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To Investigate Whether There is a Link Between the Number of Carbon Atoms in Alcohol and its Standard Enthalpy of Combustion

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Introduction

To Investigate Whether There is a Link Between the Number of Carbon Atoms in Alcohol and its Standard Enthalpy of Combustion Contents Introduction Alcohol is the common family name for the hydrocarbon group Alkanols. The generic formula of these organic compounds is: Cn.H(2n+1).OH The first example from the alkanol family is: Methanol - C.H3.OH From the generic formula we can see that different types of alcohols will have different number of carbon atoms. In this project I intend to investigate whether there is a link between the number of carbon atoms in alcohol and its standard enthalpy of combustion ?H. Planning Different members of the alcohol family have different numbers of carbon atoms and should therefore have different enthalpy ?H values. The complete combustion of an alcohol is when it reacts with oxygen in the air to form water and carbon dioxide. In this process energy is required to break the existing chemical bonds (endothermic reaction) and energy is given out by the creation of new chemical bonds (exothermic reaction). If the heat of combustion is a -?H the reaction is exothermic as the products of combustion are at a lower energy level than the reactants. ...read more.

Middle

* Then measure 200 cm3 of water using the measuring cylinder and pour it into the water beaker. * Then a thermometer is used to measure the initial temperature of the water, which should also be recorded. * A lit splint (using the Bunsen burner) is used to light the wick of the alcohol bottle. * The water beaker, containing the water, is to be instantly placed over the burning alcohol on the draught proof tin * Once the temperature of the water reaches approximately 40 degrees Celsius the wick is blown out. * Finally the alcohol bottle is to be removed and re-weighed, and the new mass recorded. Diagram: Safety * Wear safety glasses. * Tie back long hair, tuck in school ties, and button up cuffs. * Ensure there are no naked flames near alcohol being stored or measured. * Clean up any alcohol spills immediately. * Take care not to handle hot apparatus, allow cooling before dismantling and cleaning. * Wear an apron. * If spilt on skin or clothing remove affected clothing to prevent fire risk and wash affected area. ...read more.

Conclusion

This can be used to calculate the theoretical enthalpy of combustion for the alcohols of this investigation. Below is a list showing the theoretical enthalpy of combustion for these alcohols. Methanol = - 659 Ethanol = -1031 Butanol = - 2023 Pentanol = - 2301 Heptanol = - 3511 Octanol = - 4007 As you can see a longer molecule takes more energy to break its bonds, compared to a smaller molecule. However, as the carbon length increases the greater the number of carbon dioxide and water molecules produced as a result of the combustion of the alcohol. This is because the energy released due to the creation of the increasing number of C=O bonds are far greater than the bonds being broken. Hence the net result is exothermic process. Therefore I expect there to be a trend going upwards on my graph. Methanol will have the lowest reading, and as the number of carbons increase in the different alcohols their readings will increase. Therefore I expect the results to be close to my prediction, having considered the theory bond energy. Chemistry Coursework Anil Sood 11G ...read more.

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