The energy released by an Homologous series of alcohols

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Olivia Blain 11s

The energy released by an Homologous series of alcohols

In this investigation I am going to find out how the amount of energy released is affected by the number of carbon atoms in the alcohol.

The table below shows some information about four member of the alkane family. Alkanes are saturated hydrocarbons.

Reactions of Hydrocarbons

The hydrocarbons called alkanes are fairly unreactive. However, alkanes do burn well to produce energy. Most of the uses of alkanes rely on exothermic reactive when they burn. The combustion of hydrocarbons, including alkanes, requires oxygen from the air. Providing there is a plentiful supply of oxygen, the products are water vapour and carbon dioxide.  If hydrocarbon, including alkanes, burn in a limited supply of oxygen, water vapour is still produced but the poisonous gas carbon monoxide, CO, can be produced.

Measuring Energy released

The following bond energies are in a KJ per mol. One mole of an alcohol contains 6x10-23 molecules.

C-C = 347       C=C = 805

C-H = 413

O-H = 464.

The number and types of bond on the left hand side of:

CH3 OH + 1½O2               CO2  + 2H2O

C-H = 5 x 413 = 2065

C-C = 1 x 347 = 347

C-O = 1 x  358 = 358

O-H = 1 x 464 = 464

O=O= 3 x 498 = 1494  

                                          Total = 4728 KJ

Right hand side:

C=O = 4 x 805 = 3220

O-H = 6 x 464 = 2784


                                    Total = 6004 KJ

Overall energy charge = 6004 – 4728

                                    = 1276 KJ/mole

References: Internet –

                    CD ROM – Encarta

                   Class book – GCSE Chemistry by Bob Mcduell

Preliminary Results


  • Spirit Burner
  • 4 Alcohols (methanol, ethanol, propanol, and butanol).
  • Retort Stand and clamp
  • A large copper container.
  • Thermometer
  • 100 ml of cold water
  • Stop watch
  • Balances
  • Heat resistance mat

  1. First assemble the equipment as in diagram above.
  2. Weigh the filled spirit burner.
  3. Measure out 100 ml of cold water and put it into the copper container, and attach to clamp and stand.
  4. Take the temperature of cold water.
  5. Light the fuel and start stopwatch.
  6. Measure the temperature of the water in the copper container every 30 seconds for 2 minutes.
  7. Put out flame. Measure the burner and record the mass.
  8. Repeat this three times.
  9. Do this for each of the four alcohols.

In the preliminary experiment using various alcohols with a different number of carbons in their molecular structure. I used a simple method, containing heating water using the alcohol, from this I was able to determine the energy released by Ethanol.

The table below show the results of this experiment.

The chemical equation for this exothermic reaction of the Ethanol is:

CH3 OH + 11/2O2                       CO2 + 2H2O

The calculations below shows how I work out the energy released per mole of fuel.

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Number and types of bond for the left hand side of the equation.

C-H = 3 x 413 = 1239

C-O = 1 x 358 =358

O-H = 1 x 464 = 464

O=O = 1.5 x 498 = 747

              Total = 2808 KJ

Number and types of bond for the right hand side of the equation.

C=O = 2 x 805 = 1610

O-H = 4 x 464 =1856

Total = 3466

Overall energy change = 3466-2808


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