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Investigating the enthalpy change of different alcohols

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Introduction

Investigating the enthalpy change of different alcohols Method In this investigation I am going to try to find out if there is a relationship between different lengths of alcohol chains and their combustion enthalpy change. I am going to do this by using spirit burners and a calorimeter. I will burn the fuel until it has heated up the water in the calorimeter until it is a certain temperature, then I can use the heat capacity of the water and the molecular formula of the alcohol to work out the enthalpy change. Here is my draft method: Equipment: * Aluminium can to act as calorimeter, about 10cm in diameter and able to hold about 200ml of water. * 0-50?c thermometer (or 0-110?c if 0-50?c not available). * 200ml measuring cylinder. * Spirit burners containing: Methanol Ethanol Propan-1-ol Butan-1-ol * Balance (accurate to 2 decimal places). * Clamp stand, clamp, heat mats. Set-up: Method: 1. Record temperature of water in calorimeter. 1. Weigh spirit burner and record. 1. Light spirit burner. 1. Keep burner lit until the temperature of the water is 20?c higher and record. ...read more.

Middle

This makes it more accurate as we are taking into account all the energy that is produced by the flame. * When taking the temperature of the water I will use the thermometer to stir the water as well as taking the temperature, as this will make sure that the heat is evenly distributed and therefore it will insure that the test is as fair as possible. * When it comes round to putting out the flame I will use the lid and not blow it out so that none of the fuel is lost to evaporation or anything. The lid will also be kept on until the weighing process. * I will use a mercury thermometer as this is more accurate then an alcohol one and therefore will reduce the percentage errors. * I will use the same equipment every time e.g. calorimeter, clamp, clamp stand, heat mat, thermometer. This is so that all the experiments are fair as different equipment is sometimes slightly off calibration so that at least if it is not greatly accurate it is relative so I can find a trend if there is one. ...read more.

Conclusion

In the combustion of alcohols, energy is given out at a higher ratio than it is taken in again by making the bonds, therefore the more bonds the higher the overall amount of energy given out. Here is a balanced equation for the combustion of an alcohol in a surplus of oxygen: CnOH + (n/2) O2 (n/3) CO2 + (2n/3) H2O For Methanol this is: C3OH + 1.5 O2 CO2 + 2 H2O From this I can draw these diagrams to produce a simple way of working out the bonds that are broken and made: Using the figures from data books as a reference and the number of bonds broken and made from my drawings I can show my prediction in these tables: Bond Enthalpy change (kJ mol-1) C-C 347 C-H 413 H-O 464 O=O 498 C-O 358 C=O 805 Fuel Bonds Initial energy absorbed (kJ mol-1) C-C C-H H-O C-O O=O Methanol 0 3 1 1 1.5 2808 Ethanol 1 5 1 1 3.5 4977 Propan-1-ol 2 7 1 1 5.5 7146 Butan-1-ol 3 9 1 1 7.5 9315 Fuel Bonds Final energy released (kJ mol-1) Overall enthalpy change (kJ mol-1) H-O Bottom of Form ...read more.

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