Comparing The Enthalpy Changes Of Combustion Of Different Alcohols.

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Ifrah Naz


Comparing The Enthalpy Changes Of Combustion Of

Different Alcohols.



The enthalpy change of combustion of a fuel is a measure of the energy transferred when one mole of fuel burns completely. A value for the enthalpy change can be obtained by using the burning fuel to heat water and using fact that 4.2j of energy are required to raise the temperature of 1g of water by 1oC. In this investigation my aim is to find the enthalpy change of combustion of a number of alcohols so that I can investigate how and why the enthalpy change is affected by the molecular structure of the alcohol.

    I am going to investigate the enthalpy change of combustion for the alcohol homologous series. I will investigate how alcohols with increasing number of carbons affect the enthalpy change when an alcohol goes under combustion. The energy that alcohols release when being used is called the enthalpy change of combustion.

    As I already know that alcohols are a series of organic compounds which all contain a –OH group.

My Prediction:

By using the knowledge that I already have I think that the alcohols with a larger number of carbon atoms within the molecule will have a greater alcohol change of combustion than the alcohols with less carbon atoms. So therefore I predict that as the molecular mass increases so does the enthalpy of combustion.


      The alcohols that I intend to use throughout this investigation are the following 6 alcohols:

  • Methanol - CH3OH solvent; fuel; manufacture of organic chemicals; denaturing ethanol straight chain alcohol.
  • Ethanol - (CH3CH2OH) ethyl alcohol; grain alcohol. A colorless, flammable liquid produced by fermentation of sugars. Straight chains.
  • Butane - CH3CH2CH2CH3, colourless, with a characteristic natural odor
  • Pentan-1-ol –straight chains alcohol.
  • Hexan-1-ol – straight chain alcohol.
  • Propan-1-ol - straight chain alcohol.

Using the alcohols listed above I will measure the amount of energy produced by them when burnt in air. As I am calculating the enthalpy change of combustion, in order to calculate the enthalpy change of combustion for my chosen alcohols.

  • I will firstly burn my chosen alcohol to heat 100cm3 of water
  • Remembering that 4.2 j of energy is needed to increase the temperature by 1g of water by 1oC
  • So therefore I will need to measure the quantity of alcohol that have burned in the experiment and convert it into moles.

All the combustion reactions from the alcohols will be exothermic; exothermic is a process that releases heat, in an exothermic reaction, the enthalpy of the reacting system decreases        is negative. In an endothermic reaction, the enthalpy of the reacting system increases       is positive. The enthalpy change for an exothermic process is negative. Examples of exothermic processes are combustion reactions and neutralisation reactions.

     The graph below shows the enthalpy level diagram for an exothermic reaction, eg burning methane: CH4 + 202           CO2 + 2H20.

To carry out my investigation I will need the following equipment:

  • Draught shield – this is to exclude draught and prevent any energy from being lost.
  • Spirit burner – to burn the alcohols.
  • Thermometer – ranging from 0oC -110oC, to give accurate temperature results
  • 500ml Metal copper Calorimeter – will help to transfer all the energy into the water efficiently.
  • The 6 different alcohols, which are: Methanol, Ethanol, Propan-1-ol, Butan-1-ol, Pentan-1-ol and Hexan-1-ol.
  • Water – 100ml
  • Heatproof mat – to avoid accidents from occurring, e.g. to stop the surface that I am working on from being damaged or burning.
  • Hazard cards – so that I can follow all the safety hazards and be aware of how dangerous or harmful the chemical that I am handling can be for me and others working in the same environment as me.
  • Goggles – to protect my eyes from being harmed by the alcohols.
  • Electronic balance – an electronic balance of 2 decimal places to give me the right degree of accuracy to carry out my investigation precisely.
  • Clamp – to support the calorimeter
  • 100cm3-measuring cylinder – to keep all liquid measurements accurate.
  • Repeat this procedure for all 6 of the alcohols that I am going to use.
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The method that I am going to use to carry out my experiment is:

  • Firstly I am going to measure out 100cm3 cold water, using the measuring cylinder (so that the water I put into the calorimeter is accurately measured out) rather than using an ordinary beaker, as an ordinary beaker is less precise compared with a measuring cylinder.
  • Then I will record the temperature of the water in the calorimeter, using a thermometer to give a good degree of accuracy.
  • After that I will use the clamp to support the calorimeter.
  • Then I ...

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