TYPE OF BOND ENERGY REQUIRED TO BREAK THE BOND(j)
C – H 410
C - O 360
O - H 510
O = O 496
C = O 740
C - C 350
To separate C-H bond you need to apply 410 joules of energy. There are five such bonds in ethanol so you multiply 410 by five to get 2050 joules. You do these calculations for all the other types of bonds that make up ethanol, add them all together and you get 3270 joules. All of the other alcohol’s can be broken up in this way.
Methanol
CH3OH + 1.5O2 → CO2 + 2H20
Bonds Broken (C-H) x 3 435 x 3
(O-H) x 1 464 x 1
(C-O) x 1 358 x 1
(O-O) x 1 497 x 1.5
=2872.5kJ mol-1
Bonds Made (C=O) x 2 802 x 2
(O-H) x 4 464 x 4
=3462kJ mol-1
Total Energy Released: 589.5kJ mol-1
Ethanol
CH3CH2OH + 3O2 → 2CO2 + 3H2O
Bonds Broken (C-H) x 5 435 x 5
(O-H) x 1 464 x 1
(C-O) x 1 358 x 1
(O-O) x 3 497 x 3
(C-C) x 1 347 x 1
= 4835kJ mol-1
Bonds Made (C=O) x 4 802 x 4
(O-H) x 6 464 x 6
=5996kJ mol-1
Total Energy Released: 1161kJ mol-1
Propanol
CH3CH2CH2OH + 4.5O2 → 3CO2 + 4H2O
Bonds Broken (C-H) x 7 435 x 7
(O-H) x 1 464 x 1
(C-O) x 1 358 x 1
(O-O) x 4.5 497 x 4.5
(C-C) x 2 347 x 2
= 6797.5kJ mol-1
Bonds Made (C=O) x 6 802 x 6
(O-H) x 8 464 x 8
=8530kJ mol-1
Total Energy Released: 1732.5kJ mol-1
Pentanol
CH3CH2CH2CH2CH2OH + 7.5O2 → 5CO2 + 6H2O
Bonds Broken (C-H) x 11 435 x 11
(O-H) x 1 464 x 1
(C-O) x 1 358 x 1
(O-O) x 7.5 497 x 7.5
(C-C) x 4 347 x 4
= 10722.5kJ mol-1
Bonds Made (C=O) x 10 802 x 10
(O-H) x 12 464 x 12
=13598kJ mol-1
Total Energy Released: 2875.5kJ mol-1
As you can see a longer molecule takes more energy to break its bonds, in this case Pentanol. Compared to a smaller molecule, methanol which requires less energy to do so and Pentanol produces more energy too. I can come to predict that the longer the molecular structure in the alcohol the more energy it will take to remove the bonds. So I think say that pentanol will evolve more energy than methanol simply because it has more bonds to break.
Also using the hypothesis that shows the energy released, I can make a graph to show the energy released compared to the number of carbons in the Alcohol.
Trial Run
We needed to have a trail run so we could remove errors and improve the experiment. We placed the Copper beaker at different heights above the flame of the spirit burner to test which height would be best too use.
In the end we decided it would be best to put the copper beaker 2.5cm above the spirit burner as the further away the copper beaker was put, the longer it would take to heat the water inside and the more alcohol would be needed to raise the temperature of the water.
We also found that during the trial run, the constant moving of people within the room would often move the flame from side to side around the copper beaker which meant the flame was not constantly heating the water in the copper beaker directly. To fix this, we added draft protectors around the spirit burner so the flame was not blown from side to side and this made our results much more reliable as in every result recorded we could see the closeness in all but without the draft protectors the range of alcohol burned was much bigger.
Now the trial run is over and can put together a list of equipment, including draft protectors, that will be needed for the real experiment.
Equipment
Alcohol Burner
Thermometer
Measuring cylinder
Copper Beaker
Water
Heat mat (As Draft Protector)
Mass Balance
Method
- Measure 100cm of water in to a copper beaker.
- Place the beaker into the grasp of the clamp stand.
- Record the starting temperature of the water (Usually 16ºC)
- Weigh the spirit burner with the lid off.
- Put the chosen alcohol burner under the beaker allowing the flame to just touch the beaker. I will be placing the beaker 2.5cm above the spirit burner’s wick.
- Leave the water to heat up until the temperature of the water is exactly 60ºC.
- Weigh the spirit burner new weight
- Record all results.
The variables that must remain constant throughout the experiment
- Mass of the water 100cm
- Type of beaker, Copper
- Temperature of the water will start from 18ºC and the experiment will end when its 60ºC always.
- Room Temperature will stay at 23ºC
- The height of the beaker from the wick (2.5cm)
- Same set of scales
- Weigh the spirit burner with the lid off.
The only variable that must be changed will be the type of alcohol used.
Conclusion
The results of my Experiment are on the next sheet.
The results show that 2.13grams of Methanol were used to heat 100ml of water in a copper beaker. 1.66g of Ethanol was used in average with the first results being due to a mistake made. 1.31g of Propanol was used in average to heat the 100ml of water and 1.07g of Pentanol was used in average.
My hypothesis was that the more carbon atoms in an alcohol, the more energy is required to burn that alcohol and the more energy required to burn the alcohol, the more energy is released by the alcohol in the way of heat, and that heat would be used to heat the water up. That means the more carbons in an alcohol, the more energy it would release as heat and the less of the alcohol is required to be burnt to heat the water up to 60 Degrees.
The results show that more Methanol was needed than any other alcohol to heat water up to 60 degrees, and Methanol has the least amount of carbons. Meanwhile, Pentanol has the most amount of Carbons and less of it was required to heat the water up to 60 Degrees which is what I said in my hypothesis.
Evaluation
During the trial run we had a few problems but before we started the real test, the problems were fixed. In the Trail run the main problem was the draft caused by people moving around the experiments. This movement cause the Flame to change from side to side and the flame was never directly under the copper beaker for the full test. This meant the heating of the water would have been longer and more alcohol would have been needed to heat the water fully. We fixed this by adding draft protectors around the Spirit burner so the flame was not moved by drafts. This made the flame stay in its position and heat the copper beaker in the same place through out the experiment.
We decided not to weigh the spirit burner with its lid on as the lids weight would vary and they could easily get mixed up with another spirit burner. So we avoided using the spirit burner lids.
During the experiment, we would heat the water in a copper beaker, then when it was 60 Degrees , we would weigh the spirit burner and would empty and fill the copper beaker with water.
Firstly, when the spirit burner was weighed the number on the weighing scale would flicker from number to number and would not stop so a number would be picked at random, this meant the results could not be fully accurate and the results average would be different to what it should have been.
When the beaker was emptied, we would have to cool down the beaker so the new water would not have an advantage by being in an already warm beaker, so we would wash the beaker. This would mean making the beaker colder now and making it take a bit longer for the flame to heat up the “just cooled down” beaker with water still on the sides and on the bottom of the beaker. This would have meant more alcohol was used to heat the water than was really needed.
During the emptying of the beaker, we would take the beaker out of the grasp on the clamp and then later put it back in again. During the experiment we never checked to see if the beaker was still the same height over the spirit burner flame as it had been from the start and this could have been an advantage to any alcohols that’s flame was closer to the beaker. I think this may have happened in my first Ethanol experiment where the amount of alcohol used was unusually low.
If we repeated the experiment I would change all the problems but this would need much more time an effort. New beakers would be required and not the one used in the last experiment and the distance of the beaker above the flame would need to be checked. Also more alcohols and more tests would be needed to get a more accurate average and answer.
