Specified practical - Determination of specific heat capacity

There are different ways to investigate the specific heat capacity of a material. In this specified practical activity, it is important to:

  • record the time accurately
  • measure and observe the change in temperature and then calculate the energy transferred
  • use appropriate apparatus and methods to determine the specific heat capacity of a sample of material

Aim of the experiment

To determine the specific heat capacity of a metal block.

A 50 watt immersion heater is connected to a power supply and placed on a 1kg metal block. A thermometer is next to the heater.

Method

  1. Ensure the power supply is switched off.
  2. Place the immersion heater into the central hole at the top of the block.
  3. Place the thermometer into the smaller hole and put a couple of drops of oil into the hole to make sure the thermometer is surrounded by a good conducting material.
  4. Fully insulate the block by wrapping it loosely with cotton wool.
  5. Record the temperature of the block.
  6. Connect the heater to the power supply and turn it on for ten minutes.
  7. Record the temperature of the metal block every minute.
  8. After ten minutes the temperature will still rise even though the heater has been turned off and then it will begin to cool. Record the highest temperature that it reaches and calculate the temperature rise during the experiment.

Results

Record results in a suitable table. The example below shows some suitable results for an aluminium block.

Time (mins)Temperature (°C)
015
117
219
321
423
525
628
731
834
937
1040
Highest reading44

Analysis

The block has a mass of 1 kg and the heater was running for 10 minutes = 600 seconds.

Using the example results:

energy transferred = power × time

\ E = Pt \

\ E = 50 \times 600 \

\ E = 30,000 \ J \ (\Delta Q) \

\ \Delta Q = mc \Delta \theta

\ c = \frac{\Delta Q}{m \Delta \theta}

\ c = \frac{30,000}{1 \times (44 - 15)}

\ c = 1,034 \ J/kg \textdegree C

The actual value for the specific heat capacity of aluminium is 900 J/kg°C. The calculated value does not match exactly but it is in the correct order of magnitude.

Evaluation

  • All experiments are subject to some amount of experimental error due to inaccurate measurement, or variables that cannot be controlled. In this case, not all of the heat from the immersion heater will be heating up the aluminium block, some will be lost to the surroundings.
  • More energy has been transferred than is needed for the block alone, as some is transferred to the surroundings. This causes the calculated specific heat capacity to be higher than for one kilogram (kg) of aluminium alone.

Risk assessment

HazardConsequenceControl measures
Hot immersion heater and metal blockBurn skinDo not switch on the heater before it is placed in the block. Do not touch when switched on. Allow time to cool before packing away equipment. Run any burn under cold running water for at least 10 minutes.
Move on to Video
next