An investigation into the heat energy released upon burning different fuels

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 Katie Bradley

An investigation into the heat energy released upon burning different fuels

AIM: TO SEE IF THERE IS A RELATIONSHIP BETWEEN THE STRUCTURE OF A FUEL AND THE ENERGY IT RELEASES WHEN BURNT.

A fuel is a chemical, which releases energy when burnt. The reason it releases energy is because the reaction between the fuel and oxygen is exothermic. This means that more energy is released to the surroundings when the bonds in the products are made than is taken from the surroundings to break the bonds in the fuel and oxygen.

In this experiment, the fuel I am using is alcohol. I am using alcohols because they have a wide variety and they give clear results.

There is a large range of alcohols I am going to use in my experiment. Here they are: - METHANOL

                                        ETHANOL

                                        PROPANOL

                                        BUTANOL

                                        PENTANOL and

                                         HEXANOL.

Methanol has only one carbon atom. Ethanol has two carbon atoms.  Propanol, therefore, has three carbon atoms. The list above works in order of both hydrogen and carbon atoms. The number of atoms increases as you go further down the list. In this case, Hexanol has the most hydrogen and carbon atoms making it the most likely fuel to burn faster (making the experiment quick but efficient) and increase the temperature of the water, which I am going to use to measure. Heating the water will produce accurate results in the temperature rise.

I am using the homologous series of alcohols because they have similar structures. Structure is what bonds and atoms a fuel contains. Below are the structures of the fuels I am using: -

METHANOL

ETHANOL

PROPANOL

BUTANOL

PENTANOL

HEXANOL

The homologous series of alcohols have similar structures because they all increase their number of carbon and hydrogen atoms in a pattern. For example, Methanol’s number of carbon atoms is 1, then ethanol’s is increased by another one making its number of carbon atoms 2. This is always increasing by 1. Methanol’s number of hydrogen atoms is 3, making Ethanol’s number of hydrogen atoms 5. This is always increasing from 2 onwards.

All of the alcohols are homologous compounds, which have a special formula to help understand their equations. This is the formula:

Cn H 2n+1 OH

(Number of carbon atoms x number of hydrogen atoms x 2+1, OH)

When I tried out this formula using the propanol and methanol equations, this is what I discovered.

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METHANOL:

PROPANOL:

In order for the energy to be released when the fuel is burnt, the breaking and making of bonds must take place.

        Here is ethanol’s equation which has its bonds broken to produce energy.

Here is the structure of ethanol’s molecules before and after they’ve been broken.

Here is ethanol’s energy level diagram to show how bonds are broken and made to finally produce the net energy out.

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