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To investigate the amount of heat released in the burning of fuels: ethanol (C2H5OH), propanol (C3H7OH) and butanol (C4H9OH).

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Introduction

Plan ------------------------------------------------AIM---------------------------------------------- To investigate the amount of heat released in the burning of fuels: ethanol (C2H5OH), propanol (C3H7OH) and butanol (C4H9OH). -------------------------------------------BACKGROUND---------------------------------------- ALCOHOLS Ethanol, propanol and butanol are members of a homologous series of compounds known as alcohols. They have a general formula, CnH2n+1OH. They all react similarly and have similar physical properties. MOLECULAR STRUCTURES Ethanol: (C4H9OH) H H H - C - C - O - H H H Propanol: (C3H7OH) H H H H - C - C - C - O - H H H H Butanol: (C4H9OH) H H H H H - C - C - C - C - O - H H H H H Energy is released when the bonds are formed between the new water and carbon dioxide molecules. The amount of energy produced by such exothermic reactions can be calculated by using the mass of the water x rise in temp x SHC (specific heat capacity). The specific heat capacity is the number of joules required to heat one gram of water by 1�C. Water has been chosen because it is safe, readily available, and has a reliable specific heat capacity of 4.2Kj The reaction that is involved in burning alcohols is exothermic because heat is given out. ...read more.

Middle

Below are the 'ideal energy values' (J/mol). These were obtained using knowledge of the equation used to find the 'heat of the reaction' i.e. the difference in energy between the reactants and products. It is given the symbol ?H. By definition, Heat of reaction, ?H = Energy of products - Energy of reactants Using the balanced equations for each of the reactions I continued as follows: Ethanol C2H5OH + 3O2 ==> 2CO2 + 3H2O ==> 5(C-H) = 5 X 412 = 2060 (C-C) = 348 (C-O) = 360 (O-H) = 463 3(O=O) = 3 X 496= 1488 + 4719 4(C=O) = 4 X 734 = 2936 6(O-H) = 6 X 463 = 2778 + 5714 5714 4719- 995 <--This is the difference in energy (?H). Therefore, 995KJ/mol is the energy released. Propanol 2C3H7OH + 9O2 ==> 6CO2 + 8H2O So to work out the energy per mole I used: C3H7OH + 41/2O2 ==> 3CO2 + 4H2O ==> 7(C-H) = 7 X 412 = 2884 2(C-C) = 2 X 348 = 696 (C-O) = 360 (O-H) = 463 41/2(O=O)=41/2X496 =2232 + 6635 6(C=O) = 6 X 734 = 4404 8(O-H) ...read more.

Conclusion

Error could have also occurred where the temperature had to be observed. Instead of a thermometer a temperature probe connected to a computer could have been used, this way there would have been no error involved in reading the thermometer. In further investigations, one could examine the combustion of fuels methanol, pentanol and hexanol. Investigations into the rate of reaction and the response to varying the material of which the beaker, or calorimeter is made are other ideas. Overall it can be said that the chosen method was unsuccessful in transferring a sufficient amount of the energy from the wick, where it was released, to the water. Heat was lost into the atmosphere in a number of ways. This heat was not, or could not be measured or accounted for. The main problem that the method gave was that concerning the limited number of results (only three alcohols were tested). With only three results it is impossible to single out anomalies and a correct line of best fit cannot be drawn. It has been decided that al results obtained are 'anomalies' to an extent because they are so different to the ideal results because much of the energy was lost to the surroundings and incomplete combustion occurred. ...read more.

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