Chemistry: Developing Fuels
- Created by: Sabriah.ahmed
- Created on: 14-12-13 14:13
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- Developing Fuels
- Petrol
- Diesel
- Diesel has a cetane number of C100
- Petrol
- Petrol has an octane number of C5 - C7
- Octane number is the tendency of a petrol based fuel to auto ignite. the higher the octane number the less likely it is to auto ignite
- Properties
- Flammability - how easily it is ignited
- Knocking: happens if a fuel auto ignites in the engine and also ignited by a spark
- Viscosity - flow from tank to car
- In the winter petrol has to be viscous
- Volatility - needs a balance, has to mix with air but you dont want it to evaporate
- In the summer petrol has to be less volatile so that it doesnt evaporate
- Flammability - how easily it is ignited
- Diesel
- Catalysts
- Cracking
- starts with alkanes that have large molecules that are too big to use in petrol
- larger molecules are broken down to give alkanes with shorter chains that can be used in petrol
- Increases the octane number of petrol
- Zeolite catalyst
- starts with alkanes that have large molecules that are too big to use in petrol
- Isomerisation
- Takes straight chain alkanes and heats them in a catalyst so that the chains break and then let the fragments join together again
- When fragments join up they are more likely to do so as branch
- Aluminium oxide catalalyst
- Seperation of the isomers
- Molecular sieves made from zeolite
- Straight chains pass through the sieve and the branched chains are caught
- Straight chain alkanes are then recycled over the platinum catalyst
- Molecular sieves made from zeolite
- Increase the octane number of petrol
- Reforming
- Straight chain alkanes are converted into ring compounds
- first to cycloalkanes and then to aromatic hydrocarbons
- Increase the octane quality of petrol components
- Cracking
- Enthalpy
- Standard enthalpy change of combustion
- the enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions
- Example: CH4 + 2 02 ? CO2 + 2 H2O
- Standard enthalpy change of formation
- the enthalpy change when one mole of a compound is formed from its elements under standard conditions
- Example: H2O ? H2 _ 0.5 O2
- Standard enthalpy change of reaction
- the enthalpy change when molar quantities of reactants react together under standard conditions
- The enthalpy change gives the quantity of energy transferred to or from the surounding during a chemical change
- Positive enthalpy is ENDOTHERMIC
- Negative enthalpy is EXOTHERMIC
- How to work out the enthalpy: 1) divide joules by 1000 2) Work out moles 3) divide by number of moles
- Breaking bonds requires energy
- Making bonds gives out energy
- Bond enthalpies are not exact they are an average of many compounds
- Standard enthalpy change of combustion
- Entropy
- Alkanes
- Cycloalkanes
- Alkenes
- Straight-chain
- Branched chain
- Alcohols
- Hess cycle
- Hess 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
- Pollutants
- Volume of gases
- Petrol
- The enthalpy change gives the quantity of energy transferred to or from the surounding during a chemical change
- Positive enthalpy is ENDOTHERMIC
- Negative enthalpy is EXOTHERMIC
- How to work out the enthalpy: 1) divide joules by 1000 2) Work out moles 3) divide by number of moles
- Breaking bonds requires energy
- Making bonds gives out energy
- Bond enthalpies are not exact they are an average of many compounds
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