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Bomb calorimetry. The goal of this experiment was to use temperature data over time from combustion reactions to calculate the heat released and then produce an experimental value for the heat of formation of naphthalene.

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Introduction

Experiment 1. BOMB CALORIMETRY Experiment Date: Jul 27, 2012 Formal Report: Aug 1, 2012 Student name: Suri Hoang (220080192) Abstract The goal of this experiment was to use temperature data over time from combustion reactions to calculate the heat released and then produce an experimental value for the heat of formation of naphthalene. After running a calibration trial of benzoic acid in the bomb calorimeter, the heat capacity of the calorimeter was 0.0699 kJ K-1. Using this value, the experimental enthalpies of combustion for naphthalene were -4982.66 ± 99.6532 kJ mol-1 which was a 3.44% error from the literature value of -5160 ± 20 kJ mol-1 (NIST Chemistry WebBook, 2008), and the enthalpy of formation was -86.8478 ± 1.736956kJ mol-1. Errors to account for in this experiment were due to the accuracy of weighing the substances, reading the thermometer, the measurement of water. Overall, this experiment was a success as each objective of the experiment was completed and the experimentally determined enthalpy of combustion of solid naphthalene was very close to its literature value. Introduction To find heats of combustion for certain reactions, it is feasible to use a bomb calorimeter. Due to heavy insulation, a calorimeter is adiabatic. Thus, the system is isolated from the environment. This way, combusting a chemical sample in the calorimeter and using temperature measurements makes it possible to find the heat released. ...read more.

Middle

Mass Platinum wire Cotton Water Benzoic acid 0.7408± 0.0148g 8± 0.16 cm 7.5 ± 0.15cm 10 ± 0.2ml Naphthalene 0.5025± 0.0101g 8 ± 0.16cm 7.5± 0.15 cm 10± 0.2ml The temperature were read and recorded every minute for 5 minutes (the first five results in Table 2) before firing the bomb. The bomb was then fired and recorded the time and temperature every 30 seconds until 15 minutes after the temperature reaches to maximum (From minute 5.30th to the end, Table 3). After 48 minutes for benzoic acid combustion and 45 minutes for naphthalene combustion (Counting from the samples were burnt), all benzoic acid and naphthalene has been burnt and no specks of carbon on the walls. Finally, all parts of the bomb were cleaned and dried. Results The heat of combustion of naphthalene was experimentally calculated to be -4982.66 ± 99.6532 kJ mol-1 and the enthalpy of combustion of naphthalene was experimentally determined to -4983.1522 ± 99.6630 kJ mol-1 which was a 3.44% error from the literature value of -5160 ± 20kJ/mol (NIST Chemistry WebBook, 2008). In order to calculate these results, the heat capacity of the calorimeter had to be determined by combusting benzoic acid, which had a known heat of combustion value. The heat capacity of the calorimeter was 0.0699 kJ K-1. The uncertainty of each calculation in this experiment was determined by completing a propagation of error calculation. ...read more.

Conclusion

For example, one source of error was that exactly the same amount of water needed to be used to immerse the bomb in both trials for the best results. The water was measured out using the human eye and therefore, the accuracy of its measurement is not reliable. The other main source of error is that the actual combustion of either solid was not the only source of heat transfer in the calorimeter. Stirring in the calorimeter produced a certain amount of heat and then another certain amount of heat was lost through the walls of the calorimeter. The results of this experiment would be useful for calculating other thermodynamic properties of naphthalene, since many of those calculations would require that the enthalpy of combustion of naphthalene be known. Consequently, the heat of combustion of naphthalene was experimentally calculated to be -4982.66 ± 99.6532 kJ mol-1 and the enthalpy of combustion of naphthalene was experimentally determined to -4983.1522 ± 99.6630 kJ mol-1 which was a 3.44% error from the literature value of -5160 ± 20kJ/mol (NIST Chemistry WebBook, 2008) and the enthalpy of formation was -86.8478 ± 1.736956kJ mol-1. In order to calculate these results, the heat capacity of the calorimeter had to be determined by combusting benzoic acid, which had a known heat of combustion value. The heat capacity of the calorimeter was 0.0699 kJ K-1. The use of bomb calorimetry to calculate the heat of combustion of naphthalene was successful due to the low error between the experimental results and literature values. ...read more.

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