Calculations.
Methanol- 2CH4O + 3O2 ,→ 2CO2 + 4H2O
Bonds Broken.
C-H x 6 = 2478
H-O x 2 = 928
O=O x 3 = 1494.4
C-O x 2 = 672
= 5572.9
Bonds Made.
C=O x 4 = 3220
H=O x 8 = 3712
= 6932
Total Energy Release = 6932 – 5573 = 1359 kJ/mole
(1359 ÷ 2) ÷ 32 = 21.2 kJ/mole
Ethanol- C2H5OH + 3O2 → 2CO2 + 3H2O
Bonds Broken.
C-H X 5 = 2065
H-O X 1 = 464
O=O X 3 = 1495
C-O X 1 = 358
C-C X 1 = 347
= 4729
Bonds Made.
C=O x 4 = 3220
H=O x 6 = 2784
= 6004
Total energy Release = 1275 ÷ 46 = 28kJ/ mole
Propanol – 2C3H7OH + 9O2 → 6CO2 + 8H2O
Breaking Bonds.
C-H x 7 = 2891
C-O x 1 = 358
C-C x 2 = 694
O-H x 1 = 464
O=O x 9 = 4484.7
=8891.7
Making Bonds.
H=O x 16 = 7424
C=O x 12 = 9660
= 17084
Total Energy Release =(17804 – 8891.7) ÷ 2 = 4096.15 kJ/mole
4096.15 ÷ 60 = 68.3 kJ/ g
Butanol, - C4H9OH + 6O2 → 4CO2 + 5H2O
Breaking Bonds.
C-H X 9 = 3717
C-O X 1 = 358
C-C X 3 = 1041
O-H X 1 = 464
O=O X 6 = 2989
= 8569
Making Bonds.
H=O X 10 = 4640
C=O X 8 = 6440
= 11080
Total energy Release = 11080 – 8569.8 = 2510.2 kJ/mole
2510.2 ÷74 = 33.9 kJ/g
Pentanol- 2C5H11OH + 15O2 → 10CO2 + 12H2O
Breaking Bonds.
C-H X 11 = 4543
C-O X 1 = 366
C-C X 4 = 1388
O-H X 1 = 464
O=O X 15 = 7474.5
= 14205.5
Making Bonds.
O=H x 24 = 11136
C=O x 20 = 16100
= 27236
Total Energy Release = 27236 – 14205.5 = 13030 ÷ 2 = 6515.25 kJ/ mole
6515.25 ÷ 88 = 74.04 kJ/ g
Conclusion.
According to my experiment Butanol was the most effective fuel, it burned for the longest and produced the most energy (15.262 kJ). This was not as I expected, as in my prediction the most effective fuel was Pentanol. The rest of the fuels fit the pattern of my prediction.
The reason for this could be because the alcohols with more carbon atoms burnt more fuel so there would be less energy per gram, as more fuel has been burnt. More fuel has been burnt because of the large number of carbon atoms and large molecular length, therefore the greater surface area is allowing more energy to be released.
My final results were much lower than I predicted. This is because not all energy is used to heat the water. Some energy is lost through light, and also some heat is used to heat the can. Also the chemical reaction was not exactly as in my prediction, there was some left over products (mostly carbon).
My prediction of the more chemical bonds to be broken the longer fuel burned was mainly correct. Although there was no strict pattern to the time taken, it did gradually rise as the number of bonds in the fuel became greater.
Evaluation
Although I had no anomalous results, my final results were much lower than I predicted. The difference between each fuel was also much less than I thought. There are many reasons for this, but I think the main reason is energy loss.
I do not think that my results were very accurate. I think this because ;
- Not all energy was used to heat the water- some was used as light, and some energy was used to heat the can.
- Some water may have evaporated, therefore there was less water meaning less energy is needed to heat it.
- Not all the water started at the same temperature.
- I did not use enough fuels.
The equipment used in the experiment has affected my results, as some heat was lost heating the can. Also some heat is transferred into the stand and clamp.
As some of the water evaporated there was less water to be heated. This meant that my results would not all have been for the same mass of water.
If I redid my experiment I would include more fuels (such as hexanol). I would also try and reduce the energy loss in my experiment, as this was the main reason for my results being inaccurate. I could do this by measuring what energy is lost eg. Light and Heat used to heat the air and can. I could also try and reduce energy loss by placing the can closer to the flame.
