The Energy in Food. Energy (J/g) = (final temperature start temperature) x mass of water (g) x 4.2 (J per o C) Mass of food burned (g)

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1 The Energy in Food NAME DATE Food supplies energy for all animals without it we could not live. The quantity of energy stored in food is of great interest to humans. The energy your body needs for running, talking, and thinking comes from the foods you eat. Not all foods contain the same amount of energy, nor are all foods equally nutritious for you. An average person should consume a minimum of 2,000 kilocalories per day. That is equivalent to 8,360 kilojoules. Age/sex/occupation Energy needed per day (kj) Newborn baby 2000 Age Girl Boy Office worker Heavy manual worker Pregnant woman Breast-feeding woman You can determine energy content of food by burning a portion of it and capturing the heat released to a known amount of water. This technique is called calorimetry. The energy content of the food is the amount of heat produced by the combustion of 1 gram of a substance. It is measured in kilojoules per gram (kj/g). When we eat food, our bodies convert the stored energy, known as Calories, to chemical energy, thereby allowing us to do work. A calorie is the amount of heat (energy) required to raise the temperature of 1 gram (g) of water 1 degree Celsius ( C). When we talk about caloric values of food, we refer to them as Calories (notice the capital C ), which are actually kilocalories. There are 1000 calories in a kilocalorie. So in reality, a food item that is listed as having 38 Calories has 38,000 calories. Food energy can also be calculated in Joules. One calorie will equal 4.2 Joules Calories are a way to measure the energy you get from the food you eat. For this lab exercise, you will indirectly measure the amount of Calories in several food items using a calorimeter. So multiplying the rise in temperature of water by the mass of the water and then by 4.2 gives the number of joules of energy that were transferred to the water. Energy (J/g) = (final temperature start temperature) x mass of water (g) x 4.2 (J per o C) Mass of food burned (g)

2 Materials: -Graduated cylinder -Distilled water - Boiling tube - Clamp stand with clamp - Wood splints -Forceps - Popcorn - Crisp - Peanut probe - Scales - Weigh boat -Datalog with temperature Procedure 1. Calculate the mass of the weigh boat. Record your results. 2. Determine the weight of the peanut to the nearest 0.01 grams Record your data. (Resist eating any popcorn; they have to last through the lab.and there s no eating in lab.) 3. Using the graduated cylinder, measure out 25 ml of distilled water and pour into boiling tube. 4. Measure the initial temperature of the water to the nearest 0.1 degree (Ti). Record your data. 5. Attach boiling tube to ring stand clamp. Adjust the tube so it is at a 45 degree angle. 6. Carefully pick up the popcorn with your forceps. Using the Bunsen burner, light the food. 7. Once lit, put the food under the boiling tube over the flame to where the bottom of the tube touches the flame. 8. Allow the popcorn to burn until it goes out. If possible try to keep an eye on it and if it goes out quickly (less than a minute), relight 9. Once the popcorn has finished burning, carefully stir the water and then measure the temperature (Tf). You may have to leave the thermometer in the water for a while in order to get the highest reading. When the temperature begins to decrease record your data.\ 10. After the burnt popcorn has cooled, transfer it to the original weigh-boat (use the forceps if necessary) and weigh the remnants (wf). Record your data. 11. A calorie is the quantity of heat required to raise 1gram of water by 1 C. Calculate how many calories were released in the heating process by dividing the temperature change into the exact mass of water (in grams). Record your data. 12. Determine the Calorie of the popcorn. (#4) 13. Repeat Steps 2 11 with the crisp and peanut. Be sure to use new water. 14. Repeat the experiment using a 250 ml beaker

3 DATA Weight of weigh-boat:. Food Item Popcorn Crisp Peanut Initial Weight (wi) a Weight (Mass) of Food (g) a Final Weight (wf) a Mass of Sample Burned (Δw = wi wf) Initial (Ti) of Water ( C) Final (Tf) Change in (ΔT = Tf Ti) a Don t forget to subtract the weight of the weigh-boat. 15. Determine the Joules of the food: - Make sure you show all your and you include all proper units Food Popcorn Crisp Peanut joules = change in temperature x mass of water* x 4.2 mass of the food burned J/g = kj the mass of the initial sample weight. Energy or Kilojoules (kj) calories (J) kj/g *Remember that the density of water is 1g/ml therefore 1 g of water = 1 ml of water

4 CONCLUSIONS: 1. Were you able to determine the entire joule content of the food item? Why or why not? 2. What is the original source of energy in all of the foods tested? 3. Which of the tested foods is the best energy source? Why?

5 4. Why might some foods with lower energy content be better energy sources than other foods with higher energy content? 5. Would you expect the energy content values that you measured to be close to the value listed in dietary books? Why?