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Experiment to Measure the Heat of Combustion of Butanol.

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Introduction

Experiment to Measure the Heat of Combustion of Butanol Aim: To find out the heat of combustion of a specific alcohol (in this case, Butanol). Combustion is the energy released when 1 mole of a fuel burns in pure oxygen. Background Knowledge: An exothermic reaction gives out heat, because chemical energy is converted into heat energy. It is opposite to an endothermic reaction - one that takes in heat. When we burn a fuel, in this case Butanol, it is called combustion. Combustion usually takes place in the air when the fuel combines with oxygen. However, substances can be burned in other gases. Combustion does not usually happen spontaneously but is triggered by heat. Variables: There will be two independent variables, and these will be, that the temperature will be allowed to rise roughly 30�C, and that the type of alcohol used in each case will differ. There will also be a dependant variable - the mass of the alcohol which will be burnt is unknown before the experiment takes place. ...read more.

Middle

The lamp will then be weighed again, and the final mass recorded. The difference in mass can then be calculated. The temperature increase will also be recorded. Results: Original Water Temperature = 21�c Final Water Temperature = 51 �c Rise in Water Temperature = 30 �c Original Mass of Lamp = 229.8g Final Mass of Lamp = 224.52 Decrease in Mass of Lamp (Mass of Butanol Burned) = 5.28g Assumptions - density of H2O = 1g/cm�, so 100cm� = 100g - specific heat capacity of H2O = 4.2g���c�� 100cm� x 4.2J���c�� x 30�c = 12,600J Mass of butanol burned = 5.28g To find 1 mole of butanol: Mr (C4H9OH) (C=12, H=1, O=16) = (12x4) + (1x9) + 16 + 1 = 48 + 9 + 16 + 1 = 74 Moles = mass/molar mass = 5.28/74 = 0.0714 0.0714 moles = 12,600J 1 mole C4H9OH = 176,471 Class Results Table: Alcohol Equation Molar Mass Energy 1st result (J) ...read more.

Conclusion

Two groups collected results for all but one of the alcohols, and the results could be affected by the efficiency of the spirit lamps. There was no way of testing the efficiency beforehand, without conducting a whole new experiment. Anomalous Results - There was one anomalous result, and this was the result recorded for Propanol. There is no exact reason as to why this happened, but as is visible on the graph, the result is below the rest. Perhaps the spirit lamp was faulty or inefficient, or the results were not read accurately. This result affects the conclusion, and as Propanol cannot be counted, Methanol appears to be the least efficient fuel. Further Work - To make the conclusion more firmly based, an experiment could be conducted beforehand to test the efficiency of the spirit lamps themselves. This would perhaps make the results of this experiment more accurate. Also, an experiment could be carried out after this one, to find out the same thing, but using different variables, such as using different alcohols, or different methods of burning the alcohols. ...read more.

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