Combustion of alcohols

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David Downs

Combustion of alcohols

I aim to investigate the heats of combustion in comparison to the number of atoms in the molecule between different alcohols. To do this I will heat some water in a beaker until it has risen in temperature significantly and then will weigh it in order to establish the change in mass thus to work out the heats of combustion. I will use the equation E=MC  T and the specific heat of water (4200j) to calculate the heats. In this equation E is the energy required to raise the waters temperature to the specified heat (j), M is the mass of water in the beaker (kg) and C is the specific heat.    is a Greek letter used in Chemistry to symbolise ‘change in’. Therefore    T is the change in temperature (°c).

 An alcohol is a water molecule with an alkyl group in place of one of the Hydrogen atoms. This is shown here in the example of ethanol:  

Alcohols are told apart by the number of carbon atoms they have. For example Methanol has 1 carbon atom, Ethanol has 2 carbon atoms, Propanol has 3 carbon atoms and Butanol has 4 carbon atoms. The table continues up to Eiconol, which has 20 carbon atoms but we are only concerned with the first 4 as they are the ones I will be using in the experiment.

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Alcohols are written with OH on the end as in       CH OH (Methanol) or C H OH (Ethanol) or C H OH (Propanol) or C H OH (Butanol). The pattern of the carbon atoms creates a formula: C H    with the OH on the end.

Once the energy has been calculated I will use the equation ‘  H =(E/  M)xMr’ to establish the heats of combustion.

Using these principals I would confidently predict that as the number of carbon atoms increases, the heats of combustion will also increase. This is directly due to the ...

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