Energy in Snacks Lab

Energy Value of Snacks

Problem: How much heat is available from the combustion of peanuts, almonds, and other snacks? Can this heat be measured?

Objective:  When you eat food, your body is actually “combusting”-burning the food.  The fat, protein and carbohydrates react with the oxygen in your body to produce carbon dioxide and water.  You will choose three types of snack to burn and measure the amount of energy released via water being heated by flame.  Unfortunately, we will lose a lot of heat to the surroundings and we also will have to heat the aluminum can as well. 

Pre-Lab Questions:

1. Look at the set up for the lab, explain which part is exothermic and which part is endothermic and tell why.

2. If a bag of potatoes weighs 5 pounds and costs $1.35.  How much does it cost per pound?

3. What if you only use 3 pounds of the potatoes and the other 2 pounds go bad. If the bag still costs $1.35 what is the cost per pound of what you actually used?

1. Hypothesis: Predict which snack of the three you are testing——will furnish the greatest amount of energy per gram. Remember that it is not about which is the heaviest but which has more amount of energy per gram. Explain your hypothesis.

2. Data Table: Make sure to write units

	Trial #1—type of nut ___________	Trial #2—type of nut _________	Trial #3—type of nut _________
Mass of snack (initial)
Mass of can
Volume of water
Temperature initial of water
Temperature final of water
Mass of leftover snack

3. Determine the change in mass of each snack from before and after combustion.

     Mass of nut (initial) – mass of leftover nut = mass of nut that combusted

4. Determine the change in temperature of water (and therefore, also the can) before and after combustion.

          Temperature final – Temperature initial = Temperature change

5. Determine the heat absorbed by the water, using the equation Q = s x m x DT

          (specific heat for water is 4.18 J/g×C°)

                                                                                                             

6. Determine the heat absorbed by the can, using the equation Q = s x m x DT

          (specific heat for aluminum is 0.9 J/g×C°)

7. Determine the total heat absorbed by the water and the can. Add #5 + #6.

          NOTE: This is also equal to the heat released by the snack.

8. Determine the total heat released per gram of nut. #7 divided by #3.

          Divide by the total heat by the total gram of nut that combusted.

9. Summary Table

	Trial #1—type of snack	Trial #2—type of snack	Trial #3—type of snack
Mass of combusted nut #3
Change in Temperature (DT) #4
Heat absorbed by the water #5
Heat absorbed by the can  #6
Total heat absorbed #7
Total heat released per gram of nut #8

10. Critique the procedure used in this experiment. Do you expect the procedure to give an accurate energy value for the nuts? Explain your answer.

11. Draw a model of the set up before it is lit and then a second model after it is lit to show the direction of the heat flow and which part is exothermic and endothermic.  Remember to draw what is happening to the molecules!