1/28/09
Calorimetry of
Fuels and the Use
of Energy to Do
Work
The Energy-Work Connection
This experiment will be done on
nd
rd
February 2 & 3 , in place of
“The System” experiment.
Adapted by Caitlin Conn and Patrick Crooks from
The Chemurgy of Peanuts by Genevieve Miller
Introduction
NOTE: If you are allergic to peanuts, please inform your instructor or TA immediately so
that you can be assigned a different lab.
Energy is crucial to the survival of every living thing. As humans, our bodies need to remain
within a relatively narrow temperature range. We “burn food” (internally) to stay warm.
Additionally, because all systems tend to move toward disorder without an input of energy, we
would die without food. We need bodily fuel so that we can function, and we burn it when we
walk, talk, sleep, exercise, and study.
You may have heard of “burning calories” in reference to exercise. Please note that calories are
never burned. A calorie is simply a measure of energy, and that energy is actually released
during a combustion reaction. During exercise, the body burns food to release energy, and that
energy can be measured in different units, such as calories.
Combustion reactions take place within our bodies when we burn food. A combustion reaction is
defined in Chemistry: The Central Science as “[a] chemical reaction that proceeds with evolution
of heat and usually also a flame.” This textbook goes on to say that most combustion reactions
involve oxygen (1).
Different fuels can be burned to release energy. Food, for example, is a type of fuel burned by
the body. Another type of fuel with which you will use in this experiment is paraffin. Paraffin is
the material of candles. When you burn a candle, the paraffin is combusted, and heat is released.
The energy released by paraffin combustion can be used to light or heat areas of different sizes,
depending upon how much paraffin is combusted. You will be determining the energy released
by the combustion of paraffin as part of this lab.
You will also examine the calorie content of a common food item, peanuts. If you have a peanut
allergy, please tell your instructor or your TA right away so that you can be assigned a different
makeup lab. Peanuts are used in a variety of different food items, and also in substances like
cosmetics and paint. George Washington Carver was largely responsible for identifying the
many different uses of peanuts and for using peanuts to serve many different purposes (2).
To calculate the energy content of different substances, you will be building your own
calorimeter out of household items. A calorimeter is defined as “an apparatus that measures the
evolution of heat” (1). You will burn several substances and use temperature changes in water to
determine the energy released by the combustion. Then you will answer theoretical questions to
help you understand the connections between calories and work.
You will need to use the textbooks provided for you in your classroom in order to complete some
parts of this lab. Please make sure to cite these sources properly.
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Background Chemistry
Overview
The metabolic reactions that take place inside our body are vital to our existence. One of the
most fundamental examples of metabolism is digestion. The process of digestion is most
certainly a chemical one – it is an example of a combustion reaction: food reacts with oxygen to
generate energy.
Foods produce the same amount of energy whether they undergo combustion under metabolic
conditions or they are burned outside the body. We can, then, calculate the energy value of food
by burning it and measuring the amount of heat that is released from the reaction. To ensure
accuracy, chemists use calorimeters, devices that measure temperature changes from chemical
reactions, to determine the energy produced by a reaction.
Food energy is measured in Food Calories (with a capital “C”). One “Food Calorie” is 1000
times bigger than a “scientific calorie” – that is, 1 Cal = 1 kcal = 1000 cal. One calorie is the
energy required to raise the temperature of 1 g of water by 1 °C from a standard temperature at 1
atm pressure. Throughout this lab, we will use Calorie with a capital “C” to indicate Food
Calories.
In this experiment, you will measure the amount of energy released by the combustion of several
different fuels. The energy released during the combustion will raise the temperature of a
measured volume of water in a simple calorimeter. We can determine the exact amount of
energy released because we know the specific heat of water. The specific heat of water is 1.0 cal
per g per °C, or 1 Cal per kg per °C. By measuring the temperature change in a known mass of
water, you can determine the amount of energy.
Energy released = (mass of H2O heated) * (temperature increase) * (specific heat of H2O)
(Eqn. 1) (2)
Paraffin Calorimetry
Paraffin can be burned to release energy. Typically, the energy content of paraffin, which is
found in candles, is 10.0 k cal/g (3). Another word for paraffin is “alkane,” which is a particular
type of organic molecule. Just as there are many alkanes, there are many different kinds of
paraffin. Most paraffins are not very reactive at room temperature and one atmosphere pressure,
but they can be combusted by increasing temperature and/or pressure. Paraffin combustion
produces water and carbon dioxide and releases energy (4).
Besides being used in candles, paraffin was being considered as a potential rocket fuel as of
2003. NASA noted the increased safety and decreased pollution that would result from using
paraffin as an energy source (5). Paraffin is also used as a cosmetic and is frequently applied to
the skin to soften it.
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Peanut Calorimetry
Peanuts are known for their high energy value. On average, a peanut contains 6 Cal per g of
energy. In fact, one pound of peanut butter contains the same food energy found in 32 eggs or
2.5 pounds of steak. It is this energy value and the low cost of producing peanuts that led Carver
to stress their importance during the Depression.
