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EN4 Determination of Enthalpy Change of Combustion

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Introduction

1) Title: EN4 Determination of Enthalpy Change of Combustion 2) Aim/Objective: To find out the calibration factor of propan-1-ol by burning a measured mass of it in a spirit lamp and use the calibration factor to find out the enthalpy change of combustion of other alcohols (ethanol, butan-1-ol, pentan-1-ol, hexan-1-ol). 3) Results: (1) Calibration of the Calorimeter Molar mass of propan-1-ol 60 Initial mass of spirit lamp + propan-1-ol (m1) 262.63 g Final mass of spirit lamp + propan-1-ol (m2) 261.53 g Mass of propan-1-ol burnt (m1-m2) 1.1 g Number of moles of propan-1-ol burnt (n) 0.01833 mol Initial temperature of calorimeter 17.8? Final temperature of calorimeter 37.8? Temperature raised (?T) 20? Standard enthalpy change of combustion of propan-1-ol ?HC [propan-1-ol (l)] * n -2017kJ/mol Heat energy released during the experiment, E = ?HC [propan-1-ol (l)] * n 36.978kJ Heat energy required for the calorimeter to rise 1 K = E/?T = C (Calibration factor) 1.849kJ/mol (2) Experimental data of other alcohols Ethanol Butan-1-ol Pentan-1-ol Hexan-1-ol Molar mass 46 74 88 102 Initial mass of spirit lamp + alcohol (g) ...read more.

Middle

Such great error should be due to the errors listed below, due to the alternation of experimental factors in different cases. It was essential for the volumes of water in the aluminum can to be the same when performing the experiments of different alcohols. 200ml of tap water was used in each case. However, if the volume of water used was not 200ml, the enthalpy change calculated would be slightly different. For instance, if the volume of water was larger, maybe because some water was remained in the can, a greater amount of heat would be required to heat up the water to a certain amount. As a result, more alcohol in the spirit lamp would be used, giving a smaller enthalpy change of combustion of that alcohol. In the tests after the first one, as some water was left in the can, this can explain why the enthalpy changes calculated are so high. During the experiment, none precautions were taken to prevent heat loss to the surroundings, because it was assumed that the heat loss to the surroundings from the calorimeter was constant when burning the different alcohols. ...read more.

Conclusion

As a result, the calculated mass of alcohol used was larger than the actual one and so the enthalpy change calculated was smaller than the literature value. Most importantly, the standard enthalpy change of combustion of propan-1-ol was calculated in an experiment of standard conditions. However, for the first experiment, using propan-1-ol to calculate the calibration factor, the conditions were not standard. This could give a reason for the difference. Seeing these errors, it was normal to find the calculated values of the enthalpy changes to be different from the literature values. The difference of the enthalpy changes of adjacent pair of alcohols was found to be roughly constant, for the case of the literature value. This is because the covalent bond of alcohols with higher carbon number is greater and so more energy is required to break the bond. Tracing such difference, the enthalpy change of combustion of other alcohols can be predicted, for example, adding about 650kJ/mol for each next alcohol. 6) Conclusion: The enthalpy changes of combustion of the alcohols were found to be -1374kJ/mol, -1683kJ/mol, -3427kJ/mol, -4601kJ/mol for ethanol, butan-1-ol, pentan-1-ol and hexan-1-ol, under room conditions of 774mmHg and 19.0?. ?? ?? ?? ?? Yu Wing Yee 6A(30) - 1 - ...read more.

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