Temperature changes in a system and specific heat capacity — AQA GCSE Physics
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Temperature changes in a system and specific heat capacity explained
Heating a system raises its internal energy, and how far the temperature climbs is set by three things.
Read the full explanation
More energy in gives a bigger rise. More mass gives a smaller rise, because the same energy is shared between more particles. The material matters through its specific heat capacity: 4200 J will raise 1 kg of water by 1 °C but will raise 1 kg of copper (c = 385 J/kg °C) by about 11 °C. Rearranging ΔE = m c Δθ makes this explicit, Δθ = ΔE ÷ (m c), so temperature rise is proportional to energy in and inversely proportional to both mass and specific heat capacity. This is why a reactor wall is built from a material with a very high specific heat capacity: a huge energy transfer then produces only a small temperature rise, keeping the wall below its melting point.
Your focus
- Predict which of two equal masses of different materials reaches the higher temperature when both are given 10 kJ, using their specific heat capacities.
- Explain why a reactor wall or a storage heater is built from a material with a high specific heat capacity, in terms of the temperature rise produced by a large energy transfer.
- Compare the temperature rise of 1 kg and 2 kg of water supplied with the same energy, and justify the difference.
Temperature changes in a system and specific heat capacity exam tips
Marking Points
- one mark for stating that a larger energy input produces a larger temperature rise when mass and material are unchanged
- one mark for stating that a larger mass of the same substance gives a smaller temperature rise for the same energy input
- one mark for naming the property of the material as its specific heat capacity
- one mark for linking a high specific heat capacity to a small temperature increase for a large energy transfer, for example a reactor wall that does not reach its melting point
Examiner Tips
- 💡When a question says which factors affect the temperature rise, name all three: energy transferred, mass, and the material's specific heat capacity.
- 💡If a question asks why a material was chosen, answer in terms of the size of the temperature change it produces, not just in terms of the value of c.
- 💡Hold the other factors constant in your answer; examiners look for comparisons of the same mass or the same energy input.
Common Mistakes
- claiming a larger mass reaches a higher temperature for the same energy supplied
- using the words temperature and thermal energy as though they mean the same thing
- assuming two equal masses given the same energy always end at the same temperature, whatever the material
- treating specific heat capacity as a measure of how hot a substance can get rather than how much energy each degree costs