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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