Number and types of bond for the left hand side of the equation.
C-H = 3 x 413 = 1239
C-O = 1 x 358 =358
O-H = 1 x 464 = 464
O=O = 1.5 x 498 = 747
Total = 2808 KJ
Number and types of bond for the right hand side of the equation.
C=O = 2 x 805 = 1610
O-H = 4 x 464 =1856
Total = 3466
Overall energy change = 3466-2808
= 658 KJ
Energy transferred = 100 x 4.2 x 52
= 21840 KJ for 2.8g of ethanol.
Energy transferred for 1g of Ethanol = 21840
2.8
= 7800 J/1g Ethanol
= 7800
1000
= 7.8 KJ/1g of Ethanol
The table below shows the amount of energy transferred by 1g of ethanol at each temperature:
As you can see from the table above the amount of energy being transferred increases as time goes on. However, this is not a very accurate experiment because the results show that 2 minutes is not long enough to see the reaction fairly and accurately. So I decided to extend the time to 5 minutes, so that I can observe the amount of energy being transferred to the water in a longer time period. Due to extending the time allowed per experiment I decided to double the amount of water in the copper container as the temperatures of the water were quite high in just the space of two minutes.
Variables
The amount of energy transferred to the water may be affected by a number of factors, such as the amount of alcohol in the spirit burner, the material of the container, the type of alcohol, the size of the molecule, the number of bonds the molecule has, or the time the fuel is burned. All of these factors may affect the amount of energy transferred to the water, for instance the size of the molecules in the alcohol may affect the amount of energy transferred because the larger the molecule the more energy is needed to break the bonds in the alcohol. The same principle applies to the different types of alcohols, because as you go down the homologous series of alcohols you find that as you down the series the molecular structure contains more carbon atoms than the alcohol before it in the series. (eg. Ethanol C2, Propanol C3). Due to this extra carbon in the alcohols structure it requires more energy to break the bond in the alcohols. The time the fuel is burnt also might affect the amount of energy transferred, because the longer the fuel is kept burning the more energy is transferred as there is more of a time space which allows more energy to be produced as more bonds are being broken, compared to if you left the alcohol burning for a short time (1 minute), that wouldn’t be enough time for the alcohol to produce sufficient energy.
Measurement
I am going to measure the time taken in seconds and I am going to measure the temperature of the water in °C. I am also going to measure the amount of energy transferred into the water in KJ. I am going to record the mass of the alcohol in grams.
Prediction
I predict that the amount of energy transferred to the water will increase as time goes on, as the amount of energy transferred to the water will added to as more bonds are broken, and if the temperature of the water is below 100°C then very little energy will be lost through heat. I predict that alcohols further down in the homologous series (butanol) will transfer more energy because the molecular structure contains more carbon atoms than the alcohol before it in the series. Due to this extra carbon in the alcohols structure it requires more energy to break the bond in the alcohols, so therefore more energy will be transferred to the water. Also energy is given out when the atoms from the alcohols and oxygen join together to the product:
More CO2 x H2O = more energy released.
Method
Equipment:
- Spirit Burner
- 4 Alcohols (Methanol, Ethanol, Propanol, and Butanol)
- Retort stand and clamp
- Copper container
- Thermometer
- 200 ml of cold water
- Stop Watch
- Balances
- Heat resistance mat
The first thing you should do before even setting up the equipment is to put on safety goggles as you will be dealing with extremely flammable and potentially dangerous substances. Once you have done that assemble equipment as in diagram above. If the spirit burner is not already set up, fill the spirit with 10 ml of the alcohol. But be careful when pouring in the alcohol into the burner, as it is very flammable, if you spill any onto you wash it off. Then weigh the spirit burner with the fuel and record it. Measure out 200 ml of cold tap and put it into the large copper container and clamp above the spirit burner. Take the temperature of the cold water. Then light the spirit burner and start the stopwatch. Measure the temperature of the water in the copper container every 30 seconds for 5 minutes. After 5 minutes put out the flame, and then measure the burner and record the mass. Repeat this two to three times. Then repeat for each alcohol.
To make this experiment a fair test I repeated the experiment twice times to calculate an average. I also tried to keep all of the other variables the same, such as the material of the container, the time fuel burnt and so on. However, due to external factors I could not control the size of the wick on the fuel burner nor could I control the amount of spirit in the burner, as the alcohols were already prepared in different burner. However, this prevented contamination between two different alcohols, which allowed me to gain more accurate results, as there was no possibility of contamination.
I have used the results tables above to calculate the amount of energy transferred to the water for 1 g of each alcohol tested.
