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# Comparing the enthalpy changes of combustion of different alcohols

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Introduction

Unit 1.4b Aim: Comparing the enthalpy changes of combustion of different alcohols Introduction: I am going to investigate the difference in enthalpy of combustion for a number of different alcohols. My aim is to find out the best fuel out of the five alcohols. I will calculate the value for enthalpy change by burning different fuels to heat a specific amount of water using the fact that 4.2J of energy are required to raise the temperature of 1g of water by 1�C. I will also produce a wide range of results and compare them to calculate their enthalpy change of combustion. Background information: The enthalpy change of combustion is the energy transferred to and from the surroundings at a constant pressure, when one mole of fuel burns completely. The symbol is ?H. The chemical reactions that release energy to their surroundings are called exothermic and the energy that transferred to them from the surroundings is called endothermic. ?H = ?H products - ?H reactants The units are kilojoules per mole (kJmol-1) Exothermic Ref: http://www.s-cool.co.uk/a-level/chemistry/chemical-energetics/revise-it/enthalpy-changes Exothermic reactions are more common. An example of exothermic reaction is: photosynthesis in plants where the energy comes from the sunlight. ...read more.

Middle

* Then, the spirit burner was place under the copper can which were used to burn. * A suitable draft exclusion system was arranged to reduce heat loss. * The wick was lighted to heat the water. * While heating the water, the thermometer was used to stir the water to get an accurate temperature of the water. * The mercury thermometer was being observed till the temperature was risen by 15�C to 20�C. * As soon as the temperature was risen by 15�C to 20�C, the spirit burner's lid was placed on the flames to extinguish the burner. * When the temperature reached its highest point, the temperature was recorded. * The mass of the alcohol was placed on the electronic balance to record the final mass. * The experiment was repeated in the same way for the five alcohols * At the end of the experiment, all the results was recorded on a suitable table Results: ALCOHOLS MASS (INITIAL) MASS (FINAL) TEMPERATURE (START) TEMPERATURE( FINAL) Ethanol 1. 232.35g 2. 231.51g 231.51g 230.64g 18.5�C 13.5�C 33.5�C 28.5�C Methanol 1. 151.25g 2. 149.56g 149.56g 148.16g 15.5�C 16.0�C 31.0�C 33.0�C Butan-1-ol 1. ...read more.

Conclusion

Procedure error 2. Measurement error 1. Procedure error Procedure error can occur in the procedure of the experiment, the errors are mainly while transferring solution, the volume of the solution can decrease which would not be accurate for the final record. Another one is the reaction time for extinguishing the flames when the temperature reached by 15�C to 20�C, as a rise on temperature makes a big difference in the result. How to improve it? The only way to improve the procedure error is to avoid transferring water in many beakers. In addition, extinguish the flames as soon as possible will receive an accurate temperature of the alcohols. 2. Measurement error Measurement error can occur while taking the reading from the measuring cylinder as the reading should be rounded up to the nearest � 1 cm3, the thermometer should be �0.5�C and the weighting scale should be rounded up to �0.005g. This can be accurate most of the time in experiment but sometime it can't be completely accurate. Another measurement error can occur if the person only does the experiment once. How to improve it? The best way to improve it is to try to be more accurate rather than rounding up to the nearest numbers sometimes and the experiment should be repeated twice or three times to be more accurate. ?? ?? ?? ?? Ahvashta Seeburrun 1 ...read more.

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This is a good description of how to test the enthalpy of combustion for a wide range of alcohols. However, there are various mistakes throughout the report to watch out for. This can actually be quite useful, as the mistakes have been highlighted by the marker , enabling you to realise which mistakes not to make yourself.

Overall, this piece of work is 3 stars out of 5

Marked by teacher Brady Smith 09/04/2013

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