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The Heat of Combustion of alcohol.

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The Heat of Combustion of alcohol Hypothesis When alcohol is burned, the energy that is released can be transferred to the water in a calorimeter. The temperature rise can be used to calculate the amount of energy transferred. The structures of different alcohols are different from each other. They are a family of organic compounds. Alcohols are very flammable substances and burn well in the presence of oxygen, forming carbon dioxide and water vapour, and giving out plenty of energy. Example Ethanol C2H5OH (l) + 3O2 (g) 2CO2 (g) + 3H2O (g) + heat The different compounds follow a general pattern for the structure of CnH2n+2. The larger structure means the longer the chain and thus a higher the boiling point. This means that more heat is needed in order to break their bonds for those further down the chain of reactions. Aim Investigate which alcohol gives off the most energy when burnt in a spirit lamp. Prediction I predict that the alcohol that will give the most energy when burnt will be pentanol. Out of the five alchols which we will be testing (i.e. ...read more.


Propanol C3H7OH + 5O2 3CO2 + 4H2O 2 C-C 346 x 2 = 692 7 C-H 412 x 7 = 2884 1 C-O 358 x 1 = 358 1 O-H 464 x 1 = 464 5 O=O 498 x 5 = 2490 = +6888 Energy Given Out 6 C=O 743 x 6 = 4458 8 O-H 464 x 8 = 3712 = -8170 6888 + -8170 = -1282 kj/mol Energy needed to break bonds Butanol C4H9OH + 6O2 4CO2 + 5H2O 3 C-C 346 x 3 = 1038 9 C-H 412 x 9 = 3708 1 C-O 358 x 1 = 358 1 O-H 464 x 1 = 464 6 O=O 498 x 6 = 2988 = +8556 Energy Given Out 8 C=O 743 x 8 = 5944 10 O-H 464 x 10 = 4640 = -10584 8556 + -10584 = -2028 kj/mol Energy needed to break bonds Pentanol C5H11OH + O2 3CO2 + 4H2O 4 C-C 346 x 4 = 1384 11 C-H 412 x 11 = 4532 1 C-O 358 x 1 = 358 1 O-H 464 x 1 = 464 5 O=O 498 x 5 = 2490 = +6888 Energy Given Out 6 C=O 743 x 6 = 4458 8 O-H 464 x ...read more.


They are similar to the theoretical results. Supporting Prediction The results were true my prediction. They followed the same pattern as I had mentioned and the reasons for this seems from the results were also true for the same reasons. Conclusion The structure of the alcohol seems to be important in the time it takes for water to heat up. Not only does it mean the alcohol itself have more structure to burn but as a result what is given off when burnt also has more molecules and structure. Evaluation The test was satisfactory. The results had come out as planned and the theory was correct. The factors which would effect the test were taken into account as much as possible. One variable which was not dealt with was the fact that the heat was lost into the atmosphere. This could have been dealt with using draught screens but this could not be done due to insufficient supplies. Also accuracy was lost in that we were not able to repeat the test again due to time and practicality. I felt that everything else was accurate especially measuring the weight as we had an electronic scale to measure it for us. Overall the test was carried out sufficiently and the results were clear and of a high standard. ...read more.

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