Investigation into the energy released by burning alcohols

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Investigation into the energy released by burning alcohols


The aim of my experiment is to investigate how much energy is released by 5 different alcohols when they are burnt. These are Methanol, Ethanol, Propanol, Butanol and Pentanol.

Scientific Theory

In the following experiment I will be investigating how much energy is given off when you burn an alcohol. The 5 alcohols I will be investigating are methanol, ethanol, propanol, butanol and pentanol. All of these are part of the homologous series and so they all contain the functional group O-H. Their structures can be shown as follows:

Therefore the general formula for alcohols is:

When each of these fuels is burnt they are all exothermic, combustion reactions. A balanced combustion equation for methanol would be                            CH3OH + 11/2 O2  CO2 + 2H2O. A combustion reaction is when the fuel burns in the oxygen in the air producing carbon dioxide and water. The combustion equation can be used to work out the energy given off by using bond calculations.  The reactions are exothermic because they give off energy to the surroundings and so the energy released that I work out will be a negative number.

The heat energy released can be worked out from an equation. The equation is heat energy = vol of liquid x heat capacity (4.2) x temp change. Once this has been worked out you can find out the kJ/mol released if you have the mass. From the mass burnt you can find the number of moles burnt by doing mass/RMM of the alcohol. When you have the number of moles you divide the kJ released by this number and you get the kJ/mol released.

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The pattern of results that I am looking for is that the longer the chains of alcohols become the more energy is given off. Therefore methanol will give off the least energy and pentanol the most. I think this is what will happen because the longer the chains are the more atoms are made and broken in the full reaction. As the alcohol increases by one carbon atom, in the combustion equation there is 2 extra C-H bonds, one extra C-C bond and 1 and a half extra O=O bonds that are made. These all need energy ...

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