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Determining and comparing the heats of combustions of alcohols

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Introduction

Anupma Raj-12i May 7, 2007 WHICH ALCOHOL IS THE BEST FEUL BETWEEN METHANOL, ETHANOL AND PROPANOL? INTRODUCTION: In this experiment I will determine the amount of heat energy involved in a chemical change. When an alcohol burns it produces carbon dioxide and water as products. Energy is also released in the reaction. I will be determining the amount of heat liberated when three alcohols burn, and compare their energy output, i.e. their heat of combustion. We will be using methanol CH3OH , ethanol C2H5OH , and propan-1-ol CH3CHOHCH3/C 3H 7OH. RESEARCH QUESTION: To investigate which alcohol gives out most energy per gram/mol/cm3 and hence, is the best fuel. HYPOTHESIS: I think that propan-1-ol will give out the most energy during combustion followed by ethanol and then methanol and hence, propan-1-ol will be the best fuel. During complete combustion of an alcohol, the energy is produced from formation of combustion products CO2 and H2O. Thus, Heat of Combustion should increase approximately linearly with the number of Alcohol Carbon atoms and as the formula suggests, propan-1-ol has more carbon atoms than methanol and ethanol. ...read more.

Middle

Change in temperature = (16.4+15.9)/2 = 16.15�C or 16.15K Mass of water used = 100ml = 0.1kg Specific Heat Capacity of Water: 4200J/KgK Therefore, energy change = 16.15 x 0.1 x 4200 = 6783J. Mass of methanol alcohol used is (1.099+1.107)/2 = 1.103g Therefore, the amount of energy given out for 1.103g is 6783J. Number of moles propan-1-ol used = (mass/molar mass) = 1.103/32.05 =0.0344 moles Therefore, 0.03440 moles --> 6783J 1 moles --> (6783/0.0344) = 197180.23J = 197.2kJ Energy change of Copper Calorimeter = mass x specific heat capacity x change in temperature. Change in temperature = change in temperature of water (ASSUMING) = 16.15K Mass of copper calorimeter = 186 g = 0.186kg Specific Heat Capacity of Copper: 390J/KgK Therefore, energy change = 16.15 x 0.186 x 390 = 1171.52J = 1.17kJ Total energy change = 197.2kJ + 1.17kJ = 198.4kJ Therefore, the total energy change for methanol is -198.4kJ. The value is negative because the energy is given out (as we can feel the energy being radiated when we are heating the water and hence, we know the reaction is exothermic). ...read more.

Conclusion

While measuring the heat transfer from the flame to the copper calorimeter, a lot of heat was lost to the environment. The experiment was designed such that this was an inevitable error. 2. We were measuring the volume of water in the measuring cylinder as a lot of bubbles formed which prevented the accurate measurement of the volume. 3. We kept the room ventilated as the flow of air cooled down the copper calorimeter and hence, we did not get a precise reading for the temperatures. 4. We assumed that there would be complete conversion to heat energy when the alcohols were burnt. 5. We assumed that the change in temperature of water equaled the change in temperature of the alcohol. IMPROVEMENTS: Here are a few improvements we could make: 1. To prevent the formation of bubbles while measuring the volume of water, we could pour the water from the tap into the measuring cylinder very slowly so as to reduce the chances of the formation of bubbles. 2. We could place some sort of blockage such as a glass shield around the flame/experiment to prevent the air flow in the room from affecting the results of the experiment. 3. We could take more trials so as to reduce the systematic errors and obtain more precise and accurate results. ...read more.

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