Hydrocarbons
Made out of only hydrogen and carbon. |
Alkanes have the general formula HₙC₂ₙ₊₂. |
Alkanes are homologous- they react in a similar way. |
Alkanes are saturated- they all have four covalent bonds. |
The first four alkanes are methane, ethane, propene and butane. |
These can be remembered by My Elephants Pooey Bum. |
As the chains get shorter, the flammability, volatility, and thickness decreases. |
Short chain hydrocarbons are more useful than longer ones. |
Cracking
Cracking is the breaking of long chain hydrocarbons into small ones. |
Cracking produces an alkane and an alkene. |
Cracking is a thermal decomposition reaction. |
Catalytic Cracking- You can pass long chain molecules over a hot powdered aluminium oxide catalyst. |
Thermal Cracking- You can crack hydrocarbons by vaporising them, mixing them with steam and heating them to a very high temperature. |
What ever goes into a cracking reaction comes out. |
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Combustion of Hydrocarbons
The complete combustion of any hydrocarbon in oxygen releases a lot of energy. |
Hydrocarbon + Oxygen --> Carbon Dioxide + Water (+energy) |
Both carbon and hydrogen are oxidised. |
An equation must be balanced. |
Crude Oil
Crude oil is a fossil fuels, formed over millions of years, with high temperatures and pressure. |
It is formed from plankton, and can be drilled up from rocks. |
It is a non-renewable and finite resource. They are being used up much faster than they are being formed. |
Uses of Crude Oil
Oil is used for modern transport. This includes LPG, Heavy Fuel Oil, Diesel Oil and Kerosene. |
All of the products from crude oil are organic compounds. |
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Fractional Distillation of Crude Oil
Crude oil is made out of hydrocarbons, mostly alkanes. |
The oil is heated until most of it turns not a gas. It enters the fractionating column. |
There is a temperature gradient in the column. It is cooler at the top, and hotter at the bottom. |
The shorter hydrocarbons have the lowest boiling points and are condensed at the top. |
You end up with LPG, Petrol, Kerosene, Diesel Oil, Heavy Fuel Oil, and Bitumen. |
Little (shortest chain) Penguins Keep Drinking Hot Beer |
Alkenes
Alkenes have a C=C Double Bond, meaning that alkenes have two fewer hydrogens compare to alkanes. |
Alkenes are unsaturated. |
Alkenes are more reactive than alkanes due to the double bond being able to make a single bond. |
Ethene, Propene, Butene and Pentene. |
The General Formula is: HₙC₂ₙ |
To test for alkenes, you use bromine water, which turns from bright orange to colourless. |
Alkenes can be used to produce polymers and may other chemicals. |
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