AQA · GCSE · Combined Science · Higher

Coolant temperature and internal energy

Q06.1 2 marks

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.

Diagram of an air source heat pump. A pipe containing coolant passes through an evaporator outside the building, a compressor, a condenser inside the building, and a decompressor. Labels indicate air outside building, air inside building, evaporator, pipe, coolant, compressor, decompressor and condenser. — Figure 13

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

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Marking points

1 Say that the particles gain kinetic energy, or that the particles move faster.
2 Say that the particles gain potential energy as the coolant evaporates.
3 Conclude that the internal energy increases, because internal energy is the total kinetic and potential energy of the particles.

Full-mark answer

As the temperature increases, the particles of the coolant gain kinetic energy and potential energy. The internal energy increases because it is the sum of the kinetic and potential energy of the particles.

Why this answer loses marks

The internal energy stays the same because the coolant changes state.

Energy is transferred to the coolant, increasing the kinetic and potential energy of its particles, so internal energy increases.

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