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A Comparison of the Energy Released When Different Fuels are burned.

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Introduction

A Comparison of the Energy Released When Different Fuels are burned Aim: To compare and test how well Methanol, Ethanol, Propanol, Butanol and Pentanol will burn and how much energy will be produced. Introduction: Alcohols have the general formula CnH2n+1OH. These atoms are generally part of a homologous chain. I have been set a task to investigate the burning of alcohols. As the structure shows, the alcohols will burn in oxygen to form carbon dioxide and water vapour. Alcohol + oxygen carbon dioxide + water Using this equation I will calculate the bond energy formed, bond energy broken and the H (which will tell me what type of reaction it will be). The five alcohols that will be burned are: Methanol, Ethanol, Propanol, Butanol and Pentanol. Calculations: * Methanol Methanol + oxygen carbon dioxide + water CH3OH + 11/2O2 CO2 + 2H2O Sum of bond energies broken: 3(H-C) 3 x 413 = 1239 (C-O) 358 = 358 (O-H) 464 = 464 11/2(O=O) 11/2 x 498 = 747 + 2808 KJ/mol Sum of bond energies formed: 2(O=C) 2 x 805 = 1610 4(O-H) 4 x 464 = 1856 + 3466 KJ/mol H = Sum of �E broken - sum of �E formed = 2808 - 3466 = -658 KJ/mol H is negative; therefore the reaction will be exothermic. ...read more.

Middle

and then will combust later, making this experiment an exothermic reaction. Therefore the long chains of hydrocarbons produce more energy than smaller chain molecules as the long chain breaks in to smaller hydrocarbons meaning theirs more, making the boiling point decrease, which makes them more flammable, less viscous, and more volatile. Therefore I would expect that when the alcohol's is being burned and producing heat energy, carbon dioxide, and water will be produced meaning the alcohol would lose some mass which would evaporate into the air. I therefore predict that when there is a longer chain of hydrocarbons than another alcohol, it would produce more heat than the other alcohol meaning it would have a higher reading each minute compared to a smaller chain of hydrocarbons, which could mean that the smaller hydrocarbons combust quicker then longer hydrocarbons as their less volatile. Apparatus: * Spirit burners containing the different alcohols * Measuring cylinders * Thermometer * Balance (measuring to 2dp) * Boiling tube * Stop clock * Matches * Clamp and stand * Water Diagram: Plan: First of all; the container of the alcohol will be measured including the snuffle using a balance, and the mass will be recorded. ...read more.

Conclusion

These are the results I obtained, after burning three alcohols. Temperature of water/�C Volume of water/ml Before After Difference Before After Difference Butanol 21 100 79 20 19 1 Ethanol 21 106 85 20 17 3 Propanol 27 103 76 20 18 2 Flame description Appearance of boiling tube Distance from wick Butanol Half blue, half yellow, 5cm high Black, sooty bottom part 2cm Ethanol Yellow, 5cm high Black, sooty bottom part 2cm Propanol Bright yellow, 3.5cm high Very sooty, rapidly 2cm Looking at my preliminary results I decided to also change the time of when I will record the temperature gained by the water, from 3 minutes, to 2.5 minutes, as the results I got in my preliminary results had a great change in temperature. I have also decided to change the distance from the wick. This is because the flame heights of the alcohols varied therefore the boiling tubes were dangerously in the flame. Therefore I decided to not keep the distance from the wick constant, and keep the boiling tube as high so that on the tip of the flame touches the boiling tube. Method: The alcohol was measured using a balance. Heat given out = mass of water x 4.2 x change in temperature Chemistry coursework Shraddha Patel GCSE Page: 1 ...read more.

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