# OCR Salters Developing Fuels Revision

Includes all the theory and storylines information you need to know. Examples and calculations that you actually have to do yourself. Stuff about pollution, cracking, reforming things like that.

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• Created by: Laura
• Created on: 25-02-11 23:15

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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 formed or reactant used up.
Example:
What mass of magnesium oxide is produced when 1.2g of magnesium reacts with carbon dioxide?
Mg = 24.3 and O = 6.0
Step 1: Write out a balanced equation and underline the substances involved.
Step 2: under each substance write the amount of moles that is given.
Step 3: Calculate the masses of each substance
Step 4: You divide the substance whose mass you are given in the equation by itself so it equals 1g
in this situation it's the reactant. You then divide the other substance by the other mass and multiply
by the mass given in the equation.
Volumes of gases:
Important to remember that 1 mole of any gas at room temperature is always 24dm3
Really similar to reacting masses except the will ask for the volume of a gas instead
Example:
What volume of Carbon Dioxide is produced when 2.0g of Calcium Carbonate is heated?
Step 1: Write out a balanced equation:
Step 2: Write out the moles involved in the reaction
Step 3: Write out the masses and volumes involved (Mr of product and 24dm3 for gas)
Step 4: Divide the substance that is not a gas by itself to give 1 and then divide the gas by that substance
mass and multiply by the mass given in the equation
Sometimes you will get a different question involving gases where you are asked to calculate how
much volume is occupied by a certain mass of a gas.
Example:
Calculate the volume occupied by 4.4g of carbon dioxide at room temperature and pressure

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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 the mass of 1.…read more

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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 decreases. H is positive because energy has been gained.…read more

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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 calculation unknown enthalpy changes when data has been given!
Example:
Bond Enthalpies
Bond enthalpy is the average energy required to break the bonds in 1 mole of gaseous compounds.…read more

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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 as is not specific to the
molecule in an equation
Bond enthalpies are for gaseous molecules and this may not be the molecules standard state.…read more

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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 ethylbenzene
Auto Ignition & Octane Numbers:
Auto Ignition is the explosion of a fuel without a spark
Octane Numbers ­ are a measure of the tendency of petrol to auto ignite!

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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 no further change can take place.…read more

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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 rain
Reduced by catalytic converters
Sulfur Oxides SOx
Sulfur in the petrol reacts with the oxygen in the air in the heat of the engine
Causes acid rain
Low sulphur petrol can be produced as…read more

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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 of combustion
Highly flammable
High pressure fuel tanks are needed to store it as a liquid.…read more