Fuels and Hydrocarbons Flashcards
What is a
hydrocarbon?
a compound containing only carbon and hydrogen
What is
crude oil?
- a complex mixture of hydrocarbons
- containing molecules in which carbon atoms are in chains or rings
- an important source of useful substances
- a finite resource
Describe
fractional distillation.
- crude oil is a mixture of hydrocarbons
- all hydrocarbons are evaporated
- the tower is hotter at the bottom and cooler at the top
- gaseous hydrocarbons enter tower at bottom and travel upwards
- different hydrocarbons have different boiling points
- hydrocarbons with fewer carbon atoms condense later and exit the column further up
- different fractions are separated on the basis of where they condensed
- refinery gases do not condense
- fractions are mixtures of hydrocarbons with similar chain length
What are the uses of
gases
from crude oil?
domestic heating
cooking
What is the use of
petrol
from crude oil?
fuel for cars
What is the use of
kerosene
from crude oil?
fuel for aircraft
What is the use of
diesel oil
from crude oil?
fuel for some cars and trains
What is the use of
fuel oil
from crude oil?
fuel for large ships and in some power stations
What is the use of
bitumen
from crude oil?
surface roads and roofs
What are the trends in physical properties as hydrocarbon chain length increases and decreases?
As the size of the molecule increases, so do the melting and boiling points and the viscosity.
As chain length decreases however, so does volatility and flammability.
What is a homologous series?
A series of compounds which have the same general formula, similar chemical properties, same functional group and trends in physical properties.
What is the formula for the combustion of hydrocarbons?
hydrocarbon + oxygen -> carbon dioxide + water (+energy)
When does incomplete combustion occur?
when there is not enough oxygen
What is
cracking?
the breaking down of long chain alkanes into shorter, more useful, alkanes and alkenes
it is an example of thermal decomposition
Monkeys?
Eat
Penguins
But
Penguins
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What is the general formula for alkanes?
CnH2n+2
Why are alkanes saturated hydrocarbons?
because they contain only (C-C) single bonds
What is the general formula for alkenes?
CnH2n
Why are alkenes unsaturated?
Because they contain (C=C) double bonds
How is bromine water used to distinguish between alkanes and alkenes?
If alkenes are present