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Investigation into the energy released by burning alcohols

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Introduction

Investigation into the energy released by burning alcohols Aim The aim of my experiment is to investigate how much energy is released by 5 different alcohols when they are burnt. These are Methanol, Ethanol, Propanol, Butanol and Pentanol. Scientific Theory In the following experiment I will be investigating how much energy is given off when you burn an alcohol. The 5 alcohols I will be investigating are methanol, ethanol, propanol, butanol and pentanol. All of these are part of the homologous series and so they all contain the functional group O-H. Their structures can be shown as follows: Therefore the general formula for alcohols is: When each of these fuels is burnt they are all exothermic, combustion reactions. A balanced combustion equation for methanol would be CH3OH + 11/2 O2 ? CO2 + 2H2O. A combustion reaction is when the fuel burns in the oxygen in the air producing carbon dioxide and water. The combustion equation can be used to work out the energy given off by using bond calculations. The reactions are exothermic because they give off energy to the surroundings and so the energy released that I work out will be a negative number. ...read more.

Middle

book and have found the same thing: Methanol: -726.0kJ/mol Ethanol: -1367.3kJ/mol Propanol: -2021.0kJ/mol Butanol: -2675.6kJ/mol Pentanol: -3328.7kJ/mol Finally, I can do bond calculations to see a specific pattern. The energies for each bond used are shown below in kJ/mol: C-H: 413 C-C: 347 C=O: 805 C-O:358 O=O:498 O-H: 464 I then did the calculations for each alcohol using these bond energies. An example is for Methanol: CH3OH +11/2O2 ? CO2 + 2H2O 2061 + 747 1610 + 1856 2028 - 3466 = Preliminary Work In my preliminary work I burnt butanol to see what sort of number I would get and to ensure the equation would work. The final answer was -695.8KJ/mol. I now know that I will find my results are around this number and that most of them will be smaller than this. Initially I was planning to burn each fuel for a length of 2 minutes and look at the temperature change but I will not do this because the concept of time in the equation is irrelevant. Instead, I will now keep the temperature change constant and ignore the time. In my preliminary experiment I found out a lot of things, which I need to do make my experiment better. ...read more.

Conclusion

Variables There are many things that I will have to do to ensure that my experiment is a fair test. I will only change one factor and that will be the fuel that is been burnt. * For each test the temperature change will be 30 C. This means the water will rise from a temperature of 20 C to 50 C in each test. * I will repeat each test three times so I can obtain three sets of results for each alcohol and then take an average. This also makes it possible to see any anomalies * The calorimeter will always be 2cm above the top of the wick of the burner for each test so that the same amount of heat is transferred in each test. * In each test I will fill the calorimeter with 50cm3 of water. * The thermometer in each test will be suspended in the calorimeter using a clamp on the clamp stand. * After each test I will clean down the bottom of the calorimeter of any soot that has built up as this could affect the conductivity of the calorimeter in the next test. * * * * ?? ?? ?? ?? Claudia Spink 10MJ ...read more.

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