Fuels Flashcards
Crude oil
A fossil fuel formed over millions of years from ancient remains of marine organisms
Hydrocarbons
Compounds that contain carbon and hydrogen atoms only
Finite resources
- Are no longer being made
- Or are being made extremely slowly
Fractional distillation
Used to separate crude oil into simpler more useful mixtures
During fractional distillation:
- Oil is heated to evaporate it
- Vapours rise in a fractionating column
- The column has a temperate gradient (hot at the bottom, cool at the top)
- Each fraction condenses where it becomes cool enough and is piped out of the column
Properties of fractions
Number of C and H atoms decreases up the column
Boiling point decreases up the column
Ease of ignition increases up the column
Viscosity decreases up the column
Alkanes
A homologous series of compounds
Uses of fractions
Gas- domestic cooking Petrol-fuel for cars Kerosene- fuel for aircraft Diesel- fuel for some cars and trains Fuel oil- fuel for large ships and some power stations Bitumen- surfacing roads and roofs
Features of a homologous series
- Molecular formulae of neighboring members differ by CH2
- Show a gradual variation in physical properties (e.g boiling points)
- Have similar chemical properties
Chemical properties of alkanes
Alkanes undergo complete combustion. When they react completely with oxygen, carbon dioxide and water vapour form
General formula of an alkane
CnH2n+2
Incomplete combustion
Incomplete combustion happens when the supply of oxygen to a burning fuel is limited
Incomplete combustion in vehicles
Faulty gas boilers can produce carbon monoxide and soot
Carbon monoxide
Attaches to hemoglobin in red blood cells, preventing oxygen attaching instead. This reduces the amount of oxygen carried around the body by the bloodstream.
Two problems caused by soot
- Soot can build up in chimneys where it may eventually cause fires
- Blackens buildings
Acid rain
Rainwater is naturally acidic, but acid rain is more acidic than normal
Sulfur dioxide
Hydrocarbon fuels may contain impurities such as sulphur compounds. When the fuel burns, the sulfur in these impurities is oxidizes to form sulfur dioxide.
This dissolves in the water in clouds to form a mixture of acids including sulfurous acid
Sulfurous acid is oxidized by oxygen in the air to form sulfuric acid
The effects of acid rain
- Acid rain increases the rate of weathering of buildings made of limestone or marble
- Acid rain increases the rate of corrosion of metals, such as the iron in steel, weakening them
Oxides of nitrogen
In car engines, fuel is mixed with air and ignited inside the engine. This causes temperatures high enough for nitrogen and oxygen in the air inside the engine to react together. These reactions produce various oxides of nitrogen (NOx)
These are atmospheric pollutants
Nitrogen dioxide and acid rain
Nitrogen dioxide forms dilute nitric acid when it dissolves in the water in clouds
Cracking
Cracking involves breaking covalent bonds in hydrocarbon molecules.
- Crude oil fractions are heated to evaporate them
- The vapors are passed over a catalyst containing aluminum oxide and heated to 650c
- This speeds up reactions that break down larger hydrocarbon molecules
- Smaller more useful molecules form and these can be used as fuels or for making polymers
