Biology 4: Energy in Foods

Safety note: In todays lab there will be fire. We will be burning things. Be careful. Tie your hair back if it is long. Be careful with your sleeves. Always wear your goggles. Dont touch anything that might be hot. Introduction: As we have been discussing in class, food has potential energy that is released in our cells. We say that our body is burning food, because it is basically the same chemical reaction as burning the food for real. When this reactions happen outside of our body, it is called combustion. When this reactions happen inside of our cells, it is called cellular respiration. In each case, the amount of energy released is the same. One unit used for measuring energy is the calorie. We will be measuring energy in calories in this lab. Supply the definition for a calorie below: calorie -

When energy is added to a mass of water, the temperature of the water increases. Write a mathematical equation below that relates these four variable: mw = mass of water in grams, T = change in temperature in C, Cw = specific heat of water in cal/g/C and Qc = energy collected by the water in calories.

Purpose: In todays lab, you will be burning foods under a cup of water to determine the energy content of the food. You will then calculate the energy content of the food in kilocalories per gram. Procedure: Mr. Daly will show you the apparatus we will be using today to measure the energy content of these foods. It is called a calorimeter. Draw a picture of it in the space provided:

The idea behind a calorimeter is that the energy released by the burning food will heat the water in the container. Of course, not all of the heat is going to get absorbed by the water. Some heat will be lost to the environment. The ratio of heat trapped to heat lost is the efficiency of the calorimeter. Well call that variable E. Qb will represent heat released during burning and Qc will stand for heat captured by the calorimeter. Write an equation below relating E, Qc, and Qb. In order to figure our the efficiency, E, of the calorimeter we will need to burn a food whose energy content is known. Thats where the marshmallows come in. Youll burn a few marshmallows under the

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Energy in Foods

Biology 4: Energy in Foodscalorimeter and calculate the energy captured by the calorimeter. Mr. Daly will provide you the energy content of the marshmallows. This will allow you to calculate the efficiency of the calorimeter. Then you will burn a cheeto in your calorimeter. You will use the equations provided above and the efficiency of your calorimeter to calculate the calories per gram of cheetos. You can handle the calculations, but here is a data table to help you keep track of your data:

Marshmallows (run 1)

Marshmallows (run 2) Cheetos (run 1) Cheetos (run 2)

Mass of food, initial (g)

Mass of food, final (g)

Mass of food combusted (g)

Mass of Erlenmeyer flask, empty (g)

Mass of Erlenmeyer flask, with water (g)

Mass of water (g)

Water temperature, initial (C)

Water temperature, final (C)

Change in water temperature (C)

Energy density (calories per gram)

Average energy density (cal/gram)

Efficiency of Calorimeter (%)

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Biology 4: Energy in FoodsIn addition to this completed table, you must write a paragraph (at least 6 sentences) summarizing what your learned in this lab and answer the following questions. These should be handed in attached to this sheet. 1) Was this an exergonic or endergonic reaction? This reaction was a exergonic reaction because we burnt a lot of the food samples and the water didn't absorb all the energy. An exergonic reaction releases energy while endergonic reactions absorb energy. 2) On average, which were stronger, the bonds in food and oxygen or the bonds in CO2 and H2O?

How do you know? The bonds in CO2 and H2O are stronger because those molecules release more energy being made than the amount of energy needed for food and oxygen molecules are being broken. 3) Draw an energy diagram for the reaction that occurred. Label the reactants, products and activation

energy. Make sure that your axes are labelled.

4) Some people say that our bodies burn food. Where does this burning process take place and what is it called?

This burning takes place in the mitochondria and it is called Cellular Respiration.

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