OCR GCSE Physics A (Gateway)
OCR GCSE Physics A P1.2 Changes of State Exam Questions
Free OCR GCSE Physics A exam questions for P1.2 Changes of State, with a mark scheme for every pack. Covers internal energy, changes of state, specific heat capacity, specific latent heat, heating and cooling curves and conservation of mass.
P1.2 Changes of State exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About OCR GCSE Physics A P1.2 Changes of State
P1.2 continues the P1 Matter chapter by explaining what happens to particles when a substance is heated or changes state. You learn that heating increases internal energy, which either raises the temperature or changes the state. You calculate energy using specific heat capacity and specific latent heat, interpret heating and cooling curves, and describe how to measure specific heat capacity in practical work. Changes of state are physical changes that conserve mass and are reversible. The topic builds on P1.1 and links to P7 on energy. Examiners commonly ask you to explain the flat sections of a heating curve and to complete multi-step energy calculations.
What you need to know
- Internal energy The total energy stored by particles, made of kinetic energy (movement) and potential energy (due to their positions and bonds). Heating increases internal energy.
- Changes of state Melting, freezing, boiling, evaporating, condensing and sublimating. These are physical changes: mass is conserved and the material recovers its original properties if the change is reversed.
- Specific heat capacity Change in internal energy = mass x specific heat capacity x change in temperature. It is the energy needed to raise the temperature of 1 kg of a substance by 1 degree Celsius.
- Specific latent heat Thermal energy for a change of state = mass x specific latent heat. Latent heat of fusion is for melting; latent heat of vaporisation is for boiling.
- Heating and cooling curves The flat parts show changes of state. Energy is used to break bonds between particles (or released when bonds form), so temperature stays constant.
- Practical Measure specific heat capacity using an electrical heater, a joulemeter or ammeter and voltmeter, a thermometer and an insulated block. Insulating the block reduces energy losses.
Common mistakes in P1.2 Changes of State
- Saying temperature rises during boiling. It stays constant at the boiling point.
- Confusing temperature with internal energy. Temperature relates to average kinetic energy of particles, not their total energy.
- Saying changes of state are chemical changes. They are physical and reversible.
- Using specific heat capacity for a change of state. Use specific latent heat when there is no temperature change.
- Forgetting that energy lost to the surroundings makes measured specific heat capacity too high.
Try three P1.2 Changes of State exam-style questions
1. Calculate the energy needed to raise the temperature of a 2.0 kg aluminium block by 25 degrees Celsius. Specific heat capacity of aluminium = 900 J/kg degrees Celsius. (2 marks)
Show the mark scheme answer
Energy = m x c x change in temperature = 2.0 x 900 x 25; = 45 000 J.
2. Calculate the energy needed to melt 0.40 kg of ice at 0 degrees Celsius. Specific latent heat of fusion of ice = 334 000 J/kg. (2 marks)
Show the mark scheme answer
Energy = m x L = 0.40 x 334 000; = 133 600 J.
3. Explain why the temperature of water stays at 100 degrees Celsius while it boils. (2 marks)
Show the mark scheme answer
The energy supplied is used to break the bonds between particles (increasing potential energy); not to increase their kinetic energy, so temperature does not rise.
P1.2 Changes of State FAQs
What does OCR GCSE Physics A (Gateway Science) P1.2 Changes of State cover?
It covers internal energy, changes of state, specific heat capacity, specific latent heat and heating and cooling curves.
Which paper is P1.2 examined on?
Topics P1 to P4 are assessed on Paper 1 (Foundation) or Paper 3 (Higher), alongside practical skills.
What equations do I need for Changes of State?
You need change in internal energy = mass x specific heat capacity x change in temperature, and thermal energy for a change of state = mass x specific latent heat.
