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Enthalpy Change - Alcohols

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Introduction

In this experiment, I will be investigating the levels of energy found in alcohols. Fuels like petrol and diesel come from non-renewable fossil fuels, that power machines like cars. However, these are running out fast, and an alternative fuel must be found as soon as possible. Alcohols could be used as fuels and also it's from a renewable source, as they can be grown and fermented. For this experiment I will need to calculate Enthalpy change (?H). Change Enthalpy Mass of Water Change Temperature Specific heat Capacity (4.2 j/g) Firstly, I will need a calorimeter - A calorimeter is a device used for measuring the heat of chemical reactions or physical changes as well as heat capacity. To find the enthalpy change per mole of a substance I will need to burn the alcohol underneath the calorimeter and during this process temperatures are noted. To hold the burner closer to the calorimeter I will use wooden blocks to support it. Attached to the top of this calorimeter will be a water pump, to suck up as much as possible of the hot air. The alcohol burners I will use will be 3x Ethanol, 3x Methanol, 3x Propanol & 3x Butanol, I will do the experiment three times for each to get a 'fair' result. ...read more.

Middle

22.55�c. After my preliminary testing, I found that the burner could easily be affected by heat loss via the calorimeter; if the gap between the burner and the calorimeter is too much then too much heat will be lost. If it's too close, the burner will not produce the full potential of heat. This is why I am using wooden blocks to firmly hold it in the correct place. Another way of preventing heat loss is a simple water pump, this quite simply attaches to the top if the calorimeter and sucks up the hot air through the calorimeter. Finally, the calorimeter could produce hotspots in the water, so a stirrer will be necessary. I am not expecting perfect results every time, but if an anomalous result occurs I will still include it but show the anomaly either in my results tables or on my graph. Time (seconds) Temp (�c) Alcohol 0 30 60 90 120 150 180 Weight Before (g) Weight after (g) Ethanol 22.5 25.6 25.8 26.3 27.4 28.5 29.5 31.49 30.94 Methanol 21.4 21.5 21.9 22.4 23 23.7 24.6 29.37 28.80 Propanol 21.2 21.5 21.9 22.3 22.8 23.4 23.9 32.62 32.34 Butanol 20.5 22 21.1 21.5 21.8 22.2 22.5 30.41 30.13 Time (seconds) ...read more.

Conclusion

The relative mass: Methanol is 32 Ethanol is 46 Butanol is 60 Propanol is 74 Following this, I need to divide the energy by mol; this will give me my result in J mol-1, the final stage will be to divide this number by 1,000 to get my final result in KJ mol-1. The correlation between the Mr and energy of combustion is as one gets higher, so does the other. Although you need more energy per Mr to break the bonds, the higher the Mr the higher the energy you get back out of it. I believe that my evidence is fairly reliable, but obviously not perfect. My results to follow a trend but enthalpies of combustion are not even half way close. Techniques should be improved to receive better results, for example; the way we equilibrate the calorimeter and check the temperature. The calorimeter should be properly equilibrated before we even touch it, but also every time we touch the calorimeter the temperature of the water could be affected, it may only be 1� or so but the results will be effected. Also the temperature needs to be checked throughout the calorimeter as hotspots are produced. The results - energy of combustion - we received compared to the actual results are quite different, e.g. Methanol; my result is 221.21 KJ mol-1 whereas the actual results are 726 KJ mol-1. ?? ?? ?? ?? Chemistry Coursework Page ...read more.

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