Table of data
- Table to show energy differences between preceding alcohols
Data Processing
- Calculations
- Energy liberated for each alcohol (J)
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Formula: m.c.Δt
- Ethanol: 158.54 x 4.18 x (32-20) = 7952.37
- Propanol: 158.04 x 4.18 x (34-21) = 8587.89
- Butanol: 159.18 x 4.18 x (34-22) = 7984.47
- Pentanol: 159.32 x 4.18 x (33-21) = 7991.49
- Hexanol: 158.37 x 4.18 x (34-21) = 8605.83
- Heptanol: 158.03 x 4.18 x (35-20) = 9908.48
- Octanol: 159.54 x 4.18 x (39-22) = 11336.91
- Nonanol: 159.67 x 4.18 x (31-20) = 7341.63
- Molar mass of each alcohol (g)
- Ethanol: C2H5OH (12x2)+6+16 = 46
- Propanol: C3H7OH (12x3)+8+16 = 60
- Butanol: C4H9OH (12x4)+10+16 = 74
- Pentanol: C5H11OH (12x5)+12+16 = 88
- Hexanol: C6H13OH (12x6)+14+16 = 102
- Heptanol: C7H15OH (12x7)+16+16 = 116
- Octanol: C8H17OH (12x8)+18+16 = 130
- Nonanol: C9H19OH (12x9)+20+16 = 144
- Molar Enthalpies of combustions (kJ/Mol^-1)
- Ethanol: 7952.37 for 0.32g ethanol
- Molar Mass = 46g
- 7952.37 x 46/0.32 = 1,143,153.19 J/Mol^-1
- = 1,143.15 kJ/Mol^-1
- Propanol: 8587.89 for 0.33g propanol
- Molar Mass = 60g
- 8587.89 x 60/0.33 = 1,561.43
- Butanol: 7984.47 for 0.28g butanol
- Molar Mass = 74g
- 7984.47 x 74/0.28 = 2,110.18
- Pentanol: 7991.49 for 0.32g pentanol
- Molar Mass = 88g
- 7991.49 x 88/0.32 = 2,197.66
- Hexanol: 8605.83 for 0.32g hexanol
- Molar Mass = 102g
- 8605.83 x 102/0.32 = 2,743.11
- Heptanol: 9908.48 for 0.38g heptanol
- Molar Mass = 116g
- 9908.48 x 116/0.38 = 3,024.69
- Octanol: 11336.91 for 0.35g octanol
- Molar Mass = 130g
- 11336.91 x 130/0.35 = 4,210.85
- Nonanol: 7341.63 for 0.19g
- Molar Mass = 144g
- 7341.63 x 144/0.19 = 5,564.18
Balanced equation for the combustion of ethanol
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C2H5OH(l ) + 302(g) → 2C02(g) + 3H20(l )
Balanced equation for the combustion of propanol
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2C3H7OH(l ) + 9O2(g) → 6C02(g) + 8H20(l )
General equation for the combustion of alcohols
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Alcohol + Oxygen → Carbon-Dioxide + Water
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CnH2n+1 + 02 → C02 + H20
- Conclusion and Evaluation
- According to my graph, the heat combustion increases as the molar mass increases, for both the literature values, and the values obtained from my experiment. My graph shows one straight-line (Literature values), and another somewhat straight-line (experimental values), and this shows that the more carbon atoms there are in a compound, the heat of combustion goes up. This is probably because the molecular length of the compound increases, increasing the surface area, thus allowing more energy to be released, and also because every time you add another carbon atom, you are adding 15 onto the Relative Atomic Mass. The molar mass increases by 14g with each CH2 group. The literature values of the molar enthalpies of combustion generally increased by approximately 654 kJ/Mol^-1 with each CH2 group. However, there was no general pattern for the increase of the molar enthalpies of combustion with each CH2 group for my experimental values, which were a bit scattered, and which also limits my conclusion because the relationship is not clear.
- With each CH2 group, the energy liberated does increase, but definitely not with a constant. The increasing values obtained from my results show no general pattern.
- My experimental values compared to the literature values are a bit inaccurate, with them being only 76.61% correct, on average. I think the principal sources of error in this experiment were the slight differences in some of the variables, and the loss of heat to the surroundings. The room temperature might have acted as a cooling agent, the calorimeter being copper means that it loses heat as easily as it gains heat, so there is a possibility that not all the heat would be transferred as the water heats up. Also, the clamp was metal, so some of the heat might have been transferred to the clamp and stand, and thus, lost during the experiment.
- Other weaknesses during this experiment could be the measuring of certain variables. The mass of the water inside the calorimeter might not have been 80 cm cubed, due to incorrect reading caused by the error parallax. Also, the flame was not always touching the calorimeter, so this would have caused differences in the amount of heat given off. Another weakness was that the amount of wick on the spirit burner was not the same on each burner, and the calorimeters had varying amounts of alcohol in them, so this would have caused differences in the amount of alcohol burnt. Lastly, although we used the digital thermometer, and were stirring the water to get the temperature, there would still be differences in the temperature of the water at different depths, and this would affect our results.
- In conclusion, to get slightly more accurate results, I would measure the wick length and height of calorimeter above the flame for each trial, I would make sure that each calorimeter has the same amount of alcohol in it, and I would also insulate the clamps and try other conductors to heat besides water. It might also help to take more readings so that the data is more consistent.