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.
E=mL
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).