C9 - Crude oil and fuels Flashcards
What is crude oil?
a finite resource that is found in rocks, and is a mixture of a large number of hydrocarbon compounds (mainly alkanes)
How is crude oil made?
it is made from the remains of ancient biomass from marine organisms (mainly plankton) buried under mud over hundreds of millions of years
What is a technical name for the alkanes? What is its definition?
-a homologous series
-a sequence of organic compounds with the same functional group and similar chemical properties
What are the first 4 alkanes?
-methane
-ethane
-propane
-butane
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If asked for a general formula for a homologous series, how should you answer it?
write what is shown below, don’t just put 2n-2
How is crude oil turned into a useful product?
-by fractional distillation, where it is separated into different fractions containing molecules of similar lengths
-each fraction is processed to produce fuels and feedstock for the petrochemical industry
State some examples of materials produced by fractional distillation:
solvents, lubricants, polymers, detergents
State some examples of fuels produced by fractional distillation:
petrol, diesel, kerosene, heavy fuel oil, LPGs
LPG is liquified petroleum gas, not light
Describe the full process of fractional distillation of crude oils:
-crude oil is vaporised (turned into a gas) by heating
-hydrocarbon gases enter fractionating column and rise
-cools down as they get higher
-when the hydrocarbon cools enough to reach their condensing/boiling point, they condense into a liquid
-liquid is collected and separated
Why might nonane condense lower in a fractionating column compared to smaller alkanes?
-nonane has a higher boiling point
-therefore it will condense at a higher temperature, which is found lower in the fractionating column
Describe how 3 factors change with increasing hydrocarbon molecule size:
-boiling point increases
-viscosity (thickness) increases
-flammability decreases
Describe the process of complete combustion with a hydrocarbon fuel:
-exothermic reaction involving the oxidation of the carbon and hydrogen from the hydrocarbon fuel
-complete combustion produces CO₂ and H₂O
Incomplete combustion often forms CO gas or C particulates
How can longer hydrocarbon chains be broken down into smaller ones? Describe this process:
-cracking, 2 methods can be used:
catalytic - high temperature to vaporise HCs and pass over hot catalyst
steam - high temperature to vaporise HCs and mix with steam
What are the products of cracking? Compare their reactive properties:
-alkanes and alkenes
-alkenes are more reactive
How can you test for the presence of an alkene?
alkenes react with bromine water, turns orange to colourless
Give some uses of alkenes:
-polymers
-starting materials for the production of many other chemicals
Why is cracking necessary?
-there is a higher demand for smaller hydrocarbons because they’re usually better fuels as they are easy to ignite
-however most of the fractions have long chains
-cracking takes the longer chains and breaks them down into smaller, more useful chains
They are easy to ignite since they have a higher volatility, making them very flammable
What is the difference between a molecule being saturated and unsaturated? Give an example:
saturated - only single bonds, alkanes
unsaturated - has one or more double/triple bonds, alkenes
Why are sulfur impurities removed from petrol before it is burnt in car engines?
-the sulfur might react with oxygen to form sulfur dioxide (SO₂)
-can dissolve in rainwater to form acid rain
Why is soot sometimes produced when burning fossil fuels?
-incomplete combustion occurs
-due to insufficient oxygen
How would reducing the amount of sulfur in fossil fuels reduce the erosion of limestone?
-less sulfur would react with oxygen in combustion to form sulfur dioxide
-less sulfur dioxide emitted by the car
-less dissolves in precipitation to form acid rain
-limestone reacts less with acid rain
Why are oxides of nitrogen formed in car engines?
-car engines operate at very high temperatures
-this means nitrogen from the air can react with oxygen from the air to form oxides of nitrogen
