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Alcohol Combustion Experiment

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Adam Franks 10BW GCSE CHEMISTRY COURSEWORK Skill Area:"P". Planning. Background information 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. We can calculate the theoretical change in energy, by using given values, of the energy required to break certain bonds. Prediction I predict that if the Mr value of the alcohol / and the number of carbon atoms is increased that the heat of combustion will increase. I predict that the heat of combustion will increase in a regular manner aswell. Equations 1C2H5OH + 3O2 2CO2 + 3H2O 1C3H7OH + 4.5O2 3CO2 + 4H2O 1C4H9OH + 6O2 4CO2 + 5H2O 1C5H11OH + 7.5O2 5CO2 + 6H2O 1C6H13OH + 3O2 6CO2 + 7H2O PREDICTING HEATS OF COMBUSTION, BY CALCULATING THEM USING BOND ENERGY VALUES. 1.) Ethanol H H H C C O H + 3O=O 2O=C=O + O H H H H Bonds Broken (ENDOTHERMIC) ?H = + Bonds Formed (EXOTHERMIC) ?H = - 5 x C-H is 5 x 413 = +2065 4 x C-O is 4 x 805 = -2065 1 x C-C is 1 x 347 = +347 6 x H-O is 6 x 464 = -2784 ...read more.


The alcohol burner was then lit. While the burner was lit the water in the small beaker was stirred. When the temperature of the water had increased to between 15� to 20�, the alcohol burner was blown out. The final temperature of the water was then found, and the final weight of the alcohol was found. To find the heat of combustion the heat change had to be found first. This found by using the equation... Heat change = mass x temperature change x S.H.C Once the heat change had been found the Heat of combustion could be found, and this was done with the equation... Heat of Combustion = -heat change x Mr Mass of alcohol burned In the equations there were two constants. These were, the mass of water (50g), and the specific heat capacity (S.H.C)(4.2). Results: Mass at start Average Mass at Start Mass at End Average Mass at End Temp of water at the beginning Average temp of water at beginning Mass of water Temp of water at the End. Average temp water at End Ethanol 133.700g 133.350g 132.91g 132.63g 18�C 18.5�C 50g 33�C 34�C 132.910g 132.35g 19�C 50g 35�C Propanol 189.797g 189.419g 189.041g 188.617g 20�C 21�C 50g 40�C 41�C 189.041g 188.193g 22�C ...read more.


The clamp, which is metal, and was touching the can will have meant some of the heat, was transferred into the clamp and stand, causing more heat loss form the experiment. In order for this experiment to be more accurate, I would have to insulate the can and the clamps, completely exclude all draughts use a better conductor other than water to heat, and use a thinner can, made of a better heat conducting material. Given that the range of the experiment was only 6 alcohols from methanol to hexanol and that the experiment was only 3 minutes, and the inaccuracies of the experiment, I would say that the evidence is not strong enough to draw firm conclusions from. If this experiment was to be done again, then all the possible sources of error mentioned would have to be counteracted and controlled, as well as using a much wider range of readings of many more alcohols, burn them for different periods of time, heat different substances other that water, investigate the other variables. I would also take many more readings so a much more accurate average could be taken. Other experiments could have been done investigating other organic compounds, such as hydrocarbons, to see if they behave similarly, and investigate them under different conditions, such as at extremes of temperature and pressure. ...read more.

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