Lab Report 18 - CHEM 106. Hunter College. Calorimetry and Combustion.
Name: __________ Grade: 100
TA: _____________
Date: 11/16/19
Ex 18. Calorimetry and Combustion
Introduction
Calorigenic nutrients, such as carbohydrates, fats, and proteins, release energy through
combustion reactions.1-2
For this particular experiment, we will calculate the amount of heat
released when different snacks burn, which in turn will determine the calories or energy content
of the given snacks (expressed in units of kilojoules (kJ) or kilocalories (kcal)). To quantify the
energy content, a bomb calorimeter will calculate the heat absorbed or given off by a known
system (glucose), to its surrounding (the water in the calorimeter). As the hydrogen atoms in
glucose (C6H12O6
) transfer to oxygen, the organic molecule liberates energy.1-2
Thus, we will be
able to relate the temperature change (∆T) produced in the water, to the amount of heat energy
(q) absorbed (or released) by the combustion reaction of C6H12O6
. Using this as a baseline, we
will then determine the energy content of the various given snacks.
Materials
Part 1: Determine the Calorimeter Constant
3.00 grams of glucose (C6H12O6
) was placed in a bomb calorimeter. Initial temperature inside the
colorimeter (24.90 °C) and final temperature (29.20 °C) was used to compute the ΔH°
rxn
for the
combustion of C6H12O6
.
Part 2: Energy Content of Various Snacks
The energy content in (Cal/oz) was calculated for several food samples, based on the mass (g)
and temperature (°C) provided in the lab manual. Percent error was estimated for each sample.
Snacks were then ranked from lowest to highest energy content.
Observations and Experimental
Part 1: Determine the Calorimeter Constant
The 3.00 grams of C6H12O6
, placed in the bomb calorimeter, caused initial temperature to change
by 4.30 °C. The ΔH°
rxn
for the combustion of C6H12O6
was calculated (Table 1) using several
calculations and equations (see sample calculations).The calorimeter constant was determined
(9.827 kJ/°C).
Part 2: Energy Content of Various Snacks
Using several calculations (see sample calculations), the energy content for several snacks was
determined, using the mass and temperature given in Table 2. Percent error was relatively low in
the experiment (8.07±13.97%), with a high percent error of 36% in the trial examining beef
jerky. Snacks ranked in terms of highest energy content (Cal/oz) to lowest was observed in the
salted peanuts, cheetos, oreos, popcorn, and beef jerky, respectively.
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Table 1. Data for the Combustion of Glucose
Sample M (g) nGlucose Ti
(°C) Tf
(°C) ΔT qcomb (kJ) qcal (kJ) CCal (kJ/°C)
C6H12O6 3.00 0.01665 24.90 29.20 4.30 - 42.258 42.258 9.827
Note: CCal
: Calorimeter Constant. C6H12O6
: Glucose. M: Mass. n: Mole. Ti
: Initial Temperature. Tf
: Final Temperature. ΔT:
Change in Temperature. qcomb
:Heat released in combustion. qcal
: Heat absorbed by colorimeter.
Sample Calculations For Part 1: Determine the Calorimeter Constant
C6H12O6 (s) + 6 O2 (g) ⇌ 6 H2O(g) + 6 CO2 (g) + Δ
Heat
Equation 1.
ΔH°
rxn = [6 (ΔHf CO2
) + 6 (ΔHf H2O)] - (ΔHf C6H12O6
) → [(6 (- 393.5 kJ/mol)) + ((6 (- 242.0 kJ/mol))] - (-1275 kJ/mol)) → (- 2,538 kJ)
qcomb = n Hrxn = - 2,538 kJ x 3.00 g = - 42.258 kJ → qcal = - qcomb → 42.258 kJ
180.1559 g
Ccal = qcal = 42.258 kJ = 9.827 kJ/°C
T 4.3 °C
Table 2. Energy Content of Various Snacks based on Mass and Temperature.
Sample M (g) Ti
(°C) Tf
(°C) ΔT qcal (kJ) qcomb (kJ) E (kJ/g) E (Cal/oz) E
Label (Cal/oz) % Error
Oreo 2.41 26.12 30.92 4.80 47.17 - 47.17 19.57 132.2 133.4 0.90
Popcorn 2.29 25.76 29.95 4.19 41.18 - 41.18 17.98 121.8 122.8 0.81
Cheetos 2.21 25.13 30.49 5.36 52.67 - 52.67 23.83 161.5 160.0 0.93
Beef Jerky 2.23 25.89 29.54 3.65 35.87 - 35.87 16.08 109.0 80.00 36
Salted Peanuts 2.45 25.64 31.79 6.15 60.44 - 60.44 24.67 167.1 170.0 1.7
Note: Data was rounded to four significant figures. Percent error was rounded to two significant figures.
Abbreviations: C6H12O6
: Glucose. E: Energy Content. E Label
: Energy Content Listed on Label. M: Mass. Ti
: Initial Temperature. Tf
Final Temperature. ΔT: Change in Temperature. qcomb
: Heat released in combustion. qcal
: Heat absorbed by colorimeter.
Sample Calculations For Part 2: Energy Content of Various Snacks
Oreo Cookies:
Theoretical Cal from g to oz:
E
Label
(Cal/oz) = 160 Cal × 28.3495 g = 133.409 Cal/oz
34 g 1 oz
Calculate amount of q in 2.41 g:
qcal = CcalΔT = 9.827 kJ x 4.80 °C = 47.1696 kJ → qcomb = - qcal → - 47.17 kJ E (kJ/g) = - qcomb = - (- 47.17 kJ) = 19.572 kJ/g
°C M (g) 2.41 g
E (cal/oz) = 19.572 kJ x 6.7757 Cal = 132.23 Cal/oz
1 g 1 oz
% Error = |Theoretical Value - Experimental Value| x 100% = |133.41 - 132.2| x 100% = 0.89955 % → 0.90%
Theoretical Value 133.4
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