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Calories: Biochemical Energy

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Author: Janice VanCleave

Food is a requirement for life. It is the body's fuel and is necessary for the production of the energy needed for daily activities and body maintenance.

In this project, you will experimentally determine the amount of heat energy released by different foods. You will use a simplified calorimeter, an instrument that measures the energy released when food burns, to determine food Calories (note the capital C). You will also look at the difference between gram calories and food Calories and compare the energy from carbohydrates, fats, and proteins.

Getting Started

Purpose: To make and use a simple calorimeter to determine the amount of food energy in a marshmallow.

Materials

  • 4-×-10-inch (10-×-25-cm) piece of cardboard
  • aluminum foil
  • rubber band
  • scissors
  • modeling clay
  • cookie sheet
  • paperclip
  • large marshmallow
  • metric measuring cup
  • water
  • 1/2-pint (250-ml) canning jar
  • thermometer
  • match
  • 2 heat-resistant oven mitts
  • helper
  • timer

Procedure

  1. Wrap the cardboard in aluminum foil.
  2. Bend the covered cardboard to form a tube and secure it with the rubber band.
  3. Cut two small notches, one across from the other, in what will be the bottom of the cardboard tube.
  4. Place a walnut-size piece of clay in the center of the cookie sheet.
  5. Cover the clay with a small piece of aluminum foil to protect it.
  6. Straighten the paper clip, leaving a hook on one end. Stick the hooked end through the foil and into the clay so that the straight part of the wire stands vertically.
  7. Position the marshmallow on top of the wire so that it is secure.
  8. Use the measuring cup to pour 50 ml of water into the jar.
  9. Stand the thermometer in the jar of water.
  10. Read and record the initial temperature of the water.
  11. With the match, ignite two or three sides of the marshmallow.
  12. With your hands protected by the heat-resistant mitts, immediately stand the aluminum-covered tube over the burning marshmallow.
  13. Set the jar of water on top of the tube above the burning marshmallow (see Figure 5.1).
  14. Ask your helper to start the timer.
  15. When the marshmallow stops burning, ask your helper to stop the timer.
  16. Record the length of time the food burned.
  17. Immediately stir the water very gently with the thermometer.
  18. Read and record the final temperature of the water.
  19. Calculate the temperature change by taking the absolute difference (subtracting the smaller from the larger number) between the initial and final temperatures. See Appendix 1 for a sample calculation.
  20. Calculate the temperature change per unit of time by dividing the temperature change by the burning time.
  21. Construct a data table such as the one shown here.
  22. Calories Biochemical Energy

    Calories Biochemical Energy

Results

The author's results showed a change of 16°F (10°C) in 1.5 minutes, or 10.7°F (6.7°C) per minute.

Why?

Burning is a process by which oxygen combines with a substance and energy (ability to do work) is released. The burning marshmallow produces heat (a form of energy), which is indicated by the warming of the water. Animals are dependent upon internally generated heat, which is produced by a much slower "burning" process called respiration. In this chemical reaction, glucose combines with oxygen to produce energy. All foods can supply the body with energy. A calorimeter is used to measure the energy released when food burns.

The common unit of measuring energy is the calorie. A gram calorie (spelled with a lowercase c) is the amount of heat energy required to raise the temperature of one gram of water one degree Celsius. A food Calorie (spelled with a capital C) is the amount of heat needed to increase the temperature of 1,000 grams of water one degree Celsius. One food Calorie is equal to 1,000 gram calories. The food Calories of energy released during the burning of the marshmallow are absorbed by the water, thus raising the water's temperature.

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