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Plan and carry out an investigation to determine which of the four alcohols is the most exothermic.

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Introduction

Comparing Heat Outputs Of Alcohols By Joanna Lally 11B1 Brief Plan and carry out an investigation to determine which of the four alcohols is the most exothermic. Prediction I predict that the most heat given out per mole burned would be by Propanol because the size of the alcohol molecules might increase with heat. Alcohols produce heat when they burn in oxygen or air. The amount of heat produced per mole of alcohol will be proportional to the amount of air present. Full combustion should generate two products only: carbon dioxide and water vapour. Hypothesis Within a molecule there are bond energies that are holding the atoms together. When the fuel combusts a chemical reaction takes place, this breaks the bonds, this requires energy, and makes new bonds this gives out energy. The energy differences between the two tell us how much energy was given out or taken in. We can show this on a graph. Alcohol particles will break their bonds when they mix with oxygen. This is known as exothermic reaction. Boiling points will be increased because energy is needed bonds can be formed and broken. Breaking bonds need less energy than is needed to form bonds - exothermic reaction. ...read more.

Middle

When the temperature has risen to 30�C, I quickly place the top back on the spirit burner. Now I re-weigh the alcohol. o find out how much alcohol has been burned I subtract the finishing mass from the starting mass. Fair Test I will try my best to keep this experiment fair. All the variables must be controlled. These are as follows - The scale reading has to be on zero before weighing the spirit burner and alcohol. The alcohol must be weighed accurately. During weighing the spirit lamp must be covered to avoid and evaporation of the alcohol. The alcohol has to be weighed accurately before and after the experiment. The alcohol has to be blown out immediately when the water temperature has been raised 30 degrees; it must be covered after the experiment to avoid evaporation. Any remaining carbon is to be cleaned off the beaker so that the flame can easily heat the water. Exactly 100ml of water is to be used. The length of wick on the spirit burner must be the same. The height of the burner from the beaker (the brick height) must be the same. The beaker must stay the same shape as well because if it is not the flame may have more surface area of where to heat the water. ...read more.

Conclusion

Also, Methanol had the lowest amount of heat produced, just as I had predicted. So, I conclude that the most efficient alcohol out of the ones that I had investigated was Propanol, and the least efficient was Methanol. As far as I can see, there are no patterns or trends in my results Evaluation Looking at the overall experiment and procedure used to find the results obtained, I thought that it was a good enough way to investigate the combustion of different alcohols. The results I got were near enough of what I would have expected from the alcohols used, which I mentioned in my conclusion. The only set of results I was unhappy with was Methanol, with quite a big percentage error compared to the rest. The procedure of the experiment was good enough of finding out the energy gained from the individual alcohols, but changes could have been made to make the reliability of the results more accurate. I could have measured the amount lost after recording the alcohol temperature after about 10 minutes. These results will be really high but we'll have a greater difference between each alcohol. I do think that the results which I have obtained are reliable enough for this experiment. There were no anomalous results. Joanna Lally 11B1 Chemistry GCSE Coursework - 1 - ...read more.

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