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Comparing the enthalpy changes of combustion of different alcohols.

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Introduction

COMPARING THE ENTHALPY CHANGES OF COMBUSTION OF DIFFERENT ALCOHOLS Analysis Results Table Alcohol Initial Temperature (c) Final Temperature (c) Initial Mass (g) Final Mass (g) Methanol 20 35 188.36 186.40 Ethanol 20 35 233.92 232.31 Propan-1-ol 20 35 244.67 243.24 Butan-1-ol 20 35 213.54 212.29 Pentan-1-ol 20 35 195.44 194.46 Hexonal 20 35 217.38 216.66 Alcohol Mass Loss (g) Relative Formula Mass Number of Carbon Atoms Methanol 1.96 32 1 Ethanol 1.61 46 2 Propan-1-ol 1.43 60 3 Butan-1-ol 1.25 74 4 Pentan-1-ol 0.98 88 5 Hexonal 0.72 102 6 Calculations The first step I need to take in calculating the amount of heat absorbed by the water in each experiment is to find out how much energy is transferred to the water to raise its temperature. ...read more.

Middle

= / 1000 for kJ = 205.71 kJ mol-1 (2.d.p) Table for all enthalpy changes Alcohol Moles Enthalpy Change (kJ mol-1) Methanol 0.06125 205.71 Ethanol 0.03500 360.00 Propan-1-ol 0.02383 528.75 Butan-1-ol 0.01689 746.00 Pentan-1-ol 0.01113 1132.08 Hexonal 0.00758 1662.27 Conclusion As my graph shows, as the number of carbon atoms in the alcohol molecules increase, so does the enthalpy change of combustion. This is because the more carbon atoms, and therefore hydrogen bonds, that the molecule possesses, the more energy is needed to break the larger amount of bonds. Evalutation I am pleased with my experiment as it returned results to confirm my prediction. I did not observe any anomalies which suggests that the results were accurate in relation to each other (suggesting that there were no human errors) ...read more.

Conclusion

9. The size of the wick. 10. Not all of the water was the same temperature. 11. The flame size changed due to the type of alcohol, hence it was a different distance away from the beaker each time. I could obtain a better picture of how the number of carbon atoms affects the heat of combustion in two ways. 1. I could extend my current experiment by testing other alcohols such as heptanol or octanol as well as by doing more repeats to increase the accuracy of my results. 2. I could conduct a similar experiment with other homologous series of hydrocarbons such as the alkanes or the alkenes. This would allow me to compare the results from each experiment and compare how the number of carbon atoms in the chain affects the heat of combustion. ...read more.

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