Methanol
C2H5OH + 3O2 2CO2 + 3H2O
Number and types of bonds on the left hand side of the equation:
C-H = 5 x 413 = 2065
C-C = 1 x 347 = 347
C-O = 1 x 358 = 358
O-H = 1 x 464 = 464
O=O = 3 x 498 = 1494
Total = 4728
Number and types of bonds on the right hand side of the equation:
C=O = 4 x 805 = 3220
O-H = 6 x 464 = 2784
Total = 6004
Overall energy change = 6004-4728
= 1276 KJ
Energy Transferred = mass of water x change in temperature x specific heating capacity
Mass difference
Ethanol
CH3OH + 11/2 O2 CO2 + 2H2O
Number and types of bonds on the left hand side of the equation:
C-H = 3 x 413 = 1239
C-O = 1 x 358 = 358
O-H = 1 x 464 = 464
O=O = 1.5 x 498= 747
Total = 2808
Number and types of bonds on the right hand side of the equation:
C=O = 2 x 805 = 1610
O-H = 4 x 464 = 1856
Total = 3466
Overall energy change = 3466-2808
= 658 KJ
Propanol
C3H7OH + 4 ½ O2 3CO2 + 4H2O
Number and types of bonds on the left hand side of the equation:
C-H = 7 x 413 = 2891
C-C = 2 x 347 = 694
C-O = 1 x 358 = 358
O-H = 1 x 464 = 464
O=O = 4 ½ x 498 = 2241
Total =6648
Number and types of bonds on the right hand side of the equation:
C=O = 6 x 805 = 4830
O-H = 8 x 464 = 3712
Total = 8542
Overall energy change = 8542-6648
= 1894 KJ
Butanol
C4H9OH + 6 O2 4CO2 + 5H2O
Number and types of bonds on the left hand side of the equation:
C-H = 9 x 413 = 3717
C-C = 3 x 347 = 1041
C-O = 1 x 358 = 358
O-H = 1 x 464 = 464
O=O = 6 x 498 = 2988
Total =8568
Number and types of bonds on the right hand side of the equation:
C=O = 8 x 805 = 6440
O-H = 10 x 464 = 4640
Total = 11080
Overall energy change = 11080-8568
= 2512 KJ
The table below shows the amount of energy transferred to the water for 1g of fuel for each alcohol:
Analysing the graph you can clearly see that as time goes on the greater the amount of energy is transferred to the water, this is shown by the positive correlation of the graph. There are a few anomalous results in this graph however; this could be down to the fact that I only repeated the experiment twice. The anomalous results however, are subtle and don’t stick out of the graph a great deal.
Analysing the graph you can clearly see that as time goes on the greater the amount of energy is transferred to the water, this is shown by the positive correlation of the graph. There are a few anomalous results in this graph however; this could be down to the fact that I only repeated the experiment twice. The anomalous results aren’t as shuttle as in the last graph, but that may be down to the amount of alcohol in the container. After the first experiment the spirit burner had lost 3.83g of Methanol, compared to only losing 1g in the Ethanol tests, so that could have affected the results so that may be why the anomalous results aren’t as subtle as they were in the experiment with Ethanol.
This graph also shows a positive correlation and corresponds with the other graphs in showing that the greater the time the greater the amount of energy is transferred to the water. However, unlike the other graphs it only has one subtle anomalous result. This could be due to the difference in mass of the fuel of 0.1g that is probably why it is subtler than the anomalous results in the Methanol graph.
This graph shows what the graphs have shown, however, the positive correlation isn’t as strong as in the other graphs. The graph shows a steady increase in the amount of energy transferred, until 270 seconds into the experiment where there is a sudden surge of energy transferred then the energy level decreases dramatically. This could be another anomalous result, however, it could also mean that Butanol has reached its optimum energy level so the energy is lost rather than being added to.
This graph shows that Methanol transferred the most energy, but that may be due to the size of the wick on the spirit burner. Methanol had the largest wick followed by Ethanol, then Butanol, then finally Propanol. So you can’t really say that Butanol transferred the most energy by just looking at this graph.
Analysis
Analysing the first few line graphs graph you can clearly see that as time goes on the greater the amount of energy is transferred to the water, this is shown by the positive correlation of the graph. There are a few anomalous results in the graphs however; this could be down to the fact that I only repeated the experiment twice, or the varying amount of spirit in the spirit burner. However, the butanol graph shows something different from the previous graphs. Butanol contains more carbon atoms than the other alcohols that I tested, even though the graph shows a positive correlation it isn’t as strong as in the other graphs. The graph shows a steady increase in the amount of energy transferred, until 270 seconds into the experiment where there is a sudden surge of energy transferred then the energy level decreases dramatically. This could be another anomalous result, however, it could also mean that Butanol has reached its optimum energy level so the energy is lost rather than being added to. I also noted that Butanol burnt less fuel than the other alcohol, I am not sure whether that is down to the thickness of the wick on the spirit burner, or the fact the butanol has 4 carbon atoms, so it would require more energy to break them, as Carbon atoms are very large, and so have strong bonds between them. This might be able to explain why there is such a sudden surge of energy then such a drop in energy.
Analysing the results of this experiment, you can see that the amount of energy transferred to the water increases as time goes on, which coincides with my prediction. However, the results I gathered to show which alcohol transferred the greatest amount of energy to the water, didn’t not coincide with my prediction, as I predicted that that the alcohol with the greatest amount of carbons in its molecular structure. Instead the graph shows quite the opposite, however, I feel I can’t come to an accurate scientific conclusion based on these results alone. I can’t come to a conclusion with these results as the spirit burners for each alcohol were different and had different wick sizes, which probably affected the results, so all of this has to be taken into account. Due to this important factor I believe that from these results I can’t make a solid scientific conclusion.
There are also quite a few anomalous results that can be seen clearly in the graphs above. These results could be due varying amount of alcohol in the burner, and I only also tested each alcohol twice, maybe if I increased the amount of tests I performed on each alcohol to three times, maybe I would have been able to make a more accurate average.
Evaluation