Determining the Caloric Energy in Food
Calorimetry is a technique that is used to determine the amount of heat gained or lost
during a chemical reaction. A calorie is the energy needed to raise the temperature of 1
gram of water 1 degree Celsius. Our energy is obtained from the “burning” of the food
we eat by our body.
One can find out how much energy their body will be able to get from food by looking at
the Nutrition Facts on the package. The number of Calories represents the amount of
energy the food can liberate during the chemical reactions of the digestion process.
Keep in mind, when looking at a nutrition label, the value of 200 “Calories” is really
equivalent to 200,000 “calories”; the capital “C” implies kilocalories. Therefore, if a
person is on a 2,000 Calories per day diet, then they need to consume enough food that
contains a total of 2,000,000 “calories” for the entire day.
To determine the heat energy in a food item, or calories, you can burn it in a special
container called a calorimeter. By burning pieces of food, the chemical energy stored in
molecular bonds is released as heat and light. This type of reaction is called an
exothermic reaction since heat is being generated. The more calories a food contains,
the more heat is given off when burned. Foods high in calories will release large
amounts of energy, and foods high in protein will release fewer calories than an equal
amount of fat.
In this experiment the heat energy from the burning food is used to raise the
temperature of water. When the food burns itself out, the temperature increase of the
water can be used to calculate the total heat energy released from the food. According
to the law of conservation of energy, the heat lost by the food will be gained by the
water.
The heat absorbed by the water depends on the mass, physical make up and
temperature change the water experiences. In equation form this is represented by:
Q = mCpΔT
Since the heat lost by the burning food is equal to the heat absorbed by the water:
Heat emitted by the reaction = Heat absorbed by the water
The specific heat for water is 1.0 calorie/gram degree C.
Materials:
Food item with Nutrition Facts
Calorimeter
250mL Erlenmeyer flask
Match or lighter
PASCO Temperature probe - You can use EZ Temperature or Data Studio
Water
Balance
Tongs
Goggles
Watch glass
Aluminum foil
Procedure:
1 Obtain a dry watch glass. Place aluminum foil around the watch glass. Record
the mass in the data table.
2 Place the dorito on the watch glass and obtain the mass of the item and the
watch glass. Subtract the empty watch glass mass from the total mass to obtain
the initial mass of the dorito. Record these values in the data table.
3 Obtain the mass of a clean dry 250mL Erlenmeyer flask. Record the mass in the
data table.
4 Fill the flask with ~100mL of water. Record the mass of the flask and water.
5 Subtract the initial mass of the glass flask from the final mass of the glass flask
and water. This will yield the mass of the water only. Record the mass of the
water in the data table.
6 Measure the initial temperature of the water in the flask and record in the data
table.
7 Set up the calorimeter (tall metal box) so the flask is on top of the metal cylinder,
but hanging from the top plate into the center of the metal cylindrical tube.
8 Place the dorito in the cylinder so it is under the flask.
9 Use a match to light the dorito. Place the cylinder back over the food so the flask
is directly over the flame. Always use caution when working with fire.
10 Allow the dorito to burn out completely.
11 Once the dorito has burned out completely, record the final temperature and
calculate the temperature change.
12 Using hot gloves or tongs, remove the cylinder and carefully place the watch
glass with the food remains on the balance to measure the remaining mass.
13 Record the final mass of the food in the data table and calculate the mass that
was lost.
Data Table
copy onto looseleaf paper to hand in
Food Item
Mass of empty watch glass (g)
Mass of food item and watch glass (g)
Initial mass of food item (g)
Final mass of remaining food item (g)
Mass of food lost due to burning (g)
Mass of empty flask (g)
Mass of flask and water (g)
Mass of Water Only (g)
Initial water temperature (C)
Final water temperature (C)
Change in water temperature (C)
Calculations:
1 To calculate the total calories of heat energy the water gained use the heat
equation and the fact that the specific heat of water is 1 calorie/gram degree C.
2 Determine the calories per gram the food item produced (Calculation from
number 1 divided by the mass that was burned away). For example, if 10
calories of heat were gained by the water and 5 grams of food were burned
away, then 10 calories/5 grams yields 2 calories/gram.
3 To determine the food calories, use the information found in the Nutrition Facts
label from your food item.
a. Serving size (from label): ____________________g
b. “Calories” per serving size (from label): ____________ Calories
c. Multiply the Calories by 1,000 to find calories: ________ calories
d. “calories” per gram of food item: _______________ cal/g
4 Determine the percent error for the calories/gram between your experimental
value (experimental = answer from #2) and the accepted value from the
nutritional information section on your food item (accepted = answer from #3d)
Percent error = |experimental - accepted|
accepted
x 100
5. When food burns, it loses mass. Since mass can not be lost, only transformed into
different types of energy, what other types of energy was the mass transformed into?