Resonance Energy of Naphthalene by Bomb Calorimetry
Experiment 3: Resonance Energy of Naphthalene by Bomb Calorimetry
CHEM 457: Lab Section 4
Lab Group #3:
The enthalpy of combustion of naphthalene was experimentally determined to be -5030.44 ± 78.98 kJ/mol which was a 2.5% error from the literature value of -5160 ± 20 kJ/mol.2 The theoretical enthalpy of combustion of solid naphthalene was calculated to be -6862.68 kJ/mol using bond energies for the gaseous molecules, the heat of vaporization of liquid water and the literature value of the heat of sublimation of naphthalene, which was 72 ± 4 kJ/mol.2 The absolute value of the difference between the theoretical heat of combustion and the literature
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The bomb was then placed in the center of the calorimeter bucket, the electrodes were connected to the top of the bomb and then 2 L of deionized water was poured into the bucket so that the bomb was completely immersed. The variations in the temperature of this water would be measured and used to calculate the heat capacity of the calorimeter in the benzoic acid run or the heat of combustion in the naphthalene run. The calorimeter lid was then used to cover the calorimeter, while making sure that the stirrer would be able to rotate freely. The bomb calorimetry software, which would record the temperature of the water in the calorimeter, was opened and a new run was started. Once a slow, linear temperature change was observed, the room was cleared of people, and the calorimeter was ignited for five seconds. After another 30 seconds, the room was reentered and the run was stopped once the change in temperature became very small, which took about 15 minutes. The bomb was depressurized, then cleaned using acetone and the calorimeter bucket was emptied and the remaining fuse wire was massed. A pellet of naphthalene was formed using the pellet press and then massed along with a new fuse wire. The entire process that was used for the combustion of benzoic acid was repeated for the naphthalene sample.
Results and Discussion: The heat of combustion of naphthalene was experimentally calculated to be -5025.46 ± 78.98 kJ/mol and