Bomb Calorimetry of a Fruit LoopBy: Alexander Ward

CHM-352 – Dr. Lawrence

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Abstract: Bomb calorimetry is an experiment which quantifies the energy released upon combustion of a carbohydrate. This is useful in determining the amount of calories ingested, from a food product. The product being considered is a breakfast cereal called Fruit Loops from Kelloggs. After determining the variable, constant volume specific heat capacity, it is determined that the experimental value for 1 piece of Fruit Loop (3.762 ± 0.10 kJ) and commercial value (3.424 kJ) had a difference of +0.338 kJ.

Figure 1: Sample Bomb Calorimeter Configuration. Figure provided by Hope Chemistry Department.2

Introduction: Bomb Calorimetry is a method of quantifying the energy stored within a compound. Figure 1 shows the components of the bomb. The bomb is suspended in water, within a thermally isolated system to negate heat lost to the surrounding environment. The temperature of the water will increase based on the energy produced by a combustion of sample and wire. A stirrer aids in keeping the temperature of the water at equilibrium. An ignition unit is attached to an ignition wire, and is used to ignite the sample.

Materials and Methods: The bomb used for the experiment was a Parr Oxygen Bomb Calorimeter SN 1341EB, and the thermometer was a Digisense Thermaster 400 series, with an uncertainty of 0.01oC.

The ignition fuse used produces 1400 calg of energy when ignited. First, we recorded the mass of the

sample, too much sample. We cut about 10cm of fuse and recorded the mass. Using gloves or forceps to avoid contamination, we placed the sample pellet in the sample container, looped the fuse through the holes of the electrodes and clamped it down, allowing the fuse to touch the sample. We had assembled the bomb, screwing the cap down until snug. Afterwards, we filled the vessel with 25 atm of O2 gas, and released it to remove atmospheric gasses which may interfere with the experiment, and again, filled it with 25 atm of O2. The calorimeter bucket was filled with 2.0L of room temperature water using a 1.0L volumetric flask. We finished making the electrical connections to the top of the bomb, and placed it in the water pail and observe for air bubbles (leaks in the bomb apparatus). The lid of the insulation device was put on and we began stirring the water and observing the temperature using the

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thermometer inserted through the lid of the apparatus. We did not connect the fuse to the battery until ready to begin, to avoid premature ignition. After the temperature has equilibrated, we began recording the temperature for about 10 minutes before firing the ignition, and continued to record the temperature for a few minutes until there is no more change in temperature or temperature started to decline. After the sample has completely combusted, we vented the O2 before opening the bomb, and recorded the mass of the remaining fuse. We replaced the pail of water when moving to the next step of the experiment, the bomb apparatus had been cleaned and dried before the next experiment was performed.

Results: At constant volume; (1) ∆ E=cv∆T , where ΔE is the change in energy, cv is a constant and ΔT is the change in temperature which is experimentally obtained. The change in enthalpy, (2) ∆H=∆ E+∆(PV ), where ΔE is the change in energy, and Δ(PV) is the change in pressure and or volume. The volume is fixed because the reaction is taking place in a metallic casing. The pressure isn’t changing because the number of moles of gas is equal in both products and reactants, (3) CM (H 2O )N(s)+M ∙O2(g)→M∙CO2(g)+N ∙H 2O(l), where M and N are integers. This reaction shows that the number of moles of oxygen gas, M, is equal to the number of moles of CO2 gas, also M. Because the pressure and volume are not changing in this reaction vessel, the change in enthalpy is equal to the change in energy. First, we had determined the specific heat capacity by combusting a compound with a known ΔE of combustion, benzoic acid. At 298K, benzoic acid has a ΔE of combustion

of -3227 ± 4kJmol .

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Figure 2: Temperature vs Time during the combustion of Benzoic Acid. The initial temperature is 27.00o C, final temperature is 29.58o C, resulting in a change in temperature of 2.58o C. The change in temperature can aid in finding CV

(constant volume constant), to determine how much energy is produced when combusting an unknown sample.

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0 100 200 300 400 500 600 700 800 900 1000 110025.5

26

26.5

27

27.5

28

28.5

29

29.5

30

Time (s)

Tem

pera

ture

(oC)

The change in temperature from combustion derived from Figure 2 is equal to 2.58 ± 0.01K, the

mass of benzoic acid is 0.9993g with a molar mass of 122.12 gmol , while the mass of fuse combusted is

0.0085g. The energy produced by combustion of the fuse, Ewire=¿0.04979 ± 0.0006 kJ. The total energy produced is the combination of the energy produced by the sample and the energy produced by

the fuse, ∆ E, solving for equation 2, cv=10.26±0.04kJK .

The next experiment involved combusting a (several years old) Fruit Loop, one of Kellogg’s breakfast cereals. One serving of Fruit Loops is equal to 42.52 g of cereal, equal to 160 calories.3 The quantity of sample used was 0.2175 g. 3.424 kJ of energy will be produced due to the mass used, based on the value provided by the manufacturer.

0 100 200 300 400 500 600 700 800 900 100029.85

29.9

29.95

30

30.05

30.1

30.15

30.2

30.25

30.3

Time (s)

Tem

pera

ture

(oC)

Figure 3: Temperature vs Time during the combustion of a Fruit Loop. This figure indicates temperature drift before the initiation of the reaction. This thermal drift is due to the very small change in temperature observed, relative to the benzoic acid sample. The change in temperature is about 0.253o C without thermal drift correction.

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0 100 200 300 400 500 600 700 800 900 100029.9

30

30.1

30.2

30.3

30.4

30.5

30.6

30.7

Time (s)

Tem

pera

ture

(oC)

Figure 4: Temperature vs Time for the combustion of a Fruit Loop. The initial temperature of 30.20o C and a final temperature of 30.57o C, resulting in a ΔT of 0.37o C. Figure was corrected for thermal drift when recording the temperature.

Correcting for thermal drift in Figure 3, Figure 4 shows a higher change in temperature than figure 3. The wire combusted was 0.0052 g and the change in temperature is 0.37 ± 0.01 K. The energy produced by the fuse, Ewire=0.03050±0.0006 kJ . The energy of the sample is equal to the specific heat capacity multiplied by the change in temperature, minus the energy of the fuse, E sample=¿ 3.763 ± 0.10 kJ, a difference of 0.339 kJ.

Conclusion: The sample of Fruit Loop used for the experiment produced 0.338 kJ more energy that provided by Kelloggs. I thought this to be interesting, because I had thought the sample would produce less energy as the sample gets older. The difference in energy is small enough to suggest the manufacture supplied calorie quantity is accurate.

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References

(1) "Benzoic Acid." Benzoic Acid. N.p., n.d. Web. 24 Apr. 2016. <http://webbook.nist.gov/cgi/cbook.cgi?Name=benzoic acid>.

(2) "Bomb Calorimetry." Bomb Calorimetry. N.p., n.d. Web. 22 Feb. 2016. <http://www.chem.hope.edu/~polik/Chem345-2000/bombcalorimetry.html>.

(3) "Kellogg's Froot Loops Fruit Flavored Snacks, Letters & Numbers." Kellogg's Froot Loops Fruit Flavored Snacks, Letters & Numbers. Web. 14 Mar. 2016. <http://www.kelloggs.com/en_US/kelloggs-froot-loops-fruit-flavored-snacks-letters-numbers.html>.

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