State — 2 marks
A student heats water in a kettle. The heating element transfers energy to the water, causing its temperature to increase from 20°C to 100°C.
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(a) State what is meant by internal energy.
[1 mark]
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(b) State how the internal energy of the water changes as it is heated from 20°C to 100°C.
[1 mark]
Show mark scheme
- (a) Internal energy is the total (random/kinetic and potential) energy of all the particles/atoms/molecules in an object/substance. (Accept: the sum of all kinetic and potential energy of particles)
- (b) The internal energy increases / increases because the particles gain kinetic energy and move faster / particles have greater kinetic energy
Explain — 4 marks
A student heats water in a metal kettle on a cooker. The water temperature increases from 20°C to 100°C. The metal handle of the kettle also becomes hot, even though it is not in direct contact with the heat source.
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(a) Explain what happens to the internal energy of the water as it is heated from 20°C to 100°C.
[1 mark]
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(b) Explain why the metal handle of the kettle becomes hot, even though it is not in direct contact with the heat source.
[2 marks]
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(c) The kettle is left on the cooker after the water reaches 100°C. Explain why the temperature of the water does not increase further, even though energy is still being transferred to it.
[1 mark]
Show mark scheme
- (a) The internal energy of the water increases / increases due to increased kinetic energy of particles (or equivalent statement about movement/vibration of water molecules)
- (b) Heat/thermal energy is conducted through the metal of the kettle from the base to the handle
- (b) In metals, vibrating particles transfer kinetic energy to neighbouring particles (or equivalent explanation of conduction mechanism involving particle movement/vibration)
- (c) The energy transferred is used to change the state of water from liquid to gas / energy goes into evaporation, not increasing temperature
Explain — 3 marks
A student heats water in a kettle. The water temperature increases from 20°C to 100°C. During heating, some thermal energy is also transferred to the metal kettle itself, causing it to become hot to touch.
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(a) Explain what happens to the internal energy of the water as it is heated in the kettle.
[1 mark]
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(b) The metal kettle becomes hot even though it is not in direct contact with the heating element. Explain how thermal energy is transferred through the metal kettle.
[1 mark]
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(c) Explain why the internal energy of both the water and the kettle increases, even though the same amount of electrical energy is supplied to the system.
[1 mark]
Show mark scheme
- (a) The internal energy of the water increases (1 mark) - accept: 'the kinetic energy of particles increases' or 'particles move faster/have more movement'
- (b) Thermal energy is transferred by conduction (1 mark) - accept: 'heat is conducted through the metal' or 'vibrating particles transfer energy to neighbouring particles'
- (c) The electrical energy supplied is shared/distributed between both the water and the kettle (1 mark) - accept: 'energy is transferred to both objects' or 'not all energy goes into heating the water alone'
Define — 3 marks
A student is investigating energy transfer in a cup of hot chocolate. When the drink is first poured at 80°C, the cup feels warm to touch. Over time, the temperature decreases as the drink cools to room temperature. The student notices that the cup and the drink eventually reach the same temperature.
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(a) Define internal energy.
[1 mark]
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(b) Define thermal energy transfer.
[1 mark]
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(c) Explain why the internal energy of the hot chocolate decreases as it cools to room temperature.
[1 mark]
Show mark scheme
- (a) Internal energy is the total kinetic and potential energy of all the particles/atoms/molecules in an object
- (b) Thermal energy transfer is the movement/flow of energy from a region of higher temperature to a region of lower temperature
- (c) Thermal energy is transferred from the hot chocolate to the surroundings (cup and air) because the drink is at a higher temperature, so the internal energy decreases as energy leaves the system
Calculate — 3 marks
A student heats 0.5 kg of water in a kettle from 20°C to 100°C. The specific heat capacity of water is 4200 J/(kg·°C). After reaching 100°C, the student continues heating and some of the water evaporates. The specific latent heat of vaporisation of water is 2.26 × 10⁶ J/kg.
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(a) Calculate the energy transferred to the water to raise its temperature from 20°C to 100°C.
[1 mark]
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(b) The student then heats the water at 100°C until 0.15 kg has evaporated. Calculate the total energy transferred during both the heating and evaporation stages.
[2 marks]
Show mark scheme
- (a) Correct substitution into Q = mcΔT with m = 0.5, c = 4200, ΔT = 80, giving Q = 168,000 J (or 1.68 × 10⁵ J)
- (b) Correct calculation of energy for evaporation using Q = mL with m = 0.15 and L = 2.26 × 10⁶, giving Q = 339,000 J (or 3.39 × 10⁵ J)
- (b) Correct addition of both energy values: 168,000 + 339,000 = 507,000 J (or 5.07 × 10⁵ J)
GCSE Perfect