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14 kJ/g. By trial, the energy per unit mass values (measured in units of kJ/g) are: 15.2; 14.7; 14.8; 13.9; 12.9; 13.7.

  • 7.

    The basic building blocks of your proteins come from the proteins of the foods you eat. If you eat only carbohydrates your body will be unable to make some essential materials. A balanced diet is important to your health.

  • 8.

    Bacon is meat – it contains proteins and lipids. Bread is made from grains which contain carbohydrates, and the butter is almost pure lipid.

  • 9.

    The food we eat can affect our health in the long term. A single “unhealthy” meal is not a concern, but nutri- tionists recommend that people maintain a balanced diet in which most food energy comes from carbohy- drates and the least comes from fats.

10. Soaps are made by heating fats or oils with sodium hydroxide (lye). One part of the soap molecule is soluble in fat and another part is soluble in water. This allows soap to lift off greasy dirt.

= 18 J of light energy is emitted = 2.3 102 J 11. Eoutput 12. Einput

13. Much of the energy lost during the experiment would be transferred to the air surrounding the burning walnut. To improve the transfer of energy from the hot air to the water the students could have enclosed the entire apparatus in a container which kept the warm air in contact with the test tube for a longer period of time.

Certainly many other approaches are possible.

  • 14.

    a. Answers will vary.

    • b.

      If your insulation worked well the energy loss of the insulated can will have been much smaller than that lost by the uninsulated can.

    • c.

      Repeat the procedures this time using three cans, one which is not insulated, one with a single thick layer of insulation, and one with a number of thinner layers of insulation. You should ensure both insu- lated cans have the same total thickness of insulation.


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