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In this experiment our aim is to find out if the number of carbon atoms or bonds affects the energy output of 4 different alcohols when they are ignited.

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Introduction

Chemistry Coursework Introduction In this experiment our aim is to find out if the number of carbon atoms or bonds affects the energy output of 4 different alcohols when they are ignited. To investigate this we will use 4 different alcohols (Ethanol, Methanol, Propanol and Butanol) in an experiment in which we will ignite each of the 4 alcohols measuring the energy given off with a calorimeter. The 4 alcohols have a different number of carbon atoms in each molecule so any patterns or trends will tell us that the number of carbon atoms does affect the engery given off. Prediction An accurate prediction can be made by using bond energy tables because of the fact that our experiment is based on the number of bonds in a molecule. If these calculations produce a negative number then we know that energy has been realesed through the reaction and that it is an exothermic reaction. If the number is positve then energy has been consumed and it would have been an endothermic reaction. I will now demonstrate these reactions through the following bond energy tables. The final kJ/mol readings should show weather the reaction is exothermic or endothermic. I will base my prediction on the results of these tables. Methanol CH3OH H | H - C - O - H + 3(0=0) --> 2 (0 = C = 0) ...read more.

Middle

463 10574 6 ( O = O ) 6 x 496 8551 ?H = 8551 - 10574 = - 2023 = 2023 kJ/ mol No . of Alcohol Carbon ?H Atoms kJ/mol Methanol 1 535 Ethanol 2 1031 Propanol 3 1527 Butanol 4 2023 After working out the ?H/mol of each alcohol and taking into account the number Carbon atoms/mol in each alcohol, I predict that butanol will give off the most energy. My calculations also show that the more carbon atoms there is the higher the ?H. Plan Apparatus used : .Spirit Burner .Thermometer .Calorimeter .Clamp Stand .Digital Scale We carried out a preliminary experiment in order to check our methods were correct. We filled a calorimeter with 100g of water and then placed the calorimeter 3cm above the spirit burner containing the alcohol being burned. We thought that 3cm was the correct height above the flame because it was the optimal height were we would get the best results, it was not too high to a point where the flame would have a reduced effect on the calorimeter or not too low to a point where the flame may be choked by the calorimeter. We chose to use 100g of water because 100 is a whole number so it would make our calculations easier and because we feel that 100g is an optimal weight for this experiment. ...read more.

Conclusion

I feel that they do agree with my prediction that the more carbon atoms there are the higher the enthalpy of combustion. I am quite happy at our planning of our experiment. I do feel that our control variables (height of calorimeter, temp rise and weight of water) were controlled and chosen quite correctly. Our calculations also seemed to be correct because they gave us sensible outcomes. However I do feel that we could have been more careful in making sure that our experiment wasn't effected by draughts and other things that have effected our outcome. We must take into account that our experiment was carried out in a room where there was a lot of people moving (causing draughts in their wake), a lot of people using spirit burners which would have effected the room temperatures. I do think that our results would have been more accurate if the experiment was performed in a room with minamal effecting factors to the experiment. On the whole I do think that our experiment has produced results that can be used to support my conclusion. I do feel that to help prove my prediction further I could perform more detailed experiments with different alcohols. I could use a more accurate type of calorimeter (eg a bomb calorimeter). I could use better digital scales and other measurement instruments. I could also use a wider range of alcohols with varying numbers of carbon atoms. All this would enable me to come up with more accurate results which would support a stronger conclusion. ...read more.

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