In my chemistry coursework I will be investigating the amount of thermal energy different fuels will provide when burnt. My project brief is to “Examine alternative fuels for a power station that has until recently burnt coal. The fuel that gives the best value for money ratio will be the next one used in the power station.”
The costs of the fuels are:
Fuel Cost in £ per kg.
Bond Energy Calculations
The bond energy of a molecule is the energy released after it has reached the ‘barrier’ – the input energy needed for the bonds to break. Different bonds release different amounts of energy. The bond energy of all the fuels listed above needs to be calculated so that I can work out how much heat energy each fuel should theoretically produce when burnt, and then apply it to a formula to work out how cost effective that particular fuel is.
Working out KJ/£
£5.10 per kg
=0.00510 per gram
= 3,296.08 KJ/£
£7.20 per kg
=0.00720 per gram
= 3,126.39 KJ/£
£7.10 per kg
=0.00710 per gram
= 3601.41 KJ/£
£6.20 per kg
=0.00620 per gram
= 4,370.97 KJ/£
From my KJ/£ equations the fuel that I predict would provide most value for money is ‘Butan-1-ol.’ This is because of its relatively low price when compared to the other fuels. Buntanol is the fourth largest molecule - and as such it provides more energy (27.10 KJ/g) and at the lowest price (£6.10) than any of the others specified.
To measure the energy expelled by each of the fuels, the following formula was used:
Mass x Specific Heat Capacity X Temperature Rise = Heat Energy Gained
(kg) (J/KgoC) (oC) (J)
Specific heat capacity is the measure of the required to raise the of a specific quantity of a substance by one Kelvin. A is a unit increment of and is equal to an increment of one degree .
Energy is a difficult variable to measure, and it can never be taken as 100% accurate, as there will be some form of energy loss in any activity. To measure the exothermic energy supplied by burning each of the fuels above, a container of water will be placed close to the flame of the fuel. A temperature change will be measured and then the fuel will be weighed to find how much fuel has been used to produce the change in water temperature. The least amount of fuel used to produce the same temperature change will be the most effective energy transferring fuel – this will be compared to the price to work out how cost effective it is.
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The material the container is made out of will central to my preliminary work, as a more conductive material will raise the temperature of the water to a higher degree than a less conductive object. Other control variables are: The height of the fuel wick, the length between the wick and the beaker, whether the container will have a lid on and any insulation (if required.)
Container (Copper, Aluminium, Coated Black Aluminium)
Heat Resistant Mat
Lid for Container.
Set up the equipment as shown in the diagram
- Weigh each chosen alcohol on scales.
- Measure 50cm of water into a chosen beaker. (Making sure the meniscus is directly on 50)
- Change the length of the wick to 1.5cm above the alcohol.
- Clamp the beaker 3cm above the alcohol.
- Measure the starting temperature of the water, and record.
- Light the wick, and measure the temperature of the water until it raises 30 oC.
- Put out the wick and weigh the alcohol. Record the mass loss of each alcohol.
- Repeat the experiment 3 times per fuel.
- Change the alcohol, and repeat the previous methods.
My first sets of preliminary results were tested using a Bunsen burner, a 2cm wick, 4cm gap between the wick and the container and without a lid. The container was heated on a roaring blue flame for 30 seconds and the start and finish temperatures were measured. The thermometer was at first allowed to rest at the bottom of the beaker, but this would measure the temperature of the container, and not the water, so it was held by hand.
We found these results quite different to the ones that were expected, with the difference between the copper and black aluminium containers as the same. This was put down to the Bunsen burner; the amount of gas that it used was not constant, and as such it could not be relied upon to produce suitable results. This was countered by using Methanol fuel in the next set of results.
The second set of preliminary results were taken with a 1.5cm
Wick and a 3cm gap, with a lid on top of the containers. The thermometer was held in place with a clamp and some insulation was provided in the form of 3 heatproof mats, to keep the flame from flickering and diverting some of the heat energy elsewhere. The object was to heat 50ml of water up by 30 oC and measure the starting and finishing masses of the methanol container. This method was superior to the other, with only two anomalies (highlighted in red.) The anomalous results were then retested. The results we gathered were all within a 5% error margin.
