SC20 Fuels Flashcards
Define hydrocarbon
A compound that contains hydrogen and carbon only
What is crude oil?
- complex mixture of hydrocarbons of different sizes
- thick, sticky black liquid that is found in porous rock
What is crude oil used for?
- fuel for vehicles such as aircraft, ship, heating and power stations
- feedstock or raw materials for the petrochemical industry
Define petrochemicals
Substances made from crude oil, such as poly(ethene) and other polymers
Define finite resource
Resources that are not made anymore (or are being made extremely slowly) which limits the amount available to us
Why is crude oil a finite resource?
It is being used up faster than it is being produced
Why is crude oil important fror the petrochemical industry?
- The fuels that are used in most modern methods of transport are all based on oil products
- these are all product obtained from crude oil
Define non renewable
Fuels that are being used up faster than they can be formed
How is crude oil formed?
- ancient remains of microscopic animals and plants that once lived in the sea
- became covered in layers of sediments
- the high temperatures and pressure caused the sediments to turn into rocks, therefore trapping the gas and the oil
How do we separate crude oil into different hydrocarbon?
Using fractional distillation
Describe how crude oil is separated by fractional distillation
- crude oil enters fractionating column, so vapours rise
- vapours with very high boiling points will immediately condense, into liquids lower down and are tapped off
- vapours of hydrocarbons with low boiling points will rise up and condense at the top of the column
What are the different compounds obtained from crude oil?
- natural gas
- petrol
- kerosene
- diesel oil
- fuel oil
- bitumen
Define fractional distillation
The separation of a liquid mixture into fractions differing in boiling point by means of distillation, typically using a fractionating column
What determines what fraction a molecule will go into?
The size and length of the hydrocarbon
Explain how the fractional distillation of crude oil works
The different hydrocarbons in crude oil have different boiling points, due to the differing chain lengths. This allows the hydrocarbons to be grouped into fractions of a similar boiling point, allowing for the separation of them
What is natural gas used for?
Domestic heating and cooking
What is petrol used for?
Fuels for cars
What is kerosene used for?
Jet fuel
What is diesel used for?
Fuel for some cars and trains
What is fuel oil used for?
Ships and power stations
What is bitumen used for?
Surfacing roads and roofs
What is common in each fraction
- similar properties
- similar boiling points
- similar chain lengths of hydrocarbons
Define viscosity
Refers to the ease of the flow of a liquid
Why does the boiling point increase as the chain length increases?
As the molecules get larger, the intermolecular forces of attraction between the molecules becomes greater as there is more surface area in contact between them. This means more heat is required to separate the molecules, leading to an increase in boiling point
Why does the viscosity increase with chain length?
Due to intermolecular forces of attraction increasing as the molecular size increases
Why does the ease of ignition decrease as the chain length increases?
As the molecule size increases, they become harder to ignite as more energy is needed to do so, and therefore the smaller molecules are more flammable
Explain why the properties of different fractions differ
Due to the chain length
Describe the main features of a homologous series
- same general formula
- difference between one molecular formula and the next is CH2
- graduation in their physical properties
- same functional group
- similar chemical group
Why do alkanes form a homologous series?
They have the same general formula and the same functional group, which also means that they differ by CH2 each time
Describe the complete combustion of a hydrocarbon
Reaction in which:
- only carbon dioxide and water are produced
- energy is given out
When does incomplete combustion occur?
When there is a limited supply of oxygen
What happens during the incomplete combustion of a hydrocarbon?
- water is produced
- energy is given out
- carbon monoxide and soot are produced
State the names of some fossil fuels
- coal
- oil
- natural gas
What is the main hydrocarbon found in crude oil?
Alkanes
Why is carbon monoxide a toxic gas?
- it combines with the haemoglobin in red blood cells
- which prevents oxygen from combining
- this reduces the amount of oxygen carried in the bloodstream
- causing suffocation and even death
What gases are released through the burning of fossil fuels?
- carbon monoxide
- oxides of nitrogen
- carbon dioxide
- sulfur dioxide
What causes acid rain?
Sulfur and nitrogen oxides
Describe the effects of acid rain
- causes corrosion to metal structures, buildings and stattues made of carbonate rocks
- crops do not grow if soil is too acidic
- excess acidity in rivers and lakes prevents fish eggs from hatching, and it can kill fish and insects
How is sulfur dioxide formed?
- part of hydrocarbon fuels as impurities, such as petrol and diesel
- release when burnt
How does sulfur dioxide cause acid rain?
- sulfur dioxide formed from combustion dissolves in rainwater droplets to form sulfuric acid
- which then falls with rainwater
How are oxides of nitrogen produced?
Formed when nitrogen and oxygen react at high temperatures in internal combustion engines and blast furnaces
How do oxides of nitrogen cause acid rain?
- Nitrogen dioxide reacts with rain water to form a mixture of nitrous and nitric acids
- which contribute to acid rain
- when droplets containing these acids are heavy enough, they will fall as acid rain
What are installed in cars to prevent the formation of nitrogen oxides?
Catalytic convertors
What is an alternative fuel we can use instead of petrol and diesel?
Hydrogen fuel
What are the advantages of using hydrogen fuel?
- releases more energy per kg as compared to other fuels
- does not pollute as it only produces water on combustion, no other product is formed
What are the disadvantages of using hydrogen fuel?
- expensive and requires energy for the production process
- difficult and dangerous to store as it is stored in highly pressurised containers
Define cracking
Involves breaking covalent bonds in hydrocarbon molecules
What are the two types of cracking?
Catalytic cracking and thermal cracking
How is cataylitic cracking carried out?
- crude oil fractions are heated to evaporate them
- vapours are passed over a catalyst containing aluminium oxides
- this breaks the covalent bonds when they come into contact with the surface of the catalyst, causing thermal decomposition reactions
- this produces a random selection of alkanes and alkenes
How is steam/thermal cracking carried out?
- process carried out similar to catalytic cracking, but at higher temperatures
- vapourised hydrocarbons are mixed with steam and heated to a high temperature, which induces cracking
Why is cracking necessary?
The demand for certain fractions of crude oil is higher than its supply, so therefore we must convert the surplus unwanted fractions into more useful ones to supply the demand
Is cracking an endothermic or exothermic reaction?
Endothermic
What are the two hydrocarbons formed by cracking?
An alkane and an alkene
What is the difference between a saturated and an unsaturated bond?
- saturated: single bonds between the carbon atoms eg: alkanes
- unsaturated: form double bonds between the carbon atoms
