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Enthalpy Experiment

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Introduction

Lauren Crawley 10 LE 6-March-2002 Enthalpy Experiment I will be trying to obtain reliable results which tell me the relationship between the number of carbon atoms, in particular alcohols: Methanol, Ethanol, Propan-1-ol and Butan-1-ol, and the amount of heat energy given out, known as the enthalpy of combustion. The combustion process is the making and breaking of bonds. In my experiment heat will be given out (it will be an exothermic reaction) In an exothermic reaction the products are at a lower energy level than the reactants, the difference is the heat energy. The complete combustion of an alcohol is when it reacts with oxygen in the air to form water and CO2. Fuel is a substance that is generally burned to produce thermal energy. Using these 4 alcohol fuels I aim to find out how much heat energy each alcohol produces. I am going to investigate this energy release by burning alcohol- "enthalpy of combustion" and how the number of carbon atoms in each of the alcohols affects the enthalpy change occuring during combustion. Once my results have been obtained I will compare them against the theoretical enthalpy values. ...read more.

Middle

All of these calculations needed to be performed to obtain my final results. No. of Moles = Mass Burnt / RMM * Methanol: Mass used- 0.81g / 32 = 0.025 moles * Ethanol: Mass used- 0.56g / 46 = 0.012 moles * Propan-1-ol: Mass used- 0.5g / 60 =0.0083 moles * Butan-1-ol: Mass used- 0.47g / 72 =0.0064 moles Now i can work out the enthalpy by using the results from the previous two calculations. Enthalpy = Energy Transferred to Water (J) / Moles of Fuel Burnt (mol) * Methanol: 5178.6 / 0.025 = 207.144 kJmol-1 * Ethanol: 4968 / 0.012 =414.05 kJmol-1 * Propan-1-ol: 5103 / 0.0083 =614.82 kJmol-1 * Butan-1-ol: 5040 / 0.0064 =787.5 kJmol-1 Now each of these values can be plotted on a graph, against the number of carbon atoms. Below is the table of these results. My Final Results Table ALCOHOL ENERGY TRANSFERRED NUMBER OF MOLES ENTHALPY CHANGE TO WATER Methanol 5178.6 J 0.025 -207.144 kJ/mol-1 Ethanol 4868.6 J 0.012 -414.05 kJ/mol-1 Propan-1-ol 5103 J 0.0083 -615.83 kJ/mol-1 Butan-1-ol 5040 J 0.0066 -763.63 kJ/mol-1 Analysis My prediction states that the amount of heat produced per gram of alcohol will increase as the number of carbon atoms per molecule increases. ...read more.

Conclusion

Other factors affecting the accuracy of my results could be that, sound and light energy will have been lost in the room. The beaker itself will have absorbed some of the energy. The alcohol containers had different amounts of alcohol and varying wick sizes, these factors contributed to the varying size of the flame; which sometimes never even touched the beaker. Also the environment in which my experiment was conducted could have contributed to my low enthalpy values. A lack of oxygen could have caused incomplete combustion, this is, however, unlikely. The room temperature may have acted as a cooling agent. I conclude that the classroom was a difficult environment in which to perform this experiment, there are so many potential ways of losing energy, as everything likes to gain heat energy. Apart from sufficient heat insulation and, no gusts of air to take heat away from the experiment there are no ways to obtain results close to the theoretical enthalpy values. From my graph i notice the obvious anomolous result is in the combustion of Butan-1-ol, however it wasn't abnormally anomolous and I think it will be due to natural error, I could repeat that part of the experiment again, to gain an average an re-plot it on the graph. ...read more.

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