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How much Energy is Released from the Combustion of Various Alcohols

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Introduction

How much Energy is Released from the Combustion of Various Alcohols Aim To investigate how much heat energy is released when various alcohols (methanol, ethanol, propan-1-ol, butan-1-ol, and pentan-1-ol) combust. SCIENTIFIC BACKGROUND AND PREDICTION Scientific Background of Alcohols Methanol, ethanol, propan-1-ol and butan-1-ol are part of the alcohol homologous compound series, which is defined by their function group of -OH. Below is the structure of ethanol: The general formula for alcohols is CnH2nn+1OH. As I have proved earlier on in my prediction, larger alcohol chains have release more energy when combusted because they have more bonds, but this also means they have a higher boiling point: Alcohol Formula Boiling point (oC) Methanol CH3OH 65 Ethanol C2H5OH 78 Propan-1-ol C3H7OH 97 Butan-1-ol C4H9OH 117 Pentan-1-ol C5H11OH 137 Ethanol burns with the following equation: Ethanol + oxygen ==> carbon dioxide + water 2CH3OH + 3O2 ==> 2CO2 + 4H2O This means that the burning of an alcohol (in this case ethanol) releases only carbon dioxide and water, which are environmentally friendly products so alcohols as fuels are environmentally friendly. The production of alcohol is also easy. It can be fermented: Glucose ==> ethanol + carbon dioxide Which is environmentally friendly or through the hydration of ethene: C2H4(g) + H2O(g) C2H5OH(g) Prediction I believe that larger chains of alcohol (e.g. propan-1-ol) will combust to release more heat per a mol than a shorter chain of alcohol s(e.g. ethanol). Scientific basis I believe this because using bond energies we can find out the energy stored in 1 mol or reactant and see how much energy is lost (endothermic reaction) ...read more.

Middle

The container should be as close to the wick as possible. The can will be placed just above the tip of the flame. Starting temperature of water: This should be similar all the way through, because of factors leading to evaporation of water due to higher temperatures. This should not matter too much as room temperature should remain constant. This cannot be changed and is not very significant either. Draft shields: Can affect how much heat gets to the container. A draft shield will be used. Stirring: Stirring the water in the can makes the water heat up faster. Therefore stirring can affect the results obtained. The cans should be stirred at a constant rate throughout the heating. Safety Safety goggles were worn throughout the experiment. Care was taken not to ingest the alcohol. Diagram Method The apparatus was set up as above. The starting temperature of the 250ml of water was noted. The water was put into an aluminium Coke(tm) can. The spirit burner was weighed with its cap on and then put under the can so that the tip of the flame was just touching the bottom of the can. The cap was taken off and the wick lighted as soon as possible (so that the alcohol would not evaporate). During the heating of the water, the water was stirred at a constant rate so that it would heat the water evenly and the water would heat up faster. Once the water reached 20oC above it's starting temperature (usually around 42oC), the flame of the spirit burner was blown out, the cap replaced and weighed again as quickly as possible. ...read more.

Conclusion

This meant that a fast burning spirit burner would use more alcohol to heat the water up by 200C than a slow burner. This could be corrected by using the same spirit burner for every alcohol. * At the bottom of the can was carbon, which showed incomplete combustion and insulated the water from the heat of the burner. This meant that not all of the alcohol was being combusted to produce heat, carbon dioxide and water, some was also producing carbon. This also meant that an insulator had been formed and results after the first experiment would be inaccurate as a result. This could be corrected by using a different can for each experiment so there would be no insulating carbon layer at the start. * Alcohol was still lost after the initial weighing and before the final mass weighing through evaporation, as sometimes, due to disorganisation, the wicks were not lighted immediately after the mass reading had been taken. This meant that some of the results were inaccurate. Ensuring organisation and keeping a ready supply of spills and a burning Bunsen on the table could correct this. * Stirring was not entirely accurate due to human error. This meant that when the water was being stirred faster the water heated up faster and less alcohol was combusted than should have been. This could be corrected next time by not stirring the water at all (but this would take a long time for the water to heat up) or using a machine to stir the water at a constant speed. * Some of the heat from the burner was lost to the surroundings. This cannot be corrected. * * * * Chemistry coursework DeveshPAREKH 1 ...read more.

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