Peanut oil can be represented by the following molecule with molecular formula C57H104O6.
Please note that at each vertex, carbon and hydrogen are present. Each vertex represents one
carbon, and hydrogens are attached so that each carbon has four bonds.
Figure 1. The molecular structure of peanut oil. (2)
The combustion reaction for peanut oil, given in Figure 1, is shown in Equation 1.
C57H104O6 (l) + 80 O2 (g) 
(2)
57 CO2 (g) + 52 H2O (l) + heat
(Eqn. 2)
Energy Conversion
Energy can be measured in many different units. You may need to refer to the textbooks
available to you in the classroom to complete some of the questions in this lab. You will also
need to understand foot-pounds. A foot-pound is the energy required to lift one pound one foot
high. 1 calorie = 3.08 foot-pounds, 1 Joule = 0.738 foot-pounds, 1 calorie = 4.18 Joules (6)
You will use this information to relate energy and work. Be sure to properly cite any additional
sources that you find in your classroom library and use to complete your questions.
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References
1. Brown, Theodore L., H. Eugene LeMay, Jr., and Bruce E. Bursten. Chemistry: The
Central Science. 10th Edition. Page G3. Pearson Education, Inc: Upper Saddle River, NJ,
2006.
2. Miller, Genevieve. The Chemurgy of Peanuts. Chemistry 111 Makeup Lab. Spring 2008.
3. “The Energy Content of Fuels: A Physical Science Activity.” University of Virginia
Physics Department. October 25, 2008. <http://galileo.phys.virginia.edu
/outreach/8thGradeSOL /FuelEnergy.htm>.
4. McMurry, John. Organic Chemistry. 7th Edition. Page 91. Thomson Learning, Inc:
Belmont, CA, 2008.
5. “Candle Stick Rocketship.” NASA. January 9, 2003. October 25, 2008. <
http://science.nasa. gov/headlines/y2003/28jan_envirorocket.htm.
6. Walker, Jearl. Fundamentals of Physics Part 3. John Wiley and Sons, Inc: Hoboken,
2008.
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NJ,
Additional Reading
1. Markow, Peter G., Estimating the Calorie Content of Nuts, Chemical
Education Resources, Inc., Pennsylvania,1993.
(Many of the experiments in Genevieve Miller’s make-up lab, Reference 2, are
based on this publication.)
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Quiz Outline
There will not be a quiz on this lab. A post-lab
quiz on Experiment 3 (Small Scale Techniques)
will be given on the day of the experiment.
NOTE: Please bring an
empty soda can (or two!) to
lab for this experiment.
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Laboratory Experiments
Flowchart of the Experiments
Section A. The Construction of a Calorimeter
Section B. Thermodynamics of a Burning Candle
Section C. Combustion of a Peanut
Section D. Energy and Work
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Section A. The Construction of a Calorimeter
Goal:
To build a functional small-scale calorimeter that is capable of
determining the amount of heat released in a chemical reaction.
Before You Begin:
You are about to build a device similar to the one in the diagram shown
below. As you work through this section, refer to the diagram to facilitate
your own construction. You may work in pairs for this experiment.
Small-scale calorimeter.
Experimental Steps:
1.
Obtain 1 empty aluminum soda can, 1 metal triangle,
a square piece of cardboard about 15 cm x 15 cm,
a ring stand, (this consists of a stand, a ring, and a clamp)
and a thermometer. These materials will be used to
construct your calorimeter.
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2.
Suspend your can in the middle of the ring using the
provided materials. Experiment with different set-ups if
necessary. You may not need to use all the provided
materials. Check with a TA to make sure your set-up is
sufficient.
3.
Place the cardboard square on top of the can, and put a
mark on the place directly above the hole in the top of the
soda can. Punch a hole in the cardboard square at the
spot you marked, and insert the thermometer in this hole.
The hole should be small enough to hold the thermometer
in place. Place the cardboard square on top of the soda can
and adjust the position of the thermometer until the bulb
extends into the can about 5 cm from the bottom.
Section B. Thermodynamics of a Burning Candle
Goal:
Experimental Steps:
To observe the thermodynamic change of a burning candle using the
homemade calorimeter.
1.
Carefully measure 200.0 mL of room temperature distilled
water. Note: the distilled water spigots can be rotated
outward to fill large containers more conveniently.
Remove the thermometer assembly from the soda
can and pour the water into the can.
2.
Reposition the thermometer assembly and measure the
initial water temperature. Record this temperature in your
lab notebook.
3.
Obtain a candle and the bottom part of a petri dish(the
smaller part). Stand the candle up in the petri dish.
4.
Determine the mass of the combined candle, and petri
dish. Record your value.
5.
Transfer the candle and dish to the ring stand, directly
underneath the calorimeter. Adjust the can clamp so that
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the bottom of the can rests 1-2 cm above the top of the
candle.
6.
