AQA GCSE Physics
AQA GCSE Physics 4.3.2.3 Changes of Heat and Specific Latent Heat Exam Questions
Free AQA GCSE Physics exam questions for 4.3.2.3 Changes of Heat and Specific Latent Heat, with a mark scheme for every pack. Covers specific latent heat of fusion and vaporisation, energy for changes of state, E = mL, and heating and cooling graphs.
4.3.2.3 Changes of Heat and Specific Latent Heat exam questions
2 question packs 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 AQA GCSE Physics 4.3.2.3 Changes of Heat and Specific Latent Heat
This AQA GCSE Physics section covers the energy needed to change the state of a substance without changing its temperature. You need the meaning of specific latent heat, the difference between latent heat of fusion and of vaporisation, the equation E = m L, and how to interpret heating and cooling graphs with flat sections. It is examined on Paper 1 and follows directly from internal energy and specific heat capacity. Examiners frequently combine m c Δθ and m L in one multi-step question, so know which equation applies to each stage.
What you need to know
- Latent heat If a change of state happens, the energy supplied changes the internal energy (the potential energy of the particles) but not the temperature. The energy needed for a substance to change state is called latent heat.
- Specific latent heat The specific latent heat of a substance is the amount of energy required to change the state of one kilogram of the substance with no change in temperature.
- The equation E = m L, where E is energy for a change of state in J, m is mass in kg and L is specific latent heat in J/kg. Given on the equation sheet.
- Fusion and vaporisation Specific latent heat of fusion: change of state from solid to liquid. Specific latent heat of vaporisation: change of state from liquid to vapour. For water, vaporisation needs far more energy than fusion.
- Heating and cooling graphs On a temperature against time graph, sloping sections show temperature changes within one state and flat sections show changes of state. The flat section at the higher temperature is boiling; the lower one is melting.
- Energy released The same amount of energy is released when a substance condenses or freezes as was absorbed when it boiled or melted.
Common mistakes in 4.3.2.3 Changes of Heat and Specific Latent Heat
- Thinking temperature rises during melting. On the graph, the flat section shows constant temperature while the state changes.
- Mixing up fusion (melting) and vaporisation (boiling).
- Using E = m L for the whole of a heating process. Use m c Δθ for temperature changes and m L only for changes of state, then add the stages.
- Forgetting to convert grams to kilograms when L is in J/kg.
Try three 4.3.2.3 Changes of Heat and Specific Latent Heat exam-style questions
1. Calculate the energy needed to melt 0.25 kg of ice at 0 °C. Specific latent heat of fusion of ice = 334 000 J/kg. (2 marks)
Show the mark scheme answer
E = m L = 0.25 x 334 000; = 83 500 J.
2. Describe what is happening to the particles during the flat section of a heating graph for water at 100 °C. (2 marks)
Show the mark scheme answer
Energy supplied increases the potential energy of the particles (internal energy increases); breaking bonds or overcoming forces between particles as the water boils, with no increase in kinetic energy so temperature stays constant.
3. 0.10 kg of water at 100 °C is turned completely into steam. Specific latent heat of vaporisation of water = 2 260 000 J/kg. A kettle element supplies energy at 2000 W. Calculate the minimum time taken. (3 marks)
Show the mark scheme answer
E = 0.10 x 2 260 000 = 226 000 J; t = E / P = 226 000 / 2000; = 113 s.
4.3.2.3 Changes of Heat and Specific Latent Heat FAQs
What does AQA GCSE Physics 4.3.2.3 Changes of heat and specific latent heat cover?
It covers latent heat, specific latent heat of fusion and vaporisation, the equation E = m L and interpreting heating and cooling graphs.
Which paper is specific latent heat examined in?
It is part of the Particle Model of Matter topic on AQA GCSE Physics Paper 1.
How do I tackle multi-stage heating questions?
Split the process into stages: use m c Δθ for each temperature change and m L for each change of state, then add the energies together.
