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Combustion of Alcohol's.

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Combustion of Alcohol's When alkanes burn, an exothermic reaction takes place; energy is released as heat. Energy is needed to break the bonds on the left-hand side of each equation. However, once they have been broken down, they are then reformed and this process gives out energy as heat. The aim of our experiment is to find out which alcohol, when burnt, gives out the most energy. We are going to do this by burning different alcohols below a test tube of water. We will wait until the water has risen from 25�C to 80�C and will calculate the mass of alcohol that has been needed to create this temperature change. We will weigh each alcohol before and after each experiment. In my preliminary work, I was able to work out the average amount of energy given out by each alcohol when burnt. Using the bond energies of each type of bond, I was able to work out the energy needed to break the left-hand side of the equation, and the energy created when forming the bonds on the right side of the equation. ...read more.


I will make this out of aluminium foil because the shiny side will reflect the heat well. I weighed each alcohol before igniting it, and recorded the weight. I then placed the alcohol under the skirt and only removed the lid just before it was lit, to reduce the amount escaping into the atmosphere. I carefully watched the thermometer until it had risen to 80�C. As soon as it had reached 80�C, I put out the flame. I then weighed the alcohol again and noted that down. I was then able to work out how much alcohol was used. I did each alcohol three times so that I could make my results as accurate as possible. The results I obtained are below. Water = 20ml Temperature of Water = 25 C - 80 C Weight/Mass(g) (BEFORE) Weight/Mass(g) (AFTER) Mass(g) Change Methanol 275.0 273.6 1.4 Ethanol 225.4 224.4 1.0 Propanol 260.4 259.3 1.1 Butanol 244.3 242.5 1.8 Pentanol 218.4 217.4 1.0 Weight/Mass(g) (BEFORE) Weight/Mass(g) (AFTER) Methanol 226.4 224.8 1.6 Ethanol 243.5 242.3 1.2 Propanol 229.2 228.0 1.2 Butanol 234.5 233.4 1.1 Pentanol 228.9 228.3 0.6 Weight/Mass(g) ...read more.


Then I must divide my result by this: 0.7/88 = 0.007954 My results are shown on the next page. This graph shows that my prediction was correct. Pentanol used the least amount of moles to heat the water, and methanol used the most. I can therefore conclude that the longer the hydrocarbon molecule, the more energy is released when making bonds. I think my experiments went pretty good. There were a few discrepancies that could have occurred for many reasons. Poor quality equipment or simply human error could have caused this. I think there is one main anomaly that I can identify. This is on the 3rd attempt of the experiment, using methanol. Somehow, after burning the alcohol, it gained 0.7g of mass??!! Apart from this, I think the rest of the experiment went okay. The results came out pretty good. I think the quality of my results is poor. However, I think that they could be improved by repeating the experiments with more time and less haste. Also, I think it would be beneficial to use more alcohols, such as hexanol, heptanol and octanol. This would give me a wider range of results and I would be able to draw a better conclusion that was more precise. Amy Baker ...read more.

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