• 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

To find a relationship between the molecular size of different alcohols and the associated energy change involved in the reaction.

Extracts from this document...

Introduction

Steven John 11c                

Introduction

The aim of the investigation was to find a relationship between the molecular size of different alcohols and the associated energy change involved in the reaction.

A preliminary experiment had been carried out already and errors were noted accordingly and were adjusted in this experiment where possible.

This investigation looked into the energy changes when different alcohols were combusted, this is the reaction of the alcohol with oxygen in the surrounding air. The alcohols are a homologous series of compounds that contain –OH as the functional group (a group of atoms in a structure that determines the characteristic reactions of a compound). For this experiment, only methanol, ethanol, propanol, butanol and pentanol will be used.

Alcohol

Molecular formula, CnH2n+1OH

Boiling point (ºC)

Methanol

CH3OH

65

Ethanol

C2H5OH

78

Propan-1-ol

C3H7OH

97

Butan-1-ol

C4H9OH

117

Pentan-1-ol

C5H11OH

137

The structures of alcohols

Here’s where the alcohol structures go, sorry I couldn’t send them!

In general,

alcohol + oxygen  carbon dioxide + water

E.g.                 ethanol + oxygen  carbon dioxide + water

                        C2H5OH(l) + 3O2(g) 2CO2(g) +3H2O(l)

Hypothesis

The larger the molecular size, i.e. the more carbon atoms it has, the larger the amount of energy given out.

Some chemical reactions are capable of releasing a lot of energy; usually it is through heat. The combustion of alcohols is a good example, but it is known that they do give off different amounts of heat.

When an alcohol is combusted, it reacts with the oxygen in the air and the products are carbon dioxide and water:

alcohol + oxygen carbon dioxide + water

During this reaction, as with all others, bonds are first broken and then new bonds are made. In alcohol, hydrogen atoms are covalently bonded to hydrogen atoms.

...read more.

Middle

Specific heat capacities: it is understood that different materials are able to store different amounts of energy in a period of time, hence we use the same can throughout the experiment.

Energy released: to allow suitable and accurate comparison between results of the five different alcohols, and to allow an accurate relationship to be produced, we will convert all taken results into a value of total energy released.

Accuracy

To produce results with the maximum accuracy suitable, we repeated the experiment twice in order that we could find an average between the results and hence allowing us to identify and eliminate the anomalous results.

We used the most accurate measuring equipment available, including digital balance to 2 decimal places and a thermometer to the nearest degree.

We also learnt from the causes of errors in the preliminary and adjusted our method accordingly; i.e. the use of draft excludes and taking into accounts the energy stored in the can.

We kept the variable as constant as possible by using the same equipment throughout, based on the concept that different materials have different specific heat capacities and so store different amounts of energy; even if energy is lost we can either account for it or know that it is a constant amount each time, hence still allowing us to make an accurate comparison between results.

We also took all measurements and calculations to 2 decimal places where possible, which we thought to be a suitable accuracy for school laboratory experiments and for finding an accurate relationship. This also was suited to the equipment we chose to use.

Apparatus

Below is a lost op apparatus used in the experiment:

  • Measuring cylinder – to measure out amount of water to be heated 100ml.
  • Fuels (methanol, ethanol, propanol, butanol and pentanol) – used to heat water in can. Stored in spirit burners and weighed with the lid.
  • Beverage can – used to store water, either made of aluminium or steel (allows conduction of heat to the water; has only a small hole to prevent heat loss).
  • Draft excluder – to prevent heat loss from naked flame to environment.
  • Thermometer – to check temperature of the water.
  • Heatproof mat – to conduct experiment upon.
  • Clamp and retort stand – used to hold can above flame.
  • Ruler – used to measure distance between bottom of can and tip of flame.
  • Electronic balance – used to measure mass change of fuel, i.e. amount combusted.
...read more.

Conclusion

The evidence is reliable in showing the sort of trend that would be produced. The anomalous results were also very small and still show the trend clearly and so the results are accurate. The difference in the actual result and the predicted results can also be fully accounted for. The actual results are also more realistic in terms of energy transfer as it takes into account the energy loss. The obtained evidence is sufficient to support a firm conclusion that as the molecular size of the alcohol increases so does the amount of energy released. This is because the results show this trend very clearly and are similar to the predicted results. The anomalies are also not far from the line of best fit and so support the trend making them reliable. Even though the actual results differ from those that were predicted, it can be explained by the fact that energy is lost to the environment.

Further work for this investigation would include testing to see the rate at which energy is produced; how long it takes for each alcohol to heat the water by a certain amount. My prediction would be that the alcohols with the larger molecules would take less time because they have more bonds and so more energy is released in a certain amount of time, and so it would heat the water faster. Additional evidence for the conclusion could also be obtained by continuing the experiment with more alcohols with more carbons and so allowing us to gain a more detailed trend in the relationship. Also by replacing the calorimeter with a thermocouple would allow us to see a more accurate trend and find other factors apart from heat loss that may cause anomalous results.

...read more.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism 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 Electricity and Magnetism essays

  1. Marked by a teacher

    Investigation into Energy Released From Burning Various Alcohols.

    4 star(s)

    539.5 Ethanol 1040.0 Propan-2-ol 1540.5 Butan-1-ol 2041.0 Pentan-1-ol 2541.5 This data was obtained in the following way: * I made a table showing what bonds between atoms, and how many of each, were made. Alcohol Bonds Broken Bonds Made C-H C-O O-H O=O C-C O-H C=O Methanol 3 1 1

  2. To investigate which fuel gives out the most energy when burnt. We are burning ...

    6 X O-H (4 X 460) = 5720KJ/MOL Energy released- 5720 + 4708 = -1012 KJ/MOL Propanol Propanol + oxygen --> carbon dioxide + Water C3H7OH + 41/202 --> 2CO2 + 41/2H20 Bonds Broken 7 X C-H (7 X 410) 1 X C-O (1 X 360)

  1. "My aim is to find out how much energy is released when burning different ...

    With the two temperatures we were able to work out the change in temp. To do this experiment to the next sample we had to change the water and allow the test tube to cool down, and weigh the next crisp.

  2. Measuring the specific heat capacity of water

    I used the formula, which gives 4320 j/kg�C, but then I also used the gradient which in result gave me a more accurate answer of 4235 j/kg�C. As you can see the gradient gives a much more accurate answer, this is because when you use the method of calculating the

  1. Burning Alcohol

    You need more energy to break the bonds of Pentanol than Methanol, so you will get more energy out of burning Pentanol per mole, that you will with burning Methanol per mole. Evaluation My method is good, as it shows a definite trend, as shown in the graph and the conclusion, and they support my original prediction.

  2. Investigating the heat of combustion of a series of Alcohols

    C - O = 16 X 336 = 5376 O - H = 1 X 464 = 464 C - C = 3 X 346 = 1038 O = O = 6 X 497 = 2982 Total Energy in = 8735 kJ Total Energy out = 10016 kJ Energy Released

  1. Finding a material's specific heat capacity

    copper block to help transfer all the heat from the heater to the block and from the block to the temperature probe. This is because oil is much more dense than air and hence, as the particles are more closely packed, is a far better conductor of heat.

  2. To find out what happens to the efficiency of a motor as I change ...

    against efficiency. Newtons Lifted (N) Efficiency 0.10 0.17 0.20 0.21 0.30 0.26 0.40 0.32 0.50 0.33 0.60 0.37 0.70 0.30 0.80 0.43 0.90 0.25 1.00 0.19 ANALYSING AND CONCLUDING Below is a diagram of a running motor. An explanation of what is happening is given below.

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