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Comparing the Enthalpy chnage of different alcohols

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Introduction

Comparing the Enthalpy Change of Combustion of Different Alcohols Aim: Enthalpy change of combustion of an alcohol is a measure of energy transferred when one mole of alcohol burns completely in oxygen. Alcohols are series of organic compounds which all contain an -OH group. The enthalpy change can be calculated by burning the fuel to heat water. It is believed that 4.2J of energy is required to raise the temperature of 1ml of water by 1�C; therefore I will use this theory in my calculations. In this investigation I will use 4 different alcohols to see how the molecular structure is linked to the enthalpy change of combustion of each alcohol. Hypothesis Relying on my previous knowledge, I predict that alcohols with a larger molecular mass will have a greater enthalpy change of combustion than the alcohols with smaller molar mass, meaning the enthalpy change will go up as the carbon number increases. I can support this hypothesis by calculating the enthalpy change of combustion of each alcohol with bond enthalpies. Hess's law states: 'The enthalpy change for any chemical reaction is independent of the intermediate stages, provided the initial and final conditions are the same for each route. The following diagram is called an enthalpy cycle. It shows a reaction where methanol that combusts in air, reacts with oxygen forming carbon dioxide and water. The diagram shows direct and indirect routes: CH3OH(l) ...read more.

Middle

Goggles and a lab coat will be worn throughout the whole experiment to keep my eyes and my skin from being damaged. I will repeat this experiment with each alcohol three times to make sure that my results are reliable. I will then record my results in a table and find an average mass used to heat the water for each. Safety: Methanol is toxic. It can irritate the eyes and mucous membranes. It can also react vigorously with oxidising materials. That is why, to keep safe, me and my fellow students should take care when handling it to make sure it's not spilled since it can react with substances. Also none of us should stay exposed to it for too long to prevent our skin, eyes and mucous membranes being irritated. Ethanol is a highly flammable chemical. Its vapour can easily catch fire; also inhalation may cause narcotic effects. That's why the spirit burners should be kept well away from naked flames and used in well ventilated classrooms. Propanol is also highly flammable and can irritate skin. Therefore, it should be kept away from any naked flames and handled with gloves on, if available. Butanol is harmful and flammable. It can easily catch fire; that is why I should take care when using it, including keeping it away from naked flames. Fair test: To make this investigation a fair test, I will make sure I control various factors. ...read more.

Conclusion

Percentage error: % error = Error x 100 Expected Result Methanol: 42/726.0 = 0.057851239 x 100 = 5.78 % Ethanol: 545.2/1367.3 = 0.398742046 x 100 = 39.87% Propanol: 728.7/2021.0 = 0.360564077 x 100 = 36.05% Butanol: 2005.8/122.2 = 16.41407529 x 100 = 1641.40% EVALUATION Looking at my investigation, I identified a number of limitations that could have led to the errors shown in my results. > Heat could have been lost to the surroundings since there was nothing around the apparatus, where draft excluders could have been placed to prevent that loss. > Since some of the alcohols have toxic fumes, the room had to bee well ventilated for our safety; that could have resulted in heat loss also. > The thermometer was left for me to read which means there could have been a slight human error. An electric thermometer could have been used; which could record the peak temperature, so no errors would be made during the reading taking. > The soot at the bottom of the calorimeter could have been acting as an insulator and stopping the efficient energy transfer. > A conclusion cannot be drawn about every alcohol because none of the isomers were used. > If I was to do this investigation again, I would take into account all the factors mentioned above and also to extend it, I would use a wider variety of alcohols(e.g. up to hexanol) and also try and do it with some isomers(e.g.Propan-2-ol). Fumilola Fawole ...read more.

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