# Burning Fuels Coursework

10/10/06

Chemistry Coursework

In my chemistry coursework I will be investigating the amount of thermal energy different fuels will provide when burnt. My project brief is to “Examine alternative fuels for a power station that has until recently burnt coal. The fuel that gives the best value for money ratio will be the next one used in the power station.”

The costs of the fuels are:

Fuel                                                Cost in £ per kg.

Methanol                                        5.10

Ethanol                                                7.20

Propan-1-ol                                        7.10

Butan-1-ol                                        6.20

Pentan-1-ol                                        16.90

Bond Energy Calculations

The bond energy of a molecule is the energy released after it has reached the ‘barrier’ – the input energy needed for the bonds to break. Different bonds release different amounts of energy. The bond energy of all the fuels listed above needs to be calculated so that I can work out how much heat energy each fuel should theoretically produce when burnt, and then apply it to a formula to work out how cost effective that particular fuel is.

Working out KJ/£

Methanol

16.81 KJ/g

£5.10 per kg

=0.00510 per gram

16.81

0.00510

= 3,296.08 KJ/£

Ethanol

22.51 KJ/g

£7.20 per kg

=0.00720 per gram

22.51

0.00720

= 3,126.39 KJ/£

Propan-1-ol

25.57 KJ/g

£7.10 per kg

=0.00710 per gram

25.57

0.00710

= 3601.41 KJ/£

Butan-1-ol

27.10 KJ/g

£6.20 per kg

=0.00620 per gram

27.10

0.00620

= 4,370.97 KJ/£

From my KJ/£ equations the fuel that I predict would provide most value for money is ‘Butan-1-ol.’ This is because of its relatively low price when compared to the other fuels. Buntanol is the fourth largest molecule - and as such it provides more energy (27.10 KJ/g) and at the lowest price (£6.10) than any of the others specified.

To measure the energy expelled by each of the fuels, the following formula was used:

Mass x Specific Heat Capacity X Temperature Rise = Heat Energy Gained

(kg)             (J/KgoC)                      (oC)                        (J)

Specific heat capacity is the measure of the  required to raise the  of a specific quantity of a substance by one Kelvin. A  is a unit increment of  and is equal to an increment of one degree .

Energy is a difficult variable to measure, and it can never be taken as 100% accurate, as there will be some form of energy loss in any activity. To measure the exothermic energy supplied by burning each of the fuels above, a container of water will be placed close to the flame of the fuel. A temperature change will be measured and then the fuel will be weighed to find how much fuel has been used to produce the change in water temperature. The least amount of fuel used to produce the same temperature change will be the most effective energy transferring fuel – this will be compared to the price to work out how cost effective it is.

The material the container is made out of will central to my preliminary work, as a more conductive material will raise the temperature of the water to a higher degree than a less conductive object. Other control variables are: The height of the fuel wick, the length between the wick and the beaker, whether the container will have a lid on and any insulation (if required.)

Apparatus

Container (Copper, Aluminium, Coated Black Aluminium)

Clamp

Heat Resistant Mat

Methanol Fuel

Water

Thermometer

Lid for Container.

...

#### Here's what a star student thought of this essay

The authorÃ¢â‚¬â„¢s spelling and grammar is very good throughout, and they have presented their report well with clear sections with sensible headings. They have made good use of tables and graphs to display their results, and used very good scientific vocabulary throughout. However, at times they donÃ¢â‚¬â„¢t appear to quite understand this, for example they said Ã¢â‚¬Å“To measure the exothermic energy supplied by burning each of the fuels aboveÃ¢â‚¬Â when they were measuring the thermal energy released by the combustion of each fuel. However, for the most part they have shown a very good knowledge of chemistry and how to present their work well.

The author began their investigation by using bond enthalpy values to predict the cost per KJ of energy released by burning each fuel. Although they have not quite appeared to understand the definition of bond enthalpies, saying Ã¢â‚¬Å“The bond energy of a molecule is the energy released after it has reached the Ã¢â‚¬ËœbarrierÃ¢â‚¬â„¢ Ã¢â‚¬â€œ the input energy needed for the bonds to breakÃ¢â‚¬Â, when a better definition would have been the energy required to break a particular bond in a gaseous molecule. It is also unclear where these values came from, as they do not match the values for the enthalpy of combustion in my data booklet. I would have quoted the enthalpy of combustion values from the data booklet, then converted these from KJ/mol to KJ/kg, and finally calculated the cost per KJ of energy produced (or the number of KJ per pound). This just makes it much clearer to the examiner how you got the values, as well as showing some mathematical ability. After predicting which fuel would be best, the author carried out the experiment. They did similar calculations to calculate how cost effective each fuel was, and compared their results to the predicted results, calculating the percentage yield. Although they have identified some anomalies in their data, I would have shown how I calculated that these were anomalies, using: anomalies > mean + 0.5 x interquartile range or < mean Ã¢â‚¬â€œ interquartile range. This just tells the examiner exactly what you are doing so he can give you more marks for it! Occasionally, the author doesnÃ¢â‚¬â„¢t explain things very clearly, for example I would have explained the purpose of the preliminary experiment at the beginning of that section, rather than at the end, which makes the report much easier to follow. They have also occasionally said things such as Ã¢â‚¬Å“the prediction that pentan-1-ol would require the least fuel to heat the waterÃ¢â‚¬Â without explaining where this came from, which could easily confuse the reader.

The author has successfully carried out an experiment to choose a fuel for a power station which would be the most cost-effective. They have calculated the percentage yield of each of the fuels, and used bond enthalpy values to predict the best fuel, and used this information alongside their experiment to come to a well reasoned conclusion, and considered sources of uncertainties in their experiment, as well as suggesting improvements.