Chemistry - Reactivity Serires report
4 star(s)
Alcohol Combustion Experiment Evaluation
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Introduction
Alcohol Combustion Experiment Evaluation In comparing my results with those of published data, I found that my calculated heats of combustion were not accurate. However they did all follow the trend that published data showed, and in that respect my results were correct. The reasons behind why my results were inaccurate are mainly due to heat loss and incomplete combustion. However, if I were to conduct the investigation again, I feel that my results would be more accurate and closer to those of published data. This is because I now know why my results were inaccurate. One of the reasons behind why my results were inaccurate was due to heat loss. The fact that there was a sufficient heat loss meant that the temperature rise figure required to work out the energy of combustion was inaccurate. This inaccuracy affected the whole of the results, and would have been emphasised as I multiplied the number of kilojoules up to 1 mol. I could solve this problem by decreasing the distance between the burner and the water tin, as this would have reduced the heat loss, although by doing this some heat still would have been lost to the surrounding air. ...read more.
Middle
However, the stirring would have to take place in an enclosed beaker, as by stirring, you are increasing the rate of evaporation, which will eventually reduce the temperature of the water. Another cause of inaccurate results was the time taken to weigh the burner after combustion. Weighing must be done fast as the alcohol will evaporate as it cools done. This evaporation will gradually decrease the mass of the alcohol. Even if the decrease due to evaporation were minimal it would still have a massive effect on the final outcome. As explained above, there are many ways and reasons why my results were not as accurate as they could have been. Although they are not completely accurate, due to heat loss and incomplete combustion etc., I still feel that the evidence is sufficient to support the conclusion. This conclusion was that as the alcohols series declined, the heats of combustions increased. From my graphs and tables of results I can see that my findings support this. I think that my results were reliable. This is because they were all done under the same conditions. ...read more.
Conclusion
* There is a stirrer - this would enable that all of the water was being heated. * The water is enclosed - this would mean that minimal energy is lost to the surroundings. * There is a constant supply of oxygen - required for combustion If were to use the above equipment, I would expect the results to be closer to reality i.e. closer to those results in published data. This is because there is a better air supply, less of the energy is lost to the surroundings and the water is enclosed and stirred. Also, the above equipment would solve the problem of incomplete combustion so the results are more likely to be closer to published data. However, they would still not be exact as some heat will always be lost and complete combustion cannot always be ensured. There would also be the same weighing problems regarding the burners. If the burners are not weighed as soon as combustion is finished, the alcohols will continue to disappear through evaporation, which would gradually decrease. Even a slight decrease from the exact mass change would have a significant effect on my overall results. Owen Williams 11.3 Heat of Combustion Investigation Evaluation ...read more.
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