The Bomb Calorimeter

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Experiment B2, Heats of Combustion – The Bomb Calorimeter.

Objectives:

To calibrate a bomb calorimeter by the combustion of benzoic acid. Then to use the calibrated calorimeter to measure the heat of combustion of naphthalene and calculate the heat of formation of naphthalene.

Theory:

q = C.ΔTBA C = q / ΔTBA

Moles = mass / Mr

ΔŪ = ΔU / moles

ΔHoc,298 = ΔŪoc,298 + PDV = ΔŪoc,298 + RTΔn

C10H8 (s) + 12O2 (g) 10CO2 (g) + 4H2O (l)

ΔHoc,298 = - 1 x ΔHof (Nap) + 10 x ΔHof (CO2) + 4 x ΔHof (H2O)

Procedure:

1. First, a pellet of approximately 1.0g of benzoic acid was weighed out using a four decimal place mass balance and the weight was recorded at 1.0022g recorded.

2. Then approximately 2400cm3 of distilled water was added to the calorimeter. A pipette was used to measure out 10cm3 of distilled water which was immediately added to a clean bomb.

3. The top of the bomb electrode was held so that a length of tungsten wire was passed through the hole in each electrode to connect the two electrodes together, to ensure that the wire was not taut.

4. The wire was then wound around the electrode to ensure a good electrical point contact was made.

5. A length of cotton was then tied around the pellet and then the cotton attached to the tungsten wire and pellet place in the metal crucible below the electrodes.

6. The benzoic acid pellet was engraved on to make it easier to knot the cotton onto it.

7. Teflon tape was then wound around the edge of the lid and then inserted into the bomb and screwed in tightly. The bomb was then filled with oxygen to a pressure of 25 atmospheres.

8. The same steps from 1-8 was repeated for Naptheline.

Results:

|Compound tested |Benzoic acid |Naphthalene | |Mass (g) |1.0022 |0.6497 |

|Time (minutes) |Benzoic acid, temperature (oC) |Naphthalene, temperature (oC) | |0.5 |21.0 |22.7 | |1.0 |21.1 |22.7 | |1.5 |21.0 |22.7 | |2.0 |21.0 |22.7 | |2.5 |21.1 |22.7 | |3.0 |21.1 |22.7 | |3.5 |21.0 |22.7 | |4.0 |21.1 |22.7 | |4.5 |21.1 |22.7 | |5.0 Bomb Fired |21.1 |22.7 | |5.5 |21.5...
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