Compounds that contain hydrogen and carbon atoms only
Crude oil
A complex mixture of hydrocarbons
Contains molecules with rings or chains of carbon atoms
An important source of useful substances like fuels and feedstocks for the petrochemical industry
A finite resource
Crude oil can be found under the sea and ground
Finite
Will run out
Fractional distillation
1. Crude oil is vaporised before it enters a fractionating column
2. The fractionating column is hotter at the bottom than at the top. The vapours rise up and condense at different fractions depending on their boiling points
3. Hydrocarbons with low boiling points will be tapped off the top of the column and hydrocarbons with high boiling points will be tapped off the bottom of the column
Reason for separating crude oil
Unseparated crude oil isn't very useful but the separated products (such as petrol) are very useful
Uses of refinery gas
Heating and cooking
Fuels used in cars
Petrol (gasoline)
Diesel
Use of kerosene
Aircraft fuel
Use of diesel oil
Fuel for some cars and trains
Use of bitumen
Road surfacing and roofs
Use of fuel oil
Fuel for large ships and in some power stations
Differences between hydrocarbons in each fraction
Boiling points
Ease of ignition
Viscosity
The number of hydrogen and carbon atoms their molecules have
Viscosity
How thick and sticky a substance is
Properties of hydrocarbons tapped from the top of the fractionating column
Low boiling point
Highly volatile
Easily ignited
Shorter carbon chains (small molecules)
Homologous series
Series of compounds which have the same general formula, have similar chemical properties, differ by CH2 in molecular formula form neighbouring molecules, and have slight variation in physical properties
Products from crude oil mostly belong to the alkane homologous series
The only products when a hydrocarbon fuel undergoes complete combustion are water (H2O) and carbon dioxide (CO2)
Energy is given out when a fuel undergoes complete combustion
Complete combustion of ethane
2C2H6 + 7O2 → 4CO2 + 6H2O
Incomplete combustion
Occurs when there is an insufficient supply of oxygen
To ensure complete combustion occurs, the reaction should be carried out with excess oxygen
Products of incomplete combustion
Carbon particulates - soot (C)
Carbon monoxide (CO)
Water (H2O)
Incomplete combustion of methane to form carbon monoxide
2CH4 + 3O2 → 2CO + 4H2O
Incomplete combustion of methane to form carbon particulates
CH4 + O2 → C + 2H2O
Problems with carbon monoxide
Carbon monoxide is a toxic gas
It is colourless and odourless and if breathed in can cause death by preventing the red blood cells from carrying oxygen around the body
Problems with incomplete combustion
Produces carbon monoxide which is toxic and can be fatal if breathed in
Produces carbon particulates (soot) which cause global dimming and respiratory problems
Some hydrocarbon fuels contain sulfur impurities. When the fuel is burned, the sulfur reacts with oxygen to form sulfur dioxide
How acid rain is produced
Sulfur dioxide (produced when combusting impure hydrocarbon fuels) evaporates into the air. It reacts with water in the clouds to form sulfuric acid. This is 'acid rain'
Problems caused by acid rain
Corrodes buildings and statues made of limestone
Kills/damages the vegetation
Lowers the pH of large bodies of water, killing the wildlife
How acid rain is produced
1. Sulfur dioxide (produced when combusting impure hydrocarbon fuels) evaporates into the air
2. It reacts with water in the clouds to form sulfuric acid
3. This is 'acid rain'
Fuel is burned, the sulfur reacts with oxygen to form sulfur dioxide
Problems caused by acid rain
Corrodes buildings and statues made of limestone
Kills/damages the vegetation
Lowers the pH of large bodies of water, killing the wildlife
How oxides of nitrogen are produced from car engines
The high temperature and pressure of a car engine causes nitrogen and oxygen from the air to react together
Problems associated with oxides of nitrogen
Pollutants
Produce acid rain with similar effects as SO2
Cause respiratory problems
Advantages of using hydrogen as a fuel in cars
It releases more energy per kg compared to most other fuels
Water is the only product so no pollutants
Renewable source as hydrogen can be extracted from water
Disadvantages of using hydrogen as a fuel in cars
It is expensive to produce and a lot of energy is required for the electrolysis of water to acquire the hydrogen
Difficult and dangerous to store hydrogen because it is very volatile and easily ignites
Methane
Non-renewable fossil fuel found in natural gas
Petrol, kerosene and diesel are non-renewable fuels
Cracking
Breaking down large hydrocarbons into smaller more useful ones
Saturated alkanes are cracked into shorter chain alkanes and short chain unsaturated alkenes