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Combustion of Alcohols Investigation

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Combustion of Alcohols Investigation Aim The aim of this investigation is to investigate which of a number of alcohols methanol, ethanol, propanol and pentanol is the most efficient fuel. Possible Factors To Be Investigated There are four main factors that could affect the heating done by a fuel. These four factors are: * Distance. The greater the distance of the heat source from the water, the more energy will be needed to heat the water. For example: It will require a lot less energy for the heat source to heat the water from 5cm than it would if the heat source was 10cm away. An increase in the amount of heat lost to the surroundings will mean the fuel will have to burn more and release more energy to achieve the same heating affect. * Temperature Rise. A lot more energy is required to raise the same amount of water by 100oC than to raise it by 10oC. This means that the fuel will have to burn longer to increase the temperature of the water by a larger amount. * Volume of Water. A larger volume of water will require a larger amount of heat to raise its temperature to a certain level. For example: More heat energy will be required to raise 200cm3 of water from 20oC to 50oC than it will to raise a lesser amount of water by the same margin. * Size of Alcohol. Different types of alcohol are available to us at school and this is a key factor in choosing this for our investigation. ...read more.


The reaction that takes place in each one is an exothermic reaction, which increases with the alcohol. This happens because more energy is produced when new bonds are formed than the energy required to break the existing bonds. Therefore there is excess energy. This energy is released, in the form of heat to the surroundings. As the alcohol gets larger the amount of excess energy becomes larger therefore more heat is released to the surroundings. This is clearly seen in the enthalpy reactions where the amount of surplus energy is shown to get larger, as the difference between 'a' and 'b' gets larger as the size of the alcohol does. I am therefore able to hypothesise that that as the alcohol gets larger the fuel will be more effective and release more energy per mole and per gram. If you double the number of carbons in the chain, then the energy released will approximately double. I think this is because, when the bond energy before the experiment doubles, the calculated energy released doubles, and when reacted, shorter carbon chains burn slower, because they have less hydrogens. When the carbon chain doubles, the number of carbons double, the hydrogens almost by a factor of two, and the oxygens by two, i.e., two Hydrogens, and three oxygens, are added, when one carbon is added. That is to say that the bond energy being broken is increasing by 1918J every time, so you are almost going to get this doubling effect. Results Fuel Initial Mass Final Mass Difference in Mass Average difference Propanol 133.00 132.30 0.69 0.78 Propanol 79.61 78.75 0.86 Pentanol 36.38 35.75 0.63 0.61 Pentanol 35.70 ...read more.


However it is taken as a constant so when 21KJ is used later on in the enthalpy equation to work out the amount of energy given out by each mole it may be slightly wrong and therefore give a slightly inaccurate answer. When comparing the predicted results and actual results the same degree of inaccuracy was had every time. The actual results are around half the value of the predicted every time. This indicated to me that an inaccuracy is occurring in every experiment at around the same extent. This can only be as heat lost to the surroundings may have created another error. Heat-proof mats were used to surround the flame and try to concentrate the heat energy produced by the flame to heat the water and not simply be lost to the surroundings. There may have been, however holes where the heatproof mats connected which allowed heat out. These holes may have been different sizes each time the experiment was performed so therefore allowing different amounts of heat out each time. The heatproof mats also let much heat through them. This will be the same amount of heat for each fuel so the order of the effectiveness of the fuel will be the same. This is the reason to why our results obtained are 20% of the results predicted as that is the amount around that is the amount I would expect to be lost as heat. An improvement that could be made to the experiment would be to use a kalometer. ...read more.

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