Wednesday, 4 January 2012

2.32 Energy Content of Food

Recall how to carry out a simple experiment to determine the energy content in a food sample.

Apparatus:

  • Thermometer
  • Boiling Tube filled with 20 cm3 Water
  • 10 cm3 of food sample in Crucible

Method:

  1. Measure the initial temperature of the water (degree centigrade)
  2. Ignited the food source
  3. Heat the water with the ignited food
  4. Measure the final temperature of the water (degree centigrade)
Calculation:
Let's say our initial temperature was 20 degrees Celsius and the final temperature was 30 degrees Celsius
1 cm3 of water has a weight of 1g and in order to increase one degrees it would take 4 joules

Energy released from food per gram (J) = (mass of water (g)*temperature rise (degree centigrade)*4.2)/Mass of food sample (g)

In our case:
Energy released from food per gram (J)= (20g*(30-20)*4.2)/10
=84 J/g
So in our food there were 84 joules per gram

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