Chemistry Topic 8
Hydrocarbons
Found in crude oil
Only consists of Hydrogen and Carbon
Homologous series
Alkanes
CnH2n+2
Methane
Propane
Ethane
Butane
Pentane
Hexane
A series of compounds which:
Differ by CH2
Have the same general formula
Shows a gradual variation in Physical properties (e.g. boiling points
Have similar chemical properties
Crude oil
Made of a complex of hydrocarbons
Contains useful compounds and are separated using fractional distillation
A finite resource
No longer being made or being made slowly
The molecules in crude oil contain carbon atoms arranged in chains or rings
Gases
Petrol
Kerosene
Diesal oil
Fuel oil
Bitumen
For domestic heating and cooking
Fuel for cars
Fuel for planes
Fuels for trains and cars
Fuel for large ships and power stations
Surfacing for roads and roofs
As you go from bitumen to gases:
The boiling point decreases
The molecule is easier to ignite
The viscosity decreases
It flows easier
Combustion
Complete
Fuel+oxygen->Carbon dioxide+water(+energy)
Only CO2 and H2O
The fuel burns completely
Lots of oxygen
Releases oxygen
Incomplete
Carbon monoxide (toxic gas) and carbon (soot) are also made
Not enough oxygen
The fuel doesn't burn completely
Releases less energy
Carbon
Carbon monoxide
Carbon monoxide binds with haemoglobin in red blood cells which stops oxygen from combining. This spreads around the body
Causes sleepiness, unconsciousness and death
Carbon blocks pipes carrying away waste gases, blackens buildings and causes breathing problems
Acid Rain
Causes
If hydrocarbon fuels that have sulphur in them reacts with oxygen (burns), sulphur dioxide rises and dissolves in rain water which makes sulphuric acid rain.
Makes the soil acidic, killing trees (stops producing oxygen)
Pollutes the sea making it acidic and killing sea creatures
Statues weather because of the acid rain
Quickens the process of corrosion of metals
In engines, it gets hot which causes nitrogen and oxygen to react together which makes oxides of nitrogen (NOx) like nitrogen dioxide (NO2). When it dissolves in rain water, it forms nitric acid (acid rain).
Using hydrogen as a fuel instead of diesel/petrol
Advantages
Disadvantages
Supplier of crude oil for petrol is limited
Diesel and petrol release CO2 causing global warming
Petrol and diesel makes CO(Carbon Monoxide) and carbon.
Hydrogen only produces water as waste
Flammable
Hard to store
Has to be manufactured and is expensive
Energy and electricity is needed to produce
Leaks easily if the fuel system is damaged
Petrol, kerosene and diesel oil are non-renewable fossil fuels obtained from crude oil
Methane is a non-renewable fossil fuel found in natural gas
Cracking
Alkenes
Alkanes
Saturated hydrocarbons (Joined by a single bond)
Unsaturated hydrocarbons (Contains a carbon to carbon double bond)
Splitting a large hydrocarbon into alkenes and alkanes.
A long hydrocarbon is heated and evaporates. The gas passes over the catalyst which causes some covalent bonds to break so it is cracked. An alkane with a shorter carbon chain is formed. The gas is then collected in the test tube.
Breaking strong covalent bonds
Fractional distillation of crude oil
Crude oil put into the column
Heated and vapourises
As you go further up the column, it gets cooler
The compounds in crude oil will cool and condense depending on their boiling points
Longer chains condense at the bottom as it is hotter ans shorter chains condense at the top as it is cooler.
Some hydrocarbons will stay as a liquid
Large hydrocarbons are less useful than small hydrocarbon molecules