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Burning Fuels Coursework

Extracts from this document...

Introduction

10/10/06 Chemistry Coursework 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. Methanol 5.10 Ethanol 7.20 Propan-1-ol 7.10 Butan-1-ol 6.20 Pentan-1-ol 16.90 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/� Methanol 16.81 KJ/g �5.10 per kg =0.00510 per gram 16.81 0.00510 = 3,296.08 KJ/� Ethanol 22.51 KJ/g �7.20 per kg =0.00720 per gram 22.51 0.00720 = 3,126.39 KJ/� Propan-1-ol 25.57 KJ/g �7.10 per kg =0.00710 per gram 25.57 0.00710 = 3601.41 KJ/� Butan-1-ol 27.10 KJ/g �6.20 per kg =0.00620 per gram 27.10 0.00620 = 4,370.97 KJ/� From my KJ/� equations the fuel that I predict would provide most value for money is 'Butan-1-ol.' ...read more.

Middle

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 Fuel 1st Result 2nd Result 3rd Result Anomalous Repeat Average Methanol Start Mass (g) 130.45 129.56 128.68 Finish Mass (g) 129.62 128.71 127.85 Mass Used (g) 0.83 0.85 0.83 0.84 (2 d.p.) Ethanol Start Mass (g) 156.53 155.91 155.19 154.08 Finish Mass (g) 155.92 155.22 154.56 153.44 Mass Used (g) 0.61 0.69 0.63 0.64 0.63 (2 d.p.) Propan-1-ol Start Mass (g) 182.39 181.86 181.31 180.84 Finish Mass (g) 181.89 181.32 180.86 180.34 Mass Used (g) 0.50 0.54 0.45 0.50 0.51 (2 d.p.) Butan-1-ol Start Mass (g) 182.84 182.40 181.90 Finish Mass (g) 182.41 181.92 181.46 Mass Used (g) ...read more.

Conclusion

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. ...read more.

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Response to the 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 ...

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Response to the 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.

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 “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”, 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 – interquartile range. This just tells the examiner exactly what you are doing so he can give you more marks for it! Occasionally, the author doesn’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 “the prediction that pentan-1-ol would require the least fuel to heat the water” without explaining where this came from, which could easily confuse the reader.

Quality of writing

The author’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 don’t appear to quite understand this, for example they said “To measure the exothermic energy supplied by burning each of the fuels above” 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.


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