Changes of state

A piece of steel is heated until it has all melted.

Calculate the change in thermal energy when the temperature of the piece of steel is increased by 50 °C.

mass of steel = 4.0 kg

specific heat capacity of steel = 420 J/kg °C

Use the equation:

change in thermal energy = mass × specific heat capacity × temperature change

The internal energy of the steel increases as the steel is heated.

What is meant by ‘internal energy of the steel’?

Tick (✓) one box.

Solid steel cannot be poured.

Which statement about the particles in a solid gives the reason why?

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Complete the sentence.

Choose the answer from the box.

Which diagram shows how the arrangement of particles changes when a solid melts and becomes a liquid?

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The density of steel decreases as it melts.

How does the spacing of the particles change as the steel melts?

Complete the sentence.

Choose the answer from the box.

Steel is a mixture of iron and a small amount of carbon.

Table 1 shows the mass of carbon in 1.0 kg of different types of steel.

A 4.0 kg piece of steel contains 18 grams of carbon.

Determine which type of steel the 4.0 kg piece is made from.

You should include a calculation in your answer.

The 4.0 kg piece of solid steel was heated until it reached its melting point.

The additional energy required to melt the piece of steel was 280 000 J.

Calculate the specific latent heat of fusion of the steel.

Use the Physics Equations Sheet.

A student made measurements to determine the specific heat capacity of vegetable oil.

Figure 10 shows the equipment used.

Describe how the student could use the equipment shown in Figure 10 to determine the specific heat capacity of vegetable oil.

Give one risk when using the equipment in Figure 10.

A different student did not have a joulemeter and calculated the energy transferred by the electric heater.

Use the Physics Equations Sheet to answer questions 06.3 and 06.4.

Write down the equation linking energy transferred (E), power (P) and time (t).

The electric heater had a power output of 50 watts.

Calculate the time taken for the electric element to transfer 4750 joules of energy to the vegetable oil.

In a deep fryer, vegetable oil is heated by an electric heating element. Food is then cooked in the hot vegetable oil.

The deep fryer contains an electrical component to monitor the temperature of the vegetable oil.

Figure 11 shows how the resistance of this electrical component changes with temperature.

What electrical component is used to monitor the temperature of the vegetable oil?

The electric heating element in the deep fryer automatically switches off when the vegetable oil reaches a certain temperature.

Figure 12 shows how the temperature of the vegetable oil changed after the deep fryer was switched on.

Determine the resistance of the electrical component when the electric heating element automatically switched off.

Use Figure 11 and Figure 12.

Some chips were put in the deep fryer.

In the deep fryer, water in the chips underwent a physical change and became steam.

Why is this a physical change?

Tick (✓) one box.

A student made measurements to determine the specific heat capacity of vegetable oil. Figure 2 shows the equipment used.

Describe how the student could use the equipment shown in Figure 2 to determine the specific heat capacity of vegetable oil.

Give one risk when using the equipment in Figure 2.

A different student did not have a joulemeter and calculated the energy transferred by the electric heater.

Use the Physics Equations Sheet to answer questions 02.3 and 02.4.

Write down the equation linking energy transferred (E), power (P) and time (t).

The electric heater had a power output of 50 watts. Calculate the time taken for the electric element to transfer 4750 joules of energy to the vegetable oil.

In a deep fryer, vegetable oil is heated by an electric heating element. Food is then cooked in the hot vegetable oil. The deep fryer contains an electrical component to monitor the temperature of the vegetable oil. Figure 3 shows how the resistance of this electrical component changes with temperature.

What electrical component is used to monitor the temperature of the vegetable oil?

The electric heating element in the deep fryer automatically switches off when the vegetable oil reaches a certain temperature. Figure 4 shows how the temperature of the vegetable oil changed after the deep fryer was switched on.

Determine the resistance of the electrical component when the electric heating element automatically switched off. Use Figure 3 and Figure 4.

Some chips were put in the deep fryer. In the deep fryer, water in the chips underwent a physical change and became steam. Why is this a physical change? Tick (✓) one box.

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 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.