Question

Post lab question reguarding bomb calorimetry:

Heat capacity for calorimeter: 10403.64 J/◦C

Delta H TTCC: -6864.20 kJ/mol

Resonance energy benzene: 423.01 kJ/mol

ΔE = -7096.54kJ/mol

1. How does the bomb get sealed when it is charged with oxygen gas?

2. Why is 1 mL of water added to the bomb before the oxygen gas is added? Would one drop (0.05 mL) of water be satisfactory?

3. Is the mechanical energy of the stirrer included in the heat capacity of the calorimeter? Explain your reasoning.

4. How does the ignition system work to cause combustion? Why doesn't the circuit "short out" because of the water in the bucket?

5. What happens to the wire when it combusts? Write a chemical equation for the reaction that occurs.

6. Does the ΔH combustion you calculate correspond to the initial temperature, the final temperature, or some other temperature? Why?

7. The temperature immediately after a sample is combusted in the bomb can be as much as 1500ΕC or more. Why don't you use this temperature in any of the calculations?

8. Heats of combustion listed in the various texts and handbooks are standard heats of combustion. Your determination was not carried out under standard conditions. Will this have any effect as you compare your enthalpies with the literature values? Explain your reasoning. (See Noggle, Physical Chemistry, 2nd edition, Scott Forseman, 1989, p. 90)

9. Combine your experimentally determined ΔHΕ combustion value for TTCC with standard heats of formation from the literature for CO2(g) and H2O(Ρ) to determine the standard heat of formation of 1,5,9,-trans-,trans-,cis-cyclododecatriene.

Answer 1

1. The bomb vessel after charging with oxygen gas is placed inside the calorimeter, then the lid is closed. The bomb vessel is now isolated from outside temperature variations. As soon as the bomb vessel temperature has stabilised in the bomb well, the sample is then ignited.

2. In a reaction, the quantity of heat that raises the temperature of some substances by some amount, the same amount of heat can simultaneously raises the same temperature of certain mass of water.The mass of the water is then termed as water equivalent which is calculated.