Retested results: Black Aluminium and Copper
These results have been put back into the table, with the averages added on.
Results from the table show that normal aluminium is the best conductor, with the lowest amount of fuel used to heat the water by 30 oC. This will then be the container used in the real experiment,
Fair Testing & Accuracy
All of the preliminary work was done to a high standard and this was reflected in our results. As many variables as possible had been controlled. The lid on the container seemed to have an increased effect in keeping in heat, so this will be necessary in the real tests. Insulation around the fuel and beakers helps to keep most of the heat directed towards the beaker. Wick length is best kept short, as a long wick makes the flame flicker wildly, which does not direct all of the heat towards the container. The length between the wick and the beaker is kept short for the same reason. The cap was also put back onto the fuel container to stop small amounts (0.01g) evaporating, because this would inevitably affect our results.
Final Results Table
Anomalies are highlighted in red, and a repeat was done to judge weather it was just human error, or a misjudgement in the experiment kit.
Methanol – 5% error margin
Ethanol – 6% error margin
Propan-1-ol - - 6 % error margin
Butan-1-ol - 6% error margin
Pentan-1-ol - 5% error margin
We have found that Pentan-1-ol did not use less fuel than butan-1-ol. This may have been due to incomplete combustion between pentan-1-ol and the oxygen it reacted with.
My prediction was that Butan-1-ol’ would provide the best value for money. This was because of its relatively low price when compared to the other fuels. Buntan-1-ol is the fourth largest molecule - and as such it provides more energy (27.10 KJ/g) and at the lowest price (£6.10) than any of the others specified. This can be seen in a cost comparison of the fuels, in £/Kg, using the average mass burnt of each fuel.
The graph below shows the average mass of fuel used to raise the temperature of the water by 30 ̊ C. The table of results shows that Butan-1-ol required the least fuel. This goes against the prediction that pentan-1-ol would require the least fuel to heat the water, and propan-1-ol requiring the second smallest. The reason why Pentan-1-ol may have used more fuel may be down to incomplete combustion between the fuel and oxygen. This is why it is shown as an anomalous result on the graph. Further proof of this was black soot on the bottom of the test beakers. Methanol, being one of the cheapest fuels to buy, may contain certain impurities that the other more expensive fuels would not have in them.
KJ/£ - Real results
Mass x Specific Heat Capacity X Temperature Rise = Heat Energy Gained
(kg) (J/KgoC) (oC) (J)
(50 x 4.2 x 30 = 6300 J or 6.3 KJ.)
= 7.5 KJ/g
= 1476.59 KJ/£
= 10 KJ/g
= 1388.89 KJ/£
= 12.35 KJ/g
= 1739.44 KJ/£
= 14 KJ/g
= 2258.06 KJ/£
I have now drawn both my theoretical and actual results onto a bar chart to show any relationships between the two. I can clearly see that the actual results are about half of what they theoretically should be. This is because there is a large amount of heat loss around the water, and the energy from the fuel is not only transferred as heat, but also light, so there will never be 100% efficiency. It also shows that as expected, butan-1-ol is the best value for money, therefore proving my original prediction. The flickering of the fuel’s flame may have also caused some heat loss. Black soot was also observed on most of the beakers at the end of each experiment, this may mean that each fuel did not combust to a certain extent, as there may have been a slight lack of oxygen required for it to combust correctly. Although these figures are below what would have been expected, they still show the same trend pattern that the theoretical values dictate, as further explained by the graph below.
From the results in this line graph we can clearly see the link between the theoretical and actual readings, the two show the same trends, (the peaks and troughs) just on a lower scale for the actual results. These results are very consistent and this helps to prove that our results are reliable - to suggest that Butan-1-ol will be the most cost efficient fuel for Max Profit to use in his power station.
Throughout my study I have maintained a high level of accuracy – in the fairness of the experiments - to the consistency of the results, as all fall within a 10% error margin, with the majority below 5%. Most of the anomalies found were due to either human error in reading the thermometer, or measuring the water. The cap on the fuel improved the accuracy of the tests, by not letting small amounts of the fuel evaporate. These anomalies were then retested, and more suitable results were obtained.
