Chemistry: Investigation Into How Relative Molecular Mass Affects Its Rate of Reaction

Combustion of Alcohols

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Combustion of Alcohols

THE COMBUSTION OF ALCOHOLS
PROBLEM
Investigate the heat energy in a range of alcohol's used as fuels.
HYPOTHESIS
I predict that octanol will release the most heat energy. This is because there is more bond energy in that molecule than the other alcohols.
Within a molecule there are bond energies that are holding the atoms together. When the fuel combusts a chemical reaction takes place, this breaks the bonds, this requires energy, and makes new bonds this gives out energy. The energy differences between the two tell us how much energy was given out or taken in. We can show this on a graph.
ENERGY CHANGES DURING A REACTION

To find the bond energies in the molecule of the alcohol we have to look at the how much energy is in the separate bonds of the molecule. Below we have a table of bond energies.
Bond Bond Energy (kj/mol)
C - OH 402
C - H 435
C - C 347
H - O 464
C = O 805
If we draw out the structure of each molecule involved in the chemical reaction we can easily find out how much energy is in that molecule.
STRUCTURE OF THE MOLECULES INVOLVED
METHANOL

ETHANOL
PROPANOL
BUTANOL
PENTANOL
HEXANOL
HEPTANOL

OCTANOL
CARBON DIOXIDE

WATER

BALANCED EQUATIONS
If we work in the bond energies into these balanced equations, and we subtract the energy taken in by the breaking of the bonds from the energy given out by the formation of new bonds we will get the total energy released.
METHANOL
2CH3OH + 3O2(r) 2C02 + 4H20
ETHANOL
2C2H5OH + 6O2(r) 4C02 + 6H20
PROPANOL
2C3H5OH + 9O2(r) 6C02 + 8H20
BUTANOL
2C4H7OH + 12O2(r) 8C02 + 10H20
PENTANOL
2C5H9OH + 15O2(r) 10C02 + 12H20
HEXANOL
2C6H11OH + 18O2(r) 12C02 + 14H20
HEPTANOL
2C7H13OH + 21O2(r) 14C02 + 16H20
OCTANOL
2C8H15OH + 24O2(r) 16C02 + 18H20

We can see from the table above Octanol releases the most heat energy. This clearly shows that there is a correlation between the number of bonds in the molecules and how much total energy was released.
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