• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
Page
  1. 1
    1
  2. 2
    2
  3. 3
    3
  4. 4
    4
  5. 5
    5
  6. 6
    6
  7. 7
    7
  8. 8
    8
  9. 9
    9
  10. 10
    10
  11. 11
    11
  12. 12
    12
  13. 13
    13
  14. 14
    14
  15. 15
    15
  16. 16
    16
  17. 17
    17
  18. 18
    18
  19. 19
    19
  20. 20
    20
  21. 21
    21
  22. 22
    22
  23. 23
    23
  24. 24
    24
  25. 25
    25

Molar Heat of Combustion of Alcohols

Extracts from this document...

Introduction

Molar Heat of Combustion of Alcohols Task: To find the molar heat of combustion of propanol, ethanol and butanol and to calculate the theoretical values using average bond enthalpies. Then to compare these to the practical values obtained from the experiments, also to predict the theoretical and practical molar heat of combustion of pentanol. Planning Background Information Alcohols: Alcohols are part of a family of compounds that are all based on a chain of carbon atoms. They can be considered derivatives of water in which the hydrocarbon atom has been replaced by a hydrocarbon chain. Alcohols all have the general formula CnH2n+1OH and which burn cleanly in oxygen or a plentiful supply of air to produce carbon dioxide and water vapour. If the air supply is reduced then they will burn to produce carbon monoxide, soot and water vapour. All Alcohols contain an oxygen atom in a hydroxyl group, meaning that the oxygen atom is joined to the hydrogen atom as well as the carbon atom. All alcohols contain at least one oxygen atom joined to a carbon atom by a single bond. Equations for the Three Alcohols: This is the formula for all alcohols: Cn H2n+1 OH The molar heat of combustion is the heat liberated when one mole of alcohol is burnt in a plentiful supply of air. These are the formulas for the combustion of the three alcohols. Butanol + Oxygen � Carbon Dioxide + Water C4H9OH + 602 � 4CO2 + 5H2O (One Mole) Propanol + Oxygen � Carbon Dioxide + Water C3H7OH + 4.5O2 � 3CO2 + 4H2O (One Mole) Ethanol + Oxygen � Carbon Dioxide + Water C2H5OH + 3O2 � 2CO2 + 3H2O (One Mole) Bond Enthalpies: Bond enthalpy is the amount of energy needed to break a chemical bond. Bond enthalpies differ with each type of bond and the exact enthalpy for a particular bond can differ. ...read more.

Middle

= Energy used by 1g. 15269.331/0.42=36355J One Mole of Butanol weighs 74g so we times the energy used by 1g by 74. 36355.55*74=2690310J Actual Experiment: We weighed the burner and the container before and after testing and recorded the temperature change. We heated the container with 25ml of water for two minutes. We weighed the water before and after so we could make the test fairer by averaging the two, the average gives a more accurate picture of the mass of water used. We used heatproof mats to stop any drafts getting to the burner as this would have made our results less accurate. We used a digital thermometer to measure the temperature at the end of the test because they are more accurate. We tried to make sure that the wick on each of the burners was the same length to make the experiments more accurate. The container is held at a set position above the burner as to make the experiment more accurate. To keep our tests fair we will have a set of variables which will remain constant throughout the test, these variables are; * The mass of water (25cm3). * The container, (different containers would have different thicknesses and sizes, therefore possibly being more or less accurate than others). * The length of the wick (0.5cm). * The distance between the container and the flame must stay the same because if there was any difference in this then the experiment would be inaccurate. * The conditions in the room should stay the same, the temperature should be around 23OC and there should be hardly any breeze as this would move the flame around which would stop the heat getting to the container. The variables that must be changed throughout the experiment are only the alcohols (and therefore the burner). The measurements we will use in our experiment are as follows: Moles (mol) ...read more.

Conclusion

The fact that we also changed containers throughout also means that we have no way of telling the weight because the ones we used are not marked. There is also the possibility that the calorimeter may have been hotter or colder than the temperature of the water. Evaluation: I was expecting our test to be very inaccurate but having looked at the different possibilities for error and at the results when including the heating of the calorimeter then I realized that it was a lot more accurate than I was expecting. Including the heating of the calorimeter the accuracy of the test peaked at 72% of the theoretical value that we worked out using the bond enthalpies. This was for butanol. We could have easily improved our test but this may not have yielded more accurate results. The biggest mistake we made throughout was not to mark our containers, this means that we may well have used containers with different masses throughout. We also did not thoroughly clean out our apparatus and containers beforehand. This means that the containers we used could well have had a covering of dirt and carbon therefore reducing conduction. Overall I think that we could have improved the accuracy of the test by reducing human error but this may not have increased the accuracy of our data. The climate and outside conditions played a large part in all of our results and there is no way to control this in the circumstances. The electrons within the alcohol molecule are shared therefore it has covalent bonds as opposed to ionic ones. Each atom within the molecule has a full outer shell of electrons from sharing with other atoms; this makes the molecule very stable. Each step-up in the group of alcohols adds two carbon-hydrogen bonds, a carbon-carbon bond, an oxygen=oxygen bond and half a carbon=carbon bond that are available for combustion. Therefore, there is a net energy gain every time. This means that the additional energy added will be the same each time. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Organic Chemistry section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Organic Chemistry essays

  1. Marked by a teacher

    What an ester is, how it is made, examples of esters, animal testing issues ...

    4 star(s)

    Evaluation of experiment two This experiment could have also been more reliable because we could have repeated the experiment, just in case it was anomaly. Also, it could have been more valid as I could have been more accurate in the amount of hot water added into the beaker or

  2. Comparing the heat energy produced by combustion of various alcohols

    The flame size changed due to the type of alcohol; hence it was a different distance away from the beaker each time. Conclusion The equipment that I used in this experiment was very inaccurate because heat is a bad way of transferring energy without any loss of it.

  1. Investigating the Combustion of Alcohols

    * Thermometer, 10-50 �C in 0.1�C intervals to measure the temperature rise of the water * Heat proof mats to act as heat (drought) shields to prevent heat loss and exclude draft which may interfere with the experimental procedure since it may extinguish the flame.

  2. Find out the heat of combustion in the five fuels; Methanol, Ethanol, Propanol, Butanol, ...

    which is where the heat energy for the reaction stored. Methanol will raise the temperature of the water the least, because it's got the least amount of intramolecular bonds, there fore it is weaker and allows the heat to break the bonds up more quickly and easily.

  1. How Does The Increase In The Length Of The Carbon Chain Affect The Energy ...

    * Note the starting temperature of the water from the thermometer and then light the alcohol burner. * Keep checking the rise of temperature on the thermometer throughout the experiment. * Additionally throughout the experiment, hold on to the thermometer and stir the water around making sure that it does

  2. Titration experiment - write up

    I used distilled water to clean my conical flask. After filling my burette I wiped it clean with a tissue so that readings could be made accurately and no spillages into my conical flask occurred as this would have altered the concentration, hence, corrupting my results. The apparatus used have percentage errors these were calculated so that they are accounted for and my results are as correct as possible.

  1. Investigating the energy released from burning different alcohols.

    Though the curve is slight, it is still apparent, I had based my hypothesis on the line in the graph displaying the theoretical heats of combustion. This proved to be wrong as the experimental values plotted on a graph were in a gradual curve.

  2. To measure and compare the enthalpy change of combustion for four different types of ...

    Doing this will help increase the accuracy of the results. Prediction It is predicted that the longer the hydrocarbon chain the more energy will be transferred to the water therefore fewer moles of fuel will be used to achieve the same temperature rise.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work