Both lines of the graph have a similar shape which indicates that they are accurate. Also I can work out the percentage of energy per mole I got into the water out of the energy I predicted to get. This can be done by dividing the energy I got by the predicted values then multiply by a 100. This gives me
The actual results are about half of what has been predicted by using the bond equations. The main factor which has affected the results here has been the heat loss from the fuel flame into the surroundings. The results are also consistent to this theory. I believe that the accuracy of my experiments and of my investigation gives proof that – as in my hypothesis - Butan-1-ol should be chosen as the new fuel for the power station.
Most of the method worked accurately, but to increase this, I would have used a top pan balance to measure the volume of water needed, as this would have taken away the chance of leaving drops in the bottom of the measuring tube. Electronic ‘nodes’ to measure accurately the temperature of water could have been utilised in making Temperature/Time graphs, to show the gradient with different fuels. This could have added a greater depth to my investigation as I could accurately measure the temperature change over a certain time, and see which fuel would raise the temperature of the water the fastest. Problems such as the incomplete combustion and flickering flames could be solved by building an insulation chamber, made from heat-reflecting materials to direct as much heat as possible onto the beaker. Pure oxygen would also be pumped in, to allow the fuel to combust as fully as possible. This may not be possible in the real power station, so incomplete combustion would play a part in the daily routine of the station, possibly increasing the running costs.
Here's what a star student thought of this essay
Quality of writing
The authorÃ¢â‚¬â„¢s spelling and grammar is very good throughout, and they have presented their report well with clear sections with sensible headings. They have made good use of tables and graphs to display their results, and used very good scientific vocabulary throughout. However, at times they donÃ¢â‚¬â„¢t appear to quite understand this, for example they said Ã¢â‚¬Å“To measure the exothermic energy supplied by burning each of the fuels aboveÃ¢â‚¬Â when they were measuring the thermal energy released by the combustion of each fuel. However, for the most part they have shown a very good knowledge of chemistry and how to present their work well.
Level of analysis
The author began their investigation by using bond enthalpy values to predict the cost per KJ of energy released by burning each fuel. Although they have not quite appeared to understand the definition of bond enthalpies, saying Ã¢â‚¬Å“The bond energy of a molecule is the energy released after it has reached the Ã¢â‚¬ËœbarrierÃ¢â‚¬â„¢ Ã¢â‚¬â€œ the input energy needed for the bonds to breakÃ¢â‚¬Â, when a better definition would have been the energy required to break a particular bond in a gaseous molecule. It is also unclear where these values came from, as they do not match the values for the enthalpy of combustion in my data booklet. I would have quoted the enthalpy of combustion values from the data booklet, then converted these from KJ/mol to KJ/kg, and finally calculated the cost per KJ of energy produced (or the number of KJ per pound). This just makes it much clearer to the examiner how you got the values, as well as showing some mathematical ability. After predicting which fuel would be best, the author carried out the experiment. They did similar calculations to calculate how cost effective each fuel was, and compared their results to the predicted results, calculating the percentage yield. Although they have identified some anomalies in their data, I would have shown how I calculated that these were anomalies, using: anomalies > mean + 0.5 x interquartile range or < mean Ã¢â‚¬â€œ interquartile range. This just tells the examiner exactly what you are doing so he can give you more marks for it! Occasionally, the author doesnÃ¢â‚¬â„¢t explain things very clearly, for example I would have explained the purpose of the preliminary experiment at the beginning of that section, rather than at the end, which makes the report much easier to follow. They have also occasionally said things such as Ã¢â‚¬Å“the prediction that pentan-1-ol would require the least fuel to heat the waterÃ¢â‚¬Â without explaining where this came from, which could easily confuse the reader.
Response to question
The author has successfully carried out an experiment to choose a fuel for a power station which would be the most cost-effective. They have calculated the percentage yield of each of the fuels, and used bond enthalpy values to predict the best fuel, and used this information alongside their experiment to come to a well reasoned conclusion, and considered sources of uncertainties in their experiment, as well as suggesting improvements.