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Investigating The Heat Of Combustion Of Alcohols.

Extracts from this document...

Introduction

Arunesh Kumaravel                            Chemistry Coursework

Investigating The Heat Of Combustion Of Alcohols

Aim:

 To investigate the amount of heat given out by burning alcohols. I will do this by working out how much heat energy is produced per gram of alcohol. This will then be converted into heat energy per mole of alcohol.

Introduction:

Alcohols are part of a HOMOLOGOUS SERIES. The general formula for an alcohol is CnH2n+1OH. All alcohols have hydroxide ions, which acts as the functional group. The functional group is the group of atoms responsible for the characteristic reactions of a compound. Out of all the alcohols, ETHANOL is the most important. It is produced by fermentation or by the hydration of ethene. It will be interesting to see how ethanol burns with a flame. However I will also be testing to see how well methanol, propanol and pentanol burns with a flame.

Hypothesis:

 I predict that all the reactions will be exothermic. This is from the knowledge I already have about the combustion of alcohols. I have worked out from using bond energies that in the combustion of alcohols, energy is released. With the alcohols a reaction can be written showing the combustion of the alcohol. I will go through each alcohol we used and make a prediction about the amount of energy it will give of using bond energies. For methanol the equation would be:

Methanol + oxygen                carbon dioxide + water + energy

CH3OH + 3/2O2 (g)                               CO2 (g) + 2H2O (g) + energy

We can see that there are a certain amount of bonds that need to be broken and a certain number that are made. I will now analyse these bonds.

METHANOL-: C-H bonds- 435kJ per mole

H-O bonds- 464 kJ per mole

C-O bonds- 358 kJ per mole

OXYGEN-:   O-O double bonds- 497 kJ per mole

...read more.

Middle

 oC. However all the other factors will be attempted to be controlled to the best of our abilities.

VOLUME OF WATER-

To make sure that the volume of water is constant throughout the experiment, we will accurately measure out 50mm of water in the measuring cylinder making sure the same person measures out the water each time.

LENGTH OF WICK-

This is difficult to control since the volume of alcohol in each spirit burner will decrease as the experiment goes on since other groups will be using the spirit burner. This means that the length of the wick may vary. This may cause anomalies in our experiment but hopefully we can still obtain as accurate results as possible.

BUILD UP OF SOOT-

To make sure that there is as little amount of soot on the copper calorimeter as possible we will clean it after every test thoroughly. Water will be run over the copper calorimeter and will be dried before we test the next alcohol. This is to ensure that as much heat energy as possible heats the water to ensure our experiment is as fair as possible.

DISTANCE OF COPPER CALORIMETER-

We must keep the distance of the copper calorimeter from the spirit burner the same after each experiment. This is to ensure that as little heat energy as possible is lost or not used to heat the can. This also ensures that all the alcohols have equal distance from the copper calorimeter so the same amount of heat energy is lost to the surroundings. I will keep the same distance by keeping the boss in the same place on the retort stand at all times and only loosening the clamp to take out the copper calorimeter to clean.

...read more.

Conclusion

Improvements:

We could have improved the experiment by concentrating on how to lower the heat loss. Having a lower temperature change could have done this. This would have lowered the heat loss since heat loss is proportional to temperature change. This means that the higher the temperature change, the more heat lost to surroundings. Therefore if we had a lower temperature change, less heat energy would have been lost to the surrounding.

If we had found out the heat capacity of the copper calorimeter, we could have used this value to work in the formula to find out the amount of heat absorbed by it. This value would have been part of the heat energy given of by the alcohol even though some of it would have been passed on to the water. If we had taken this into account, our results would have been a lot more closer  to out predicted values.

We could have also had an evaporation lid with a hole in it to allow the thermometer to go through it. This would have lowered heat escaping through convection or evaporation lid.

We could have also made sure that we have draught shield all the way round the experiment. This would have made sure that no draughts can affect our experiment and thus this would lower heat loss.

The experiment could have been repeated more times to ensure that we obtain a better average and thus we would obtain a smooth straight line.

Extension:

We could have taken the experiment further in a variety of ways. Below I have listed a few ways:

  • Compare the energy produced by alcohols to energy produced by alkanes.
  • Do the experiment with a larger variety of alcohols, with more carbon atoms.
  • Tested the alcohols against different volumes of water.

...read more.

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