The above will only calculate approximate values as the formula was devised form the graph which can cause inaccuracies. For example, an alcohol with 15 carbon atoms would produce the following amount of energy with this apparatus: y = x = 15 =3214. 29 kJ/mol to 2 d. p. Hence, using the same method, we can devise a formula with the predicted accurate values. It would be: y = 1217x + 910 The above is accurate and will calculate exactly the amount of energy produced. For example, an alcohol with 15 carbon atoms will produce exactly this amount of energy.
The two formulas are able to support my explanation that energy transfer is not 100 per cent efficient and that a lot of energy is always lost. GCSE Chemistry Coursework Investigation into energy changes in the combustion of alcohols Evaluation The procedure of the experiment did not allow us to obtain highly accurate results because a lot of energy was still lost to the environment, though a draft excluder was used, heat was lost through the top of the apparatus. Hence this explains why our actual results are smaller than the predicted ones because energy is lost and so not all of it is taken into account.
The procedures qualitative errors were a major problem, hence the large difference between the two results, though they show the same trend. The results are fairly accurate to what was actually measured, they differ with the predicted results due to the main qualitative error which was heat loss. Otherwise they are fairly accurate results to what was actually transferred to the water and the can. Also we did not calculate the heat transferred to the can accurately because we assumed its temperature rise was also 20i?? C, which is the same as the water.
This is wrong because heat is not all transferred to the water and instead to the environment, and hence the temperature of the can is actually higher than 20i?? C, and also explains why the actual results were smaller than the predicted. We were only measuring temperature with a thermometer to the nearest degree, this is highly inaccurate because any small error made in these measurements are magnified because we are manipulating the results to get what we want, i. e. the energy transferred. Therefore this reduced the accuracy of the results.
The anomalous results that were below the line of best fit showed that the energy released was too small, this was because of extra heat loss than expected and was caused by us blowing onto the can or water to cool it and also not fully closing the draught excluder. The anomalous results that were above the line of best fit show that the energy released was too high and was due to uneven stirring of the water and so some areas of the water were hotter than the others.
It was also due to the fact that the tip of the flame was too near to the bottom of the can, i. e.height x is too small, and so it was an unfair test and less heat was lost than expected. The procedure was highly inaccurate due to the apparatus used, which caused too much heat to be lost. The apparatus was not in sealed conditions and so a lot of heat was lost to the air around it, between the flame and the can causing convection currents. If the flame was too near the bottom of the can it would mean less heat loss but also incomplete combustion and so the energy transferred would be different than expected and the carbon that forms on the bottom of the can causes inefficient heat transfer.
If the flame was too far form the can then there would be a lot of heat loss and so affecting the accuracy of the results. The draught excluder proved to be of limited use as heat rises and so heat was not kept in from above where most heat energy is lost. The measurements were also not accurate enough as the results would have to manipulated. It is for these reasons that the procedure is not suitable enough to enable us to produce highly accurate results of which would be very similar to the predicted. But we must appreciate the fact that there is never a 100 per cent energy conversion and that energy is always lost.
An improve procedure, would involve the use of a thermocouple to replace this calorimeter. The thermocouple reduces heat loss greatly as it is able to create a sealed environment and so nearly all the energy released in the combustion of the alcohol is accounted for. The water is also circulated and so is heated evenly. But the calorimeter could be improved by heating the water by a larger temperature, such as 60i?? C. This means that the inaccuracy of the thermometer would be spread over a larger temperature and so the error factor is smaller.
We could also use a digital thermometer instead which measure to 2 decimal places which would be efficient and accurate. We could also heat a larger amount of water for the same reason. The entire apparatus could be put into a sealed environment such as a large jar with vent holes at the bottom and a small hole the top for stirring the water. The oxygen needed for the reaction would be sucked into the jar through the holes at the bottom and so the heat produce would be trapped in the environment and could be measured.
A more detailed trend with the results could be obtained by continuing the experiment with alcohols that had larger molecules, i. e. more carbon atoms. Also the experiment would be repeated more than twice to allow us to identify and eliminate the results even further. The evidence is reliable in showing the sort of trend that would be produced. The anomalous results were also very small and still show the trend clearly and so the results are accurate. The difference in the actual result and the predicted results can also be fully accounted for.
The actual results are also more realistic in terms of energy transfer as it takes into account the energy loss. The obtained evidence is sufficient to support a firm conclusion that as the molecular size of the alcohol increases so does the amount of energy released. This is because the results show this trend very clearly and are similar to the predicted results. The anomalies are also not far from the line of best fit and so support the trend making them reliable.
Even though the actual results differ from those that were predicted, it can be explained by the fact that energy is lost to the environment. Further work for this investigation would include testing to see the rate at which energy is produced; how long it takes for each alcohol to heat the water by a certain amount. My prediction would be that the alcohols with the larger molecules would take less time because they have more bonds and so more energy is released in a certain amount of time, and so it would heat the water faster.
Additional evidence for the conclusion could also be obtained by continuing the experiment with more alcohols with more carbons and so allowing us to gain a more detailed trend in the relationship. Also by replacing the calorimeter with a thermocouple would allow us to see a more accurate trend and find other factors apart from heat loss that may cause anomalous results. Steven John 11c Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.