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An investigation into the heat of combustion of alcohol's

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Introduction

Wednesday 19th June 2002 / Jonathan Hayes / 10T An investigation into the heat of combustion of alcohol's AN INVESTIGATION INTO THE HEAT OF COMBUSTION OF ALCOHOL'S 1 PLANNING 1 INTRODUCTION 1 APPARATUS 1 METHOD 2 DIAGRAM 2 HOW I WILL MAKE MY EXPERIMENT A FAIR TEST 2 SAFETY 2 PRELIMINARY WORK 2 RESULTS 3 WHAT I HAVE FOUND OUT FROM MY PRELIMINARY WORK 3 MY RESULTS TO MY EXPERIMENT 3 RESULT AVERAGES 4 ANALYSIS OF RESULTS 4 THE ENERGY TRANSFERRED TO THE WATER. 4 ENERGY TRANSFER PER GRAM OF ALCOHOL 5 THE HEAT OF COMBUSTION PER MOLE 5 MY GRAPH 6 CONCLUSION 7 EVALUATION 7 HOW I COULD MAKE MY EXPERIMENT MORE RELIABLE. 7 ARE MY RESULTS ACCURATE? 8 WHAT I WOULD CHANGE IF I REPEATED THIS EXPERIMENT. 8 Planning Introduction I am trying to determine the heat of combustion for the first five alcohols, which are; ethanol, propanol, butanol, pentanol and hexanol. I am trying to determine whether the amount of Carbon atoms on the molecule affects the heat energy given out by the molecule when burned. I believe that as the size of the molecule increases and the chain of carbons grows longer, then the heat energy given out will increase. I think that this is because when the molecule bonds are broken then they take in energy and then when the bonds are being made they give out energy. In a large molecule, more bonds are made so more energy is given out. Apparatus * Clamp stand * Clamp * Copper calorimeter * Spirit burner * Matches * Thermometer * Ruler * Metal safety tray * Top pan balance (digital scales) ...read more.

Middle

I now have my results and I now need to calculate the energy transferred to the water by each alcohol. And also the energy transferred per gram of each alcohol. The energy transferred to the water can be calculated using the equation; Energy transferred = mass of water (g) X Specific Heat Capacity X Rise in Temperature (?C) This means that all of the results will be exactly the same because in each experiment I used the same mass of water (100g), the specific heat capacity of water which is always 4.2J/g and the temperature rise in each experiment which is always 60?C. If I now put these numbers into the formula I get: Energy transferred = 100g x 4.2J/g x 60?C = 25 200J The answer is 25 200 joules but that number is a little big to work with so I can turn it into 25.2KJ instead. Energy Transfer per gram of alcohol I am now ready to work out my energy transfer per gram of alcohol. This is done by dividing the energy transferred to the water (25.2KJ) by the average mass of alcohol used to give the answer of the energy transfer per gram of alcohol in KJ/g. Alcohol: Energy transferred to water (kJ) Energy transfer, Average Mass of alcohol used Energy transfer per gram of alcohol (kJ/g) Ethanol 25.2 7.91 3.19 Propanol 25.2 6.24 4.04 Butanol 25.2 5.285 4.77 Pentanol 25.2 5.425 4.65 Hexanol 25.2 3.555 7.09 The Heat of combustion per mole I now need to calculate the heat of combustion per mole. ...read more.

Conclusion

There is one anomalous result and that is Hexanol. I think that the wick could have been slightly higher on the Hexanol spirit burner, which could have meant that less heat was lost to the surroundings and it was more efficient than the others. As more energy was out into the water in a shorter space of time, it reached the desired temperature rise of 60?C more quickly and used a lower mass to do this. Therefore giving a higher result. I think that Hexanol should have been at around the 500-kJ/mole mark for its heat of combustion. That is only an estimate and further results would have to be taken to support this. I think that the evidence is definitely reliable enough to support the conclusion that, the more Carbon atoms in an alcohol, the higher the heat of combustion. What I would change if I repeated this experiment. This experiment could be improved but it would take better apparatus. I could try to eliminate most of the factors that I described that were disrupting my results. To do this I would need a large bell jar that I could set my experiment up in. The bell jar would stop draughts getting to the flame and prevent energy loss to the surroundings. I could also pump air into the bell jar, which would provide a constant supply of oxygen. This would encourage a more efficient burning process and prevent soot forming on the calorimeter and preventing heat conduction by being an insulator. I could also weigh my water to be more accurate and cut my wicks to the same size. All of this would improve the quality and reliability of my results and my experiment in general. 1 1 ...read more.

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