The Relationship Between The Number of Carbon Atoms In An Alcohol And Its Standard Enthalpy Change Of Combustion.

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Ahzaz Chowdhury 11S4b

Alcohol Chemistry Coursework

The Relationship Between The Number of Carbon Atoms In An Alcohol And Its Standard Enthalpy Change Of Combustion.

INTRODUCTION

Introduction and Aim:

        In this experiment, I am trying to investigate the fact that if there is relationship or common pattern between the amount of carbon atoms in an alcohol and also its standard enthalpy change of combustion.

        When crude oil is heated naphtha is formed, this naphtha includes alkenes. Alkenes are simple forms of alcohol as they are the alcohol that has not yet been mixed with any water, H20. These alkenes come to form a homologous series this series is CnH2n. This means that for every carbon atom there is, there are two times as many hydrogen atoms. When these alkenes are hydrated with water to form an alcohol, another homologous series is formed CnH2n+1OH. This is due to the fact that from water, one hydrogen atom is covalently bonded with the methane and also another hydrogen atom along with an oxygen atom is connected. The basic equation for the formation of an alcohol such as methanol is:

Methene + Water          Methanol

                                             

                                             

                                               CH2     +   H2O                  CH3OH

The above equation is the basis for all of the other alcohols as they are all hydrated in the same way and they also follow the same pattern of the homologous series, CnH2n+1OH.

The alcohols that I am using in this experiment are listed below, together with their formation and also the Relative Molecular Mass:

*Note: It can be seen from above that the increase from

One alcohol to the other is CH2. It can also be seen that

The RMM increases by 14 when the amount of carbons in the alcohol

 increase (1 carbon atoms + 2 hydrogen atoms = 12 + 2). *

All that I have explained above is that of the first part of the aim of this experiment, the amount of carbon atoms in an alcohol. In order to carry out this experiment, I need to know two separate pieces of information, the first is the amount of carbon atoms in the alcohol, this, I have explained above and the second is the harder piece of information to find, this is the enthalpy change of combustion. This piece of information is the difference in the amount of energy required to break bonds within, as this case shows, the alcohol and also to form new bonds.

“The Enthalpy Change of Combustion (ΔH)  = Input Energy – Output Energy”.

Using the above ‘formula’, it can be worked out if the Enthalpy Change of Combustion is an exothermic or an endothermic value. An exothermic reaction would cause a greater energy for the formation of the products than the breaking of the original reactants. An endothermic reaction will be the opposite. With this piece of information, I can firstly work out the true values through the above ‘formula’ but to work out these for my own experiment is a much harder task.

Below, the Enthalpy Change of Combustion is stated and shown for the first alcohol, methanol:

Methanol        +           Oxygen                            Carbon Dioxide     +          Water

 CH3OH         +            11/2 O2                                                                 CO2                         +           2H2O

                       

1   O = O                                                                                                     H ----- O ----- H          

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1/2  O = O                                                                                                     H ----- O ----- H

        1  O = C = O

            H

 |

H ----- C ----- O ----- H

             |

            H

  1. C --- H     ...

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