Energy
Specific Heat Capacity
AQA GCSE Physics
Equation and units
change in thermal energy = mass × specific heat capacity × temperature change
ΔE = m c Δθ
| Quantity | Symbol | Unit |
|---|---|---|
| change in thermal energy | ΔE | J |
| mass | m | kg |
| specific heat capacity | c | J/kg °C |
| temperature change | Δθ | °C |
- Rearranged: c = ΔE / (m Δθ), m = ΔE / (c Δθ), Δθ = ΔE / (m c).
- Temperature change = final temperature − initial temperature.
What the temperature rise depends on
- Specific heat capacity is the energy needed to raise the temperature of 1 kg of a substance by 1 °C.
- The temperature rise depends on the mass of the substance, the material it is made of and the energy supplied.
- A substance with a lower specific heat capacity has a steeper temperature-time gradient: less energy is needed to increase the temperature by a fixed amount.
Required practical 1: specific heat capacity
Required practical 1: specific heat capacity of water
- Measure the mass of the empty beaker on the balance.
- Fill the beaker with water and measure the total mass of beaker and water.
- Mass of water = total mass − mass of beaker.
- Put the heater and the thermometer in the water. Insulate the beaker of water with a lid.
- Turn the power supply on so the heater increases the temperature of the water.
- Measure the temperature change with the thermometer.
- Use a joulemeter to measure the energy transferred to the water.
- Calculate the specific heat capacity using ΔE = m c Δθ.
- Calculate the percentage difference from the accepted value: divide the difference by the accepted value, then multiply by 100.
- Control variable: the initial temperature.
- Insulating the beaker reduces energy transfer to the surroundings, so the calculated specific heat capacity is more accurate.
- Hazards: hot water and the heater, which can scald the skin.
Using a metal block
- The thermometer sits in a hole in the block so the thermometer temperature was the same as the temperature of the iron block.
- Insulating the block: the iron block will transfer thermal energy to the surroundings at a lower rate, so the calculated specific heat capacity will be more accurate.
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