Investigating which fuel will give out the most energy

Safety

I will be wearing goggles as the investigation uses glassware. If there are any spillages of fuel I will be wiping them up immediately.

Fair Test

For each fuel I will be using a fresh 100ml of water to make sure that the water does not have a high temperature to start with. Another method I will be using to prevent the above occurring is by checking the starting temperature of the water to make sure that it is the same as with the previous fuels. I will also be checking that the beaker is a constant height from the spirit burner to prevent the water getting hotter or colder for the different fuels.

Prediction

We are using the following fuels. Each fuel is listed with its chemical formula.

Methanol – C2H5OH

Ethanol – C3H7OH

Propanol – C3H7OH

Butanol – C4H9OH

Pentanol – C5H11OH

Hexanol – C6H13OH

The fuels with more Hydrogen atoms contain more stored energy. When the fuel is burnt, this energy is released and used to heat up the water. We can calculate the amount of energy released because we know how much energy is stored in each type of bond.

In the table below, – indicates a single bond and = indicates a double bond. A mole is the molecular mass in grams.

By using the balanced formula of the reaction that takes place as the fuel combusts, we can find out how much energy has been released from each fuel.

For example, the balanced equation for the combustion of Propanol is:

2C3H7OH + 9O2 = 6CO2 + 8H2O

2 X (3 X 348 + 7 X 412) + 9 X (498)        ⇒        6 X (348 + 498) + 8 X (926)

        3928 + 4482                                        5076 + 7408

            = 8410                                           = 12484

8410 – 12484 = -4074

So in during the combustion of Propanol, 4074 Kj of energy are released.

Results

In the table, anomalous results are show by a *. The ‘ 4th ’ row is used only if a repeat of the fuel was needed. In the last column of each table I have given the energy released per gram in the fuel.

        This is worked out by using the following equation:

100 x 4.2 x Rise in temperature

Mass of fuel burnt