enthalpy changes

mass change

=J

So the enthalpy change from burning methanol is J

From my results I can say that the more number of carbon atoms and hydrogen atoms in an alcohol the less fuel needed to burn to produce higher enthalpy changes and that isomers of each other produce slightly different enthalpy changes but I think that this is inaccurate as the same amount of bonds are being broken to burn the alcohol in complete combustion

As more carbon and hydrogen atoms become present in the fuel the enthalpy change increases but not at a constant rate, this data can be plotted on a graph;

In this experiment the percentage errors for each type of reading are as follows;

Thermometer reading, can only be read to the closest half degree so the percentage error for this is 50 divided by the reading

Balance reading as the balance is only two decimal places this can be up to 0.005 either way so the percentage error is 0.5 divided by the reading. The balance was used to measure the weight of the water and also the weight of the fuel before combustion and after combustion.

This graph shows that as the number of carbons and hydrogens increase the so does the enthalpy change. The reason that all the values are negative is because this is an exothermic reaction which means it gives off heat. The reason that the enthalpy change decreases is because more carbon-carbon bonds,carbon-hydrogen bonds are being broken which releases energy, the majority of the energy released is heat energy in this reaction and all the values are for complete combustion which means all the bonds are being broken

Simon Ellis 12 HCF chemistry coursework page 1