Enthalpy Changes of Combustion of Different Alcohols

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Recommended: Investigation on combustion of alcohols

Comparing the Enthalpy Changes of Combustion of Different Alcohols

Aim

Combustion of alcohols is exothermic; energy is given out. Salter's

Chemical storylines says, " Different fuels have different enthalpy

changes". I will investigate how the carbon chain length of the

alcohol affects its enthalpy of combustion.

Preliminary Work

----------------

Chemistry for you page 184 says, "breaking bonds requires energy, it

is endothermic ". It also says " making new bonds gives out energy it

is exothermic". The difference between the two determines whether the

reaction is exothermic or endothermic. It also determines how much the

total enthalpy of combustion is this can be shown in energy level

diagrams.

Diagram 1 is an energy level diagram of an exothermic reaction. It

shows that more energy is given out making bonds than is used breaking

them. Combustion is an exothermic reaction.

Diagram 2 is an energy level diagram of an endothermic reaction. It

shows that more energy is used breaking bonds than is used to make

them.

Number and Range

I plan to use five alcohols in this experiment. The alcohols I will

use are; methanol, ethanol, propanol, butanol and octanol.

It is important that I use five alcohols so that there are enough

results to spot any patterns. The experiments are to be done three

times so that an average can be taken this will make the results more

reliable because any anomalous results will have less affect on the

overall findings.

The first four of the alcohols listed above have carbon chains with

1,2,3 and 4

Carbons. I chose to use these alcohols with an increasing number of

carbon atoms in their carbon chains. The reason for this is I can

investigate whether the change in the enthalpy of combustion increases

by the same amount for every extra carbon in the carbon chain. I also

decided to use octanol it has

a carbon chain length of eight so it has twice as many carbons as

butanol. So I can see if the enthalpy of combustion is proportional to

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