# Investigating the alcohols that use the most amount of energy to burn.

Investigating the alcohols that use the most amount of energy to burn

Aim

To find out which fuel uses the most amount of energy per mole

Background Information

We know already how atoms can ‘exchange partners’ in chemical reactions. This means that the bonds which join atoms to each other must be broken. However, new bonds have to be made as the product forms.

Energy is needed to break bonds, it is like pulling 2 strong magnets apart, to pull the 2 magnets apart you require energy, therefore ‘breaking bonds’ requires energy and because it requires energy this means that it is endothermic. When you make new bonds it is the opposite of the above, it is like 2 magnets moving together because of the attraction, and because making bonds gives out energy it is exothermic.

Bond Energy

Bond energy is the amount of energy needed to break chemical bonds. We are able to calculate this energy from the table below, were we can see that particular bond require more energy than others to break. We can see from this table that bond energy is written in KJ/mol. ∆H is also measured in KJ/mol. This unit stands for Kilojoules per mole and it is the energy needed to break a set number of bonds. (A number which a chemist calls a ‘mole’).

The chemical equations for the first four alcohols are:

Methanol – CH3OH

Ethanol – C2H5OH

Butanol – C4H9OH

Propanol – C3H2OH

Heat of Combustion

The alcohols that we will use form together to make a homologous series. The first four in the series are

When we burn the alcohols, they form carbon dioxide and water releasing energy.

The heat of combustion is defined as the heat released when 1 mole of the substance is completely burnt in oxygen. You can calculate the energy absorbed by the water using:

E=mcθ

Where m= the mass of the water, θ= the temperate rise and c= the specific heat capacity of the water).

Preliminary Results

Now that we have found the amount of mass lost for each alcohol we are able to calculate the energy produced in amount of energy per gram and the amount of energy per mole.

Methanol

Methanol energy produced                = mass of water * 4.2 * θ

= 20 * 4.2 * 12

= 1008J

So amount of energy per gram         = energy produced (J) / mass lost (g)

=1008 / 1.5

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