Fuels Coursework Plan
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Comparing the Enthalpy change of combustion of different alcohols Saidul Amin 12LT Combustion reactions are exothermic. The chemical reactants loose energy and the products end up with less energy than the reactants had. Enthalpy change is the measurement of energy transferred to and from the surroundings. Enthalpy change is worked out as: ?H= H products - H reactants The diagram below shows an enthalpy level diagram for an exothermic reaction. I will expect all my enthalpy change values to be negative as combustion is an exothermic reaction, and therefore energy is being lost to the surroundings. It is however obvious that these values will change for different alcohols, as their molecular structures are different. There are three independent variables which can be investigated in this experiment and these are chain length of the alcohol, amount of branches there are in the alcohols and also the position of the functional group on the alcohol. In this experiment I will be seeing how the chain length of different alcohols affects change in enthalpy. In turn this means that I am testing how an increased number of carbon atoms on the alcohol effects change in enthalpy. Therefore I will be using alcohols with different number of carbon atoms, and these will be Methanol, then Ethanol, Propan-1-ol and Butan-1-ol. I will then combust these alcohols and see what values they give for enthalpy changes, and then I will go on to comparing them.
Methanol CH3OH Ethanol C2H5OH Propan-1-ol C3H7OH Butan-1-ol C4H9OH For the extension experiment I will be using Propan-1-ol, Propan-2-ol, Butan-1-ol and Butan-2-ol. Propan-2-ol C2H8O- Safety glasses must be worn. Same measures of first aid as ethanol. Butan-2-ol C4H10O- To use this fuel safety glasses must also be worn and it must be used in a well ventilated area. Same measures of first aid as methanol. Equipment Copper Calorimeter Heatproof mat Accurate balance (2.d.p) Funnel - to avoid spillages which may be dangerous when close to lit fuel burners Thermometer (0.1 ºC divisions) Heat shield Clamp stand Measuring Cylinder Glass rod Alcohol (fuels in burners, at least 200g of each) -Methanol -Ethanol -Propan-1-ol -Butan-1-ol Bunsen burner Splint Lab coat Distilled Water Goggles Diagram Precision and Accuracy I will work carefully as I do these investigations, not only for health and safety issues, but also for accuracy and precision. I will use all apparatus correctly as far as my understanding of them allows me to, which will make my measurements as precise as possible. This means that my repeats should almost be the same as my results, and if not they should be very close. They should also be to such an extent of accuracy that anyone else using the same procedure was to do it then results should virtually be identical. Therefore this will indicate the reliability of my measurements.
0.52 1075.85 Rpt 2 100.00 21.00 39.00 18.00 184.38 183.88 0.50 1118.88 Average KJ mol-1 1104.54 Butan-2-ol 100.00 21.00 39.00 18.00 153.57 153.03 0.54 1036.00 Rpt 1 100.00 21.00 39.00 18.00 153.03 152.53 0.50 1118.88 Rpt 2 100.00 21.00 39.00 18.00 152.53 152.00 0.53 1055.55 Average KJ mol-1 1070.14 Theoretical calculations of Enthalpy Change By using the bond enthalpy values (from the data tables), the enthalpy change of combustion can be calculated theoretically. For example Methanol + Oxygen Carbon dioxide + Water CH2OH (g) + 1.5 O2 CO2 + 2H2O C-H 413 kJmol-1 C-O 336 kJmol-1 2 x C=O 2 x O-H O-H 464 kJmol-1 O=O 498.3 kJmol -1 C=O 805 kJmol-1 3x C-H 1x C-O + 1.5 x O=O 1x O-H 2039 kJ + 747.45 kJ 1610 kJ + 1856 kJ 2786.45 - 3466.00 Enthalpy change of combustion of methanol = -679.55 kJmol-1 It is apparent that my result differs to that of the data sheets, which shows that the Enthalpy change of combustion of methanol is -726 kJmol-1. This is because the value given in the data sheets is the enthalpy change of combustion of methanol in standard conditions, but also the fact that the exact bond enthalpies depend on the different compounds used to obtain the bond enthalpy. After having worked out all the calculations, I can then produce my final results for my experiment like this: Fuel Enthalpy change of combustion (kJ mol-1) Methanol Ethanol Rest of fuels...
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