The specific heat capacity of a substance is how much energy is needed to raise the temperature of 1kg of that substance by 1°
You can determine the specific heat capacity of substances in the laboratory:
- For a metal, use an electric heater to heat a metal cylinder. Record the temperature with a digital thermometer. Use insulating material to reduce heat loss. Find the energy supplied from = .
- For a liquid, use a heating coil with a digital thermometer. Use insulating material and an insulating lid. Then as above.
Reasons for uncertainties are:
- Heat loss to surroundings – use insulation and a lid; start and end an equal number of degrees above and below room temperature
- False temperature reading due to uneven heat distribution – stir the liquid
- Temperature continues to rise after heater is switched off – measure the highest value
- Thermal capacity of vessel – consider in calculation
The specific latent heat of fusion or vaporisation is the quantity of thermal energy required to change the state of 1kg of substance.
These can be measured in the laboratory:
- Put a heating coil and equal masses of ice in two funnels above beakers 2. Turn on one coil for three minutes. Record the energy transferred.
- Measure the mass of water collected in the beakers. Obtain the mass of water melted due to heating (not the ambient temperature) by subtracting one from the other. Now use .
- There’s a change in internal energy after vaporisation because potential energy increases – work is done in moving molecules apart (however, if the temperature is the same there is no change in KE).