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Experiment to measure the enthalpy change of combustion for hexane and methanol

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Introduction

TASK 1 (a) Carry out the activity on measuring the enthalpy change of combustion for hexane and methanol and calculate your result. In this experiment i will burn the fuel methanol (this is an alcohol which can be used as an alternative fuel) and arrange the apparatus to get most of the energy transferred to the water. Method * Firstly i will pour 200cm3 of cold water in a copper calorimeter then i will use a thermometer to record the temperature of the water. * By using clamp stands and bosses i will support the calorimeter over the spirit burner containing the methanol fuel * I will arrange a suitable system which will stop any heat from escaping to the surrounding by placing heat mats all around the apparatus. * Before starting the experiment i will record the weight of the spirit burner and record my results * Now i will place the burner under the calorimeter and light it, i will be stirring the water using the thermometer as its being heated * I will continue doing this until the temperature has risen about 15-20oC. ...read more.

Middle

= ?H-658 KJ/mol-1 Mass of 1 mole of methanol = 32g (C=12+H=(1x4)+O=16) Mass of fuel burned= Average/Mass --> 0.658 / 32 = 0.0205625 Energy Transferred by 1 Mole of Fuel = Mass of Water (g) x Change in Temperature x 4.18J (this is the energy required to raise the temperature of 1g of water by 1oC) = 50g x 8.32 x 4.18J = 1738.88J Heat given out by 1 mole of methanol = 1738.88 / 0.0205625= -84565.59J --> -84.5656 KJ/mol-1 Describe the terms endothermic and exothermic in terms of bond breaking and bond forming When a chemical reaction takes place bonds are broken in the reactants this is known as endothermic as energy is absorbed from the surroundings to break these bonds you can see this happening in the above ENDOTHERMIC REACTION the reactants are below the products meaning that the reactants need more energy from the surrounding the overcome the activation barrier and less energy is given out. The bonds of the products are weaker than those of the reactants and this is seen as a + (plus) ...read more.

Conclusion

The main error which could have given me invalid results was the calorimeter as when it gets heated it also gets covered in soot & heat loss 4. Also as the spirit burner is covered up there is another factor which could affect the experiment which is the oxygen levels as if they drop incomplete combustion. To improve the practical i could use a different copper calorimeter each time or rinse off the black soot. Procedural Errors: A Weighing balance was used to measure the mass of the spirit burner before and after the experiment the balance was to 2 decimal places Methanol before the experiment Percentage error = 0.005 x 100 = 0.0225% 22.83g Methanol after the experiment Percentage error = 0.005 x 100 = 0.0225% 22.212g I also used a measuring cylinder to measure the amount of water i used 2 x 100cm3 measuring cylinder to get 200cm3 i ensured lots of accuracy by looking at the bottom meniscus while measuring to produce more accurate reading i could have used pipette. ?? ?? ?? ?? ...read more.

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