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Developing Fuels 27/12/1
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Calculations:
How do you work out 1 mole of a compound?
You add up all the Ar values to give you the Mr E.g H2O = (1x2) +16 = 18
Reacting Masses:
This is when you are asked to figure out the mass of a product…

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Developing Fuels 27/12/1
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Step 1: Calculate the amount of moles using the equation mass(from equation)/ Mr

Step 2: If 1 mole = 24 dm3 then you are able to scale your answer accordingly.

You may also be asked to calculate the mass of a volume of gas
Example:
Calculate…

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Developing Fuels 27/12/1
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Enthalpy
Exothermic:
Exothermic reactions give out energy from the system to the surrounding so the temperature of the
surroundings increases. H is negative because energy has been lost
Endothermic:
An endothermic reaction takes energy into the system from the surrounding so the temperature of
the surroundings…

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Developing Fuels 27/12/1
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If the number of particles increases then entropy usually increases.
Hess Cycles and his law
The enthalpy change for any chemical reaction is independent of the intermediate stages, so long as
the initial and final conditions are the same for each route.
It is useful for…

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Developing Fuels 27/12/1
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Sign is ­ because bonds are made and this is an exothermic process!
Step 4: Write out your equation:


COMMON QUESTIONS:
Why is it that this is so far off the true value?
A bond enthalpy is the average energy needed to break that particular bond…

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Developing Fuels 27/12/1
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Cycloalkanes:
Have the general formula CnH2n
Are saturated
Are not aromatic! ­ They do not have a benzene ring but they aren't aliphatic because they
have a ring structure!

Alkenes:
Have the general formula CnH2n
Are unsaturated
Are aliphatic
Arenes:
Are unsaturated
Are aromatic
For example…

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Developing Fuels 27/12/1
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Straight chain alkanes are heated in the presence of a catalyst so that the chains break and the
fragments join together again but as more branched chains.
It is a reversible reaction so it never goes to completion but instead reaches a state of equilibrium
where…

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Developing Fuels 27/12/1
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Only alternative available is hydrogen all other fuels and methods produce this gas
Nitrogen Oxides NOx
Produced when nitrogen and oxygen from the air react at high temperatures in the engine
Contributes to the formation of photochemical smog which causes breathing problems it also causes
acid…

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Developing Fuels 27/12/1
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Less CO, CxHy, SO2 and particulates than a diesel engine

More NOx emissions than a diesel engine

It is made from waste plants and animal oils and fat so it's renewable but fossil fuels might be used in
the process.

Hydrogen

Water is the only product…

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