pump system is 1560 kJ the temperature of the air in the building increases from 11.6 °C to 22.1 °C. The efficiency of the heat pump system is 87.5%. The mass of the air inside the building is 125 kg. Calculate the specific heat capacity of the air in the building. Give your answer in standard form.

The air in the building gains 400 J for every 100 J of energy transferred from the mains electricity supply to the compressor. An advertisement claims that the heat pump system has an efficiency of 400%. Explain why the advertisement is not correct.

A scientist had a balloon which was filled with air.

Which statement describes how air particles move? Tick (✓) one box.

The temperature of the air was 19 °C The scientist dipped the balloon into liquid nitrogen. The temperature of the liquid nitrogen was −196 °C

Which thermometer could be used to measure the temperature of the liquid nitrogen? Tick (✓) one box.

The scientist wore special insulating gloves when putting the balloon into the liquid nitrogen. Suggest why.

When the balloon was put into liquid nitrogen the temperature of the air in the balloon decreased. Complete the sentences. Choose answers from the box. Each answer may be used once, more than once or not at all.

As the air in the balloon cooled down, the speed of the particles

The air in the balloon had a mass of 0.00320 kg The temperature of the air in the balloon decreased by 215 °C The change in thermal energy of the air in the balloon was 860 J Calculate the specific heat capacity of the air in the balloon. Use the Physics Equations Sheet.

The liquid nitrogen boiled. What happens to the temperature of nitrogen as it boils?

Tick (✓) one box.

The scientist recorded measurements to calculate the specific latent heat of vaporisation of nitrogen.

What is meant by vaporisation? Tick (✓) one box.

The mass of nitrogen that vaporised was 0.0072 kg 1440 J of energy was transferred to the nitrogen as it vaporised. Calculate the specific latent heat of vaporisation of nitrogen. Use the Physics Equations Sheet.

A scientist cooled the air inside a container.

The temperature of the air changed from 20 °C to 0 °C

The volume of the container of air stayed the same.

Explain how the motion of the air molecules caused the pressure in the container to change as the temperature decreased.

The air contained water that froze at 0 ° C

The change in internal energy of the water as it froze was 0.70 kJ

The specific latent heat of fusion of water is 330 kJ/kg

Calculate the mass of ice produced.

Use the Physics Equations Sheet.

The air also contained oxygen, nitrogen and carbon dioxide.

Oxygen boils at –183 °C and freezes at –218 °C Nitrogen boils at –195 °C and freezes at –210 °C Carbon dioxide sublimates at –78 °C

The scientist continued to cool the air to a temperature of –190 °C

What is the state of each substance at –190 °C?

Tick (✓) one box for each row of the table.

The air also contained a small amount of argon.

As the temperature of the air decreased from 20 °C to –190 °C the argon changed from a gas to a liquid to a solid.

Explain the changes in the arrangement and movement of the particles of the argon as the temperature of the air decreased.

A scientist cooled the air inside a container.

The temperature of the air changed from 20 °C to 0 °C The volume of the container of air stayed the same. Explain how the motion of the air molecules caused the pressure in the container to change as the temperature decreased.

The air contained water that froze at 0 ° C The change in internal energy of the water as it froze was 0.70 kJ The specific latent heat of fusion of water is 330 kJ/kg Calculate the mass of ice produced. Use the Physics Equations Sheet.

The air also contained oxygen, nitrogen and carbon dioxide. Oxygen boils at –183 °C and freezes at –218 °C Nitrogen boils at –195 °C and freezes at –210 °C Carbon dioxide sublimates at –78 °C The scientist continued to cool the air to a temperature of –190 °C

What is the state of each substance at –190 °C?

Tick (✓) one box for each row of the table.

The air also contained a small amount of argon. As the temperature of the air decreased from 20 °C to –190 °C the argon changed from a gas to a liquid to a solid. Explain the changes in the arrangement and movement of the particles of the argon as the temperature of the air decreased.

Figure 5 shows a diver. The diver is using a canister of compressed air so that he can breathe underwater.

Which two sentences describe the movement of the air particles in the canister? Tick two boxes.

The temperature of the air inside the canister increases. What happens to the movement of the air particles?

It could be dangerous if the temperature of the air inside the canister increased by a large amount. Explain why.

A canister of air was tested to find out how the pressure changed when it was used by a diver.

• Air was allowed to escape from the canister.

• The pressure of the air in the canister was recorded every 5 minutes for 80 minutes.

Figure 6 shows the results.

Estimate the atmospheric pressure. Use Figure 6

Divers can safely stay underwater until the pressure of the air in the canister has reduced to 25% of its original value. Determine the maximum time the diver can safely stay underwater. Use Figure 6

What happens to the volume of the air when it is released from the canister?