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The Combustion Of Alcohol

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Introduction

Alexandru Apetrei 11H The Combustion Of Alcohol Background information In order to make a proper assessment of the experiment I have gathered background information about the reactions and consequences of reactions which are below. Key Points: * The breaking of bonds is endothermic, and the making of bonds is exothermic. * The difference between the two decides whether a reaction is exothermic or endothermic. I can use this to calculate the theoretical change in energy, by using the given values, of the energy required to break certain bonds. Chemical Bond Energy (KJ/Mol) : Type of chemical bond Energy required to break or make bond(KJ/Mol) C-H , Carbon Hydrogen single bond 413 O--O , Oxygen Oxygen double bond 497 O-H , Oxygen Hydrogen single bond 464 C--O ,Carbon Oxygen double bond 745 C-O , Carbon Oxygen single bond 358 C-C , Carbon Carbon single bond 346 Key Ideas About water : * 1 cm3 of water = 1g of water * Heat Transferred = Mass of Water(in Kg) X Temperature Rise(In KJ) X 4.2(in *C) Variables Involved: ==> Type of Alcohol (Independent Variable) ==> Size of Container ==> Volume of water ==> Type of container ==> The amount of carbon soot left on the container ==> Volume/Mass of alcohol ==> Time ==> Distance between wick and container ==> Boss & clamp ==> Starting temperature of water Making sure it is a Fair Test: Type of Alcohol (Independent Variable): If we increase the number of carbons in the chain after Methane we make space for another Oxygen Hydrogen bond to go in. ...read more.

Middle

3712 C-O Broken 2 358 716 O-H Broken 2 464 928 O- -O Broken 3 497 1491 Total = Energy of bonds broken - energy of bonds made Total = 5613 - 6692 = -1079J Equation: 2CH3OH + 3O2 = 2CO2 + 4H2O - 1079J Total energy for only one molecule: 539.5 Ethanol: Bond Type Made or Broken Numbers Of Bonds 1 Bond Energy Total Bond Energy C-C Broken 1 346 346 C-O Made 4 745 2980 C-H Broken 5 413 2065 O-H Made 6 464 2784 C-O Broken 1 358 358 O-H Broken 1 464 464 O--O Broken 3 497 1491 Total = Energy of bonds broken - energy of bonds made Total 4724 - 5764 = -1040J Equation: C2H5OH + 3O2 = 2CO2 + 3H2O - 1040J Propan-1ol: Bond Type Made or Broken Numbers Of Bonds 1 Bond Energy Total Bond Energy C-C Broken 2 346 692 C-O Made 12 745 8940 C-H Broken 14 413 5782 O-H Made 16 464 7424 C-O Broken 2 358 716 O-H Broken 2 464 928 O--O Broken 9 497 4473 Total = Energy of bonds broken - energy of bonds made Total 12591 - 16364 = -3773J Equation: 2C3H7OH + 9O2 = 6CO2 + 8H2O -3773J Total energy for only one molecule: 1540.5J Butan-1ol: Bond Type Made or Broken Numbers Of Bonds 1 Bond Energy Total Bond Energy C-C Broken 3 346 1038 C-O Made 8 745 5960 C-H Broken 9 413 3717 O-H Made 10 464 4640 C-O Broken 1 358 358 O-H Broken 1 464 464 O--O Broken 6 497 ...read more.

Conclusion

Also during the experiment, some of the water will have evaporated, thus the water mass/temp reading will be altered. I feel that this experiment could have been improved by using a wider range of alcohols such as hexanol and heptanol. This would give a better graph reading and a wider range of results to support a firm conclusion. If I had started below room temperature, so that the amount of energy gained, from room temperature might equal the energy lost at temperatures higher than room temperature. Next time reducing heat lost would be my main priority. Improving insulation techniques would be a valuable asset in obtaining the most reliable data I could. Another error is that of incomplete combustion. Complete combustion occurs if there are lots of oxygen atoms available when the fuel burns, then you get carbon dioxide (carbons atoms bond with two oxygen atoms). If there is a limited supply of oxygen then you get carbon monoxide (each carbon atom can only bond with one oxygen atom). This is when incomplete combustion has occurred. This is so because the carbon monoxide could react some more to make carbon dioxide. If the oxygen supply is very limited then you get some atoms of carbon released before they can bond with any oxygen atoms. This is what we call soot. Since heat is given out when bonds form, less energy is given out by incomplete combustion. So this is why it affects the outcome of the experiment. To overcome this problem, I would have to make sure a sufficient supply of oxygen was involved in the reaction. ...read more.

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