Light the candle and let it burn. When the temperature of
the water has risen by approximately 10 degrees, blow out
the candle and record the final temperature of the water.
7.
Again, find the mass of the candle and petri dish system
Record your value.
Q1.
Find the energy released per gram of paraffin. Put your
answer in terms of Food Calories/g.
Q2.
The accepted energy content value for paraffin is
10.0 kcal/g. Convert this value to Food Calories per gram.
Q3.
How does the value you found compare with the accepted
value of the energy content of paraffin? Calculate your
percent error.
Q4.
(a) What are some possible sources of error in this
experiment?
(b) What is the largest source of error?
(c) What can be altered in the experiment to improve the
accuracy of the calorimeter?
9.
Make any change to your calorimeter that you think will
improve its accuracy and repeat steps 1-8.
Q5.
(a) What change did you make to your calorimeter?
(b) Did you get a more accurate result for the energy
capacity of paraffin?
Q6.
Create a table that organizes all of your data from both
trials.
Q7.
Patrick thinks that burning the candle until the temperature
has risen only 5 degrees will yield more accurate results,
but Caitlin thinks that it won’t make a difference. Who is
right, and why?
Section C. Combustion of a Peanut
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Goal:
To observe the thermodynamic change of a burning peanut using
the homemade calorimeter.
Experimental Steps:
1.
To construct a peanut support stand, first obtain a paper
clip and a cork.
2.
Straighten one end of the paper clip. Insert the end of the
paper clip into the center of the end of the cork which has
the small diameter. You will place the peanut support
stand on the base of the ring stand used in the calorimeter
assembly. (See figure in Section A).
3.
Carefully measure 200.0 mL of room temperature distilled
water. Remove the thermometer assembly from the soda
can and pour the water into the can. Record the amount of
water used.
2.
Reposition the thermometer assembly.
3.
Select half of one peanut for your study.
4.
Determine the mass of the peanut half. Record this value.
5.
Transfer the peanut half to the support stand by inserting
the free end of the paper clip into the peanut half. Position
the peanut support stand underneath the can so that the
peanut is 1-2 cm below the bottom of the can.
6.
Measure the initial water temperature. Record this
temperature.
7.
Ignite the peanut. (This may take several attempts…be
careful not to burn yourself.) Extinguish the match by
putting it into some water.
8.
Immediately after the peanut stops burning, determine the
final temperature of the water. Record this temperature.
9.
What remains of the peanut is called the “peanut residue”.
Allow the peanut residue to cool to room temperature.
Determine the mass of the peanut residue.
10.
Record the mass of the peanut burned by subtracting the
mass of the peanut residue from the initial mass of the
peanut.
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Q8.
Calculate the average amount of energy released per gram
of peanut burned in Food Calories/g.
Q9.
Find the accepted value for the energy content of a peanut
in Food Calories/g by reading the nutrition information on
the peanut bag. Calculate percent error of your value
compared to the accepted value.
11.
Repeat steps 3-10, this time using a whole peanut.
Q10.
Calculate the average amount of energy released per gram
of peanut burned. How does this value compare to that of
the first trial using the peanut half? Should these values be
different? Why or why not?
Q11.
Create a table that organizes all of your data from both
trials.
Q12.
The peanut residue looks very similar to charcoal, a
compound of pure carbon. Consider the combustion
reaction of charcoal and use enthalpies of formation to
calculate a theoretical energy yield for the peanut residue.
(Use data from either trial).
Hint: C (s) + O2 (g) → CO2 (g)
ΔHf of Carbon Dioxide = -393.5 kJ/mole
Q13.
Add the energy released by the burning peanut with the
theoretical energy of the peanut residue to get the total
theoretical energy of the peanut. Divide this by the original
mass of the peanut to get a theoretical energy of the peanut
in Food Calories/g. How does this value compare to your
previous calculated values? How does it compare to the
accepted value?
Section D. Energy and Work
Goal:
Experimental Steps:
To theoretically relate energy and work concepts.
1.
One foot-pound is the amount of energy expended when a
force of one pound acts through a distance of one foot
along the direction of the force. Have one lab member
perform an action of work and convert the amount of work
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done into foot-pounds. (Ex: step up 0.5 foot on a stool rung
or lift a 1-pound book three feet)
Q14.
Convert the amount of work you just did into Food
Calories.
Q15.
(a) Guess how many grams of peanuts you would have to
eat to do the amount of work you did in question 1.
(Assume that all the potential energy in the peanut is
completely combusted in the body and turned into usable
energy).
(b) Now calculate how many grams of peanuts are required
using the nutritional information from the peanut label.
Q16.
Was your guess higher or lower than your calculated
value?
Q17.
When running, a person can burn 0.653 Food Calories/
mile/pound. How many food calories does a 150-pound
person burn after running a mile?
Q18.
Theoretically, how many grams of peanuts would you have
to eat to run a mile? (Assume, again, that all the potential
energy in the peanut is completely combusted in the body
and turned into usable energy.) Does this answer surprise
you?
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