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Comparing the Enthalpy changes of Combustion of different Alcohols.

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Introduction

Comparing the Enthalpy changes of Combustion of different Alcohols An experiment was given to us to do in class. We looked at 5 different alcohol's that were given to us to test. These were the following alcohol's given: methanol, ethanol, propan-1-ol, propan-2-ol and butan-1-ol. We had to burn each alcohol completely in oxygen until the temperature recorded at the beginning was 20oc higher than it started it off as. Then everything was re-measured, which would help with the following calculations to work out the enthalpy changes of combustion for each alcohol, which will then be compared for a conclusion. Analysis I will first do my result table showing all the values I found after doing the experiment. I did the experiment twice in the time we had in class. So I have three results tables. Two contain the results I got from the two experiments and the third shows the average I got from the results. I will use the third table to calculate the enthalpy changes of each alcohol, as this table of results will contain the most accurate results. Results Table 1: Results from the experiment the first time round. FUEL METHANOL ETHANOL PROPAN-1-OL PROPAN-2-OL BUTAN-1-OL Water (g) 192.8 190.3 194.5 195.8 196.6 Mass of burner and alcohol before the 117.3 163 139.3 120.4 116.8 experiment. (g) Mass of burner and alcohol after the 115 160.6 138.3 119 115 experiment. ...read more.

Middle

12+16+(4x1)=32g * Number of moles of fuel used: 1 mole = 32g (1/32) x (mass of fuel used) = (1/32) x 2g = 0.0625 moles (4.d.p.) * Energy transferred by this number of moles: (Look above at bullet point number 4) 192.75g x 21oC x 4.2J = 17000.55J * Energy transferred by 1 mole of fuel: 0.0625 moles = 17000.55J 1 mole = (17000.55/0.0625) = 272008.5J (1.d.p.) * Enthalpy Change of Combustion: (272008.5J/1000) = 272.0088 (1.d.p.) = -272.0Kjmol-1 Ethanol * Mass of water used: 192.2g * Temperature rise in water: 20.75oC * Mass of fuel used: 1.95g * To work out the amount of heat absorbed by the water in the experiment we do the following: (mass of water) x (temperature rise in water) x 4.2J 192.2g x 20.75oC x 4.2J = 16750.23J (2.d.p.) * Molecular Formula: CH3CH2OH * Structural Formula: H H H C C O H H H * Mass of 1 mole of fuel: (C:12; O:16; H:1) (2x12)+16+(6x1)=46g * Number of moles of fuel used: 1 mole = 46g (1/46) x (mass of fuel used) = (1/46) x 1.95g = 0.0424 moles (4.d.p.) * Energy transferred by this number of moles: (Look above at bullet point number 4) 192.2g x 20.75oC x 4.2J = 16750.23J * Energy transferred by 1 mole of fuel: 0.0424 moles = 16750.23J 1 mole = (16750.23/0.0424) = 395052.6J (1.d.p.) * Enthalpy Change of Combustion: (395052.6J/1000) ...read more.

Conclusion

* Molecular Formula: CH3CH2CH2CH2OH * Structural Formula: H H H H H C C C C O H H H H H * Mass of 1 mole of fuel: (C:12; O:16; H:1) (4x12)+16+(10x1)= 74g * Number of moles of fuel used: 1 mole = 74g (1/74) x (mass of fuel used) = (1/74) x 0.70g = 0.0095 moles (4.d.p.) * Energy transferred by this number of moles: (Look above at bullet point number 4) 194.25g x 19.75oC x 4.2J = 16113.0375J * Energy transferred by 1 mole of fuel: 0.0095 moles = 16113.0375J 1 mole = (16113.0375/0.0095) = 1703378.3J (1.d.p.) * Enthalpy Change of Combustion: (1703378J/1000) = 1703.37825 (1.d.p.) = -1703.4Kjmol-1 Now that I have worked out all the enthalpy changes of the alcohol's above I will put them in a table so I can easily compare them for each alcohol. This will be Table 4. Table 4: Enthalpy Changes of Combustion of all the alcohol's tested and the amount of heat the water absorbed in each experiment. FUEL METHANOL ETHANOL PROPAN-1-OL PROPAN-2-OL BUTAN-1-OL Amount of heat absorbed 17000.55 16750.23 17137.26 16113.04 15934.8 by water in the experiment. (2.d.p.) (2.d.p.) (2.d.p.) (2.d.p.) (2.d.p.) (Joules) Enthalpy change of -272.0 -395.1 -1206.8 -1381.1 -1703.4 combustion. (1.d.p.) (1.d.p.) (1.d.p.) (1.d.p.) (1.d.p.) KJmol-1 Now I am going to use all the information above to help me investigate how and why the enthalpy changes of combustion of alcohols is effected by their molecular structure. Here is the molecular structure of Methanol. I worked out that the enthalpy change of Combustion of Methanol is -272.0Kjmol-1. H H C O H H Amara Amjad ...read more.

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