Energy Content of Food - IGCSE Biology Revision Notes

Practical: Energy Content of a Food Sample

We can investigate the energy content of food in a simple calorimetry experiment

Use the measuring cylinder to measure out 25 cm³ of water and pour it into the boiling tube
Record the starting temperature of the water using the thermometer
Record the mass of the food sample
Set fire to the sample of food using the bunsen burner and hold the sample 2 cm from the boiling tube until it has completely burned
Record the final temperature of the water
Repeat the process with different food samples
- E.g. popcorn, nuts, crisps

The energy content of food

Different food samples can be burned in a simple calorimetry experiment to compare the energy contents of the samples

The larger the increase in water temperature, the more energy is stored in the sample
We can calculate the energy in each food sample using the following equation:

$energy transferred per gram of food (J) = \frac{mass of water (g) \times temperature increase (° C) \times 4.2}{mass of food sample (g)}$

4.2 kJ is the specific heat capacity of water, meaning that it is the energy required to raise 1 kg of water by 1 °C
1 cm³ of water has a mass of 1 g

Food sample	Mass of water / g	Mass of food / g	Initial water temperature / °C	Final water temperature / °C	Change in water temperature / °C	Energy transferred per gram of food (J)
Popcorn	25	8.5	20.5	31.2	10.7	132.2
Walnut	25	8.1	20.4	34.1	13.7	177.6

Incomplete burning of the food sample
- Solution: relight the food sample until it no longer lights up
Heat energy is lost to the surroundings
- Solution: whilst heat lost means that the energy calculation is not very accurate, so long as the procedure is carried out in exactly the same way each time (with the same distance between food sample and boiling tube), we can still compare the results