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# To determine which alcohol, out of ethanol and propanol, is the better fuel. By calculating the enthalpy change of combustion for ethanol and propanol I will find how much energy is released per mole of each alcohol.

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Introduction

WHICH IS THE BEST FUEL - ETHANOL OR PROPANOL? OBJECTIVE: To determine which alcohol, out of ethanol and propanol, is the better fuel. By calculating the enthalpy change of combustion for ethanol and propanol I will find how much energy is released per mole of each alcohol. To do this I will completely combust the alcohols in air, so I can then calculate how much energy is released per gram of alcohol and compare these results. BACKGROUND When establishing which alcohol is best to use as a fuel we must first consider the qualities that a good fuel must have. Some examples of these qualities are: The amount of energy released. The speed at which a fuel releases its energy - which needs to fairly high. Its' octane rating - The higher the octane number the more the fuel exhibits greater resistance to preignition. This is based on a scale from 0 (heptane) to 100 (iso-octane). Energy value - this is an expression of the potential energy in the fuel. Easy ignition - but not too flammable. The quality of fuel that I am going to measure is the amount of energy that it releases. Generally the octane number decreases as the number of carbon atoms increase. Also the greater the potential energy transfer the greater the amount of energy that can be lost. This fact must be kept in mind when deciding on which fuel is best. Enthalpy change of combustion (?Hc?) is the enthalpy change when one mole of an element or compound reacts completely with oxygen. ...read more.

Middle

Also it reduces any human errors on reading the temperature. The electronic balance gives an accurate mass figure to 2 d.p. I used the fact that 1 ml of H2O weighs 1g, so while measuring out the different masses of water I can keep results accurate. Propanol can show structural isomerism so by using propan-1-ol the alcohol group is on the end carbon making it a straight chain alcohol, like ethanol (ethanol cannot show isomerism). I do not know whether the position of the alcohol group or branching within the molecule effects the enthalpy change. I need to use alcohols with as similar structures as possible, with the only difference being the number of carbon atoms within the molecule. The masses of water I decided to use for the experiment were 50g and 100g. I conducted two tests with mass 50g and two with 100g for each alcohol, thus obtaining four results for each. I used two different masses to determine whether the accuracy of my experiment increases with a greater or smaller amount of water. On a trial run of the experiment it was found that too much heat was lost to the surroundings. For this experiment I can reduce the heat loss by putting a lid on the calorimeter with a small hole for the probe, by putting the calorimeter as close to the wick as possible, and by enclosing the set apparatus with aluminium foil, which would reflect the heat back. However space would be needed for the air to get in. ...read more.

Conclusion

The fact that the range for the enthalpy changes of propanol is so large could be because of the different amount of heat lost. The highest result for ?Hc? of propanol was 654.71 kJmol-1, the fact that this was so high compared to the other results may be because it was done on a separate day. My experiment was fairly accurate however inaccuracies could have occurred from the lid of the calorimeter. The first day a plastic lid was used and some of it melted. The second day foil was used instead. This would change how much heat was lost. Inaccuracies could also have occurred by how well insulated the experiment was. The method that was more accurate was by using Hess's Law. Even though this proved to be more accurate it is a specific value and for each experiment that is done conditions change and so would the results One way of improving my results without redoing another experiment would be by measuring the energy transferred to the calorimeter. The energy form the fuel is used to heat up the copper calorimeter, which then transfers the heat to the water. Not all the heat goes to water. The specific heat capacity of copper is 0.385 Jg-1K-1, this value can be used to measure the energy transfer with the known mass of the calorimeter. Unfortunately this was not measured and therefore can not be calculated, but it is worth considering. A way of improving the experiment would be to use a method that does not use specific heat capacities. There are two ways to do this. One way would be to use a flame calorimeter and the other a bomb calorimeter. ...read more.

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