The aim of this experiment is to find out how much energy is released when burning different types of alcohol. I am attempting to discover whether the amount of carbon atoms an alcohol contains affects the amount of energy given off through combustion.

Bond Energies

C-H    413 Kj/mol                                    C=O    805 Kj/mol

O=O   498 Kj/mol                                    O-H     464 Kj/mol

Bonds broken                                                                   Bonds formed

C-H x 4                                                                             C=O x 2

O=O x 2                                                                            O-H x 4

Reactants (taken in)                                                         Products (released)

413 x 4 = 1652                                                                 805 x 2 = 1610

498 x 2 = 996                                                                   464 x 4 = 1856

                2648 Kj/mol                                                                      3466 Kj/mol

= 2648 – 3466

= -818 Kj/mol (Exothermic)

We can show this energy change in reactions as a graph of the course of reaction against energy in Kj/mol. Exothermic shows a step down graph, whereas Endothermic shows a step up.

Exothermic Reactions                                                              Endothermic Reactions

To help me predict the outcome of this experiment I am going to work out the bond energies for each of the alcohols. I shall do this using the process featured above in the combustion of Methane in Oxygen reaction.

Methanol              2CH3OH+3O2           2CO2 + 4H2O = 1072 Kj/mol

Ethanol                C2H5OH + 3O2          2CO2 + 3H2O = 1726 Kj/mol

Propanol              2C3H7OH + 9O2          6CO2 + 8H2O = 2347 Kj/mol

Butanol                C4H9OH + 6O2          4CO2 + 5H2O = 2032 Kj/mol

Pentanol              2C5H11OH + 15O2          10CO2 + 12H2O = 2434 Kj/mol

After conducting all of this research, I predict that the stronger the alcohol being burned and the more hydrocarbon atoms it possesses, the more energy it will give off. This is because hydrocarbon atoms are the things that burn, therefore the more of these in an atom’s structure, the more energy it will release during combustion.

Apparatus

To conduct this experiment, I shall use several pieces of apparatus: -

• A Clamp Stand
• 6 Test tubes
• A Measuring Cylinder
• A Thermometer
• 6 Spirit Burners: - 1 Butanol, 1 Pentanol, 1 Propanol, 1 Ethanol and 1         Methanol.

Fair test

To be sure that I am conducting a fair experiment, I am taking several precautions:-

• I shall be very accurate in making sure that I only heat the water for the allocated time of 90 seconds.
• I’ll be extremely accurate when measuring out 20ml of water into my test tube.
• I will make sure that the starting temperature of the water is measured accurately.
• To make sure that no anomalous results are encountered I shall do the experiment twice.

Safety Precautions

I shall be very safety conscious whilst conducting this experiment. I shall: -

• Wear goggles to protect my eyes.
• Use a gauze to protect the desk.
• Utilise a pair of tongues so that I don’t burn my hands when trying to pick up the test tube.

I shall also be very aware of people around me so as to not cause any harm.

Variables

I have decided to test the variables: -

• Amount of water in test tube.
• Distance of test tube from flame.
• Temperature of the water beforehand.

I have selected these three variables as I feel that they will give me the most interesting results.

Diagram

Method

• Firstly, set up the necessary equipment.
• Measure out 20ml of water into the measuring cylinder.
• Transfer the water to the test tube and record the starting temperature.
• Fix the test tube into the clamp stand and position the spirit burner directly underneath.
• Using a splint, light the Spirit Burner and leave to burn for 90 seconds.
• After this time, record the temperature of the water.
• Put the results into table form.
• Pour out the boiling water and leave to cool.

(Repeat this process twice for accuracy)

Results Tables

Results Table for Experiment 1

Results Table for Experiment 2

Conclusion

By analysing my results, I notice that Butanol releases the most energy. This is not what I predicted, as I predicted that the strongest alcohol, in this case Pentanol, would release most energy. I think that this may be caused by Butanol being an anomalous result however, since this happened in both experiments this is unlikely. I feel that the amounts and temperatures I chose were suitable and if I were to perform the experiment again I would use these again. I feel that my results are reliable as I performed the experiment twice. Overall, I feel that my experiment went well and I have learnt a lot.

Evaluation

I am sure that my results are reliable as I conducted the experiment twice and got the same trends in my results both times. I encountered some odd results as Butanol gave off more energy than I expected, however, this occurred in both experiments and so I don’t think that it was a ‘fluke’. If I were to do this experiment again I would possibly take more readings as I feel that this may improve accuracy. Also, I would consider changing the amount of time that I heat up my water as this would provide me with more interesting results.

The fact that my prediction was incorrect shocked me as I had conducted, I feel, plenty of research that helped me to make a prediction. However, I do feel that my experiment went well overall and I think that my results show this.