crude oil and fuels

• a hydrocarbon is any compound that is formed of hydrogen and carbon atoms only
• crude oil is a fossil fuel formed by the remains of dead plants and animals - mainly plankton , over millions of years the high temperature and pressure the remains turn to crude oil which can be drilled up from the rocks where it is found
• crude oil is a mixture of lots of different hydrocarbons
• a homologous group is a group of organic compounds that react in a similar way
• the structure of an alkane is a chain of carbon atoms with hydrogen atoms bonded to them
• the general formula for an alkane is CnH2n+2
• the first four alkanes are methane, ethane, propane and butane
• Crude oil can be separated using fractional distillation, where the oil is heated until most of it has turned into gas, these gases enter a fractionating column, while the liquids are drained off.
• In the fractionating column, there is a temperature gradient from hot at the bottom to cooler as you go up.
• The longer hydrocarbons have higher boiling points and condense back into liquids and drain out of the column early on when they are near the bottom.
• The shorter hydrocarbons have a lower boiling point and condense and drain out much later on near the top of the column where it is cooler.
• The crude oil mixture is separated out into different fractions which each contain a mixture of hydrocarbons with the same amount of carbon atoms, so have similar boiling points.
• The different length hydrocarbons are used for different things.
• a 40 carbon hydrocarbon would be used for heavy fuel oil
• a 20 carbon hydrocarbon would be used for diesel oil
• a 15 carbon hydrocarbon would be used for kerosene
• an 8 carbon hydrocarbon would be used for petrol
• a 3 carbon hydrocarbon would become liquified petroleum gas ( LPG)
• the shorter a carbon chain the more runny the hydrocarbon is - less viscous
• hydrocarbons with shorter carbon chains are more volatile - they have lower boiling points
• the shorter the carbon chain the more flammable the hydrocarbon is
• when burning fossil fuels, CO2 is released into the atmosphere
• the symbol equation for complete combustion of methane: CH4 + 2O2 > CO2 + 2H2O
• in combustion both carbon and hydrogen are oxidised and carbon dioxide is produced
• the two waste products from complete combustion are water vapour and carbon dioxide
• complete combustion takes place where there is sufficient supply of oxygen whereas incomplete takes place when there is an insufficient supply of oxygen
• During a complete combustion reaction the hydrocarbon fuel burns with a blue flame while during an incomplete combustion reaction the hydrocarbon fuels burns with a yellow sooty flame.
• hydrocarbons are cracked because the short chain hydrocarbons are flammable so make good fuels which are in high demand
• the products of cracking are alkanes and alkenes
• cracking is a thermal decomposition reaction
• a thermal decomposition reaction is a reaction that brakes molecules down by heating them
• catalytic cracking: heat long chain hydrocarbons to vaporise them, pass the vapour over hot powdered aluminium oxide catalyst, the long chain molecules split apart in the surface speck of catalyst
• steam cracking is where you vaporise hydrocarbons and mix them with steam , then heat them to a high temperature
• balanced cracking equation: decane > octane + ethene
• alkenes are hydrocarbons which have a double bond between two of the carbon atoms in their chain
• alkenes are used for polymers, lubricants, and fuels
• alkenes burn with a smokey flame
• alkenes are more reactive then alkanes because the double bond can open up to make a single bond allowing the two carbon atoms to bond with other atoms
• when orange bromine water is added to an alkene the water will become colourless as the bromine will add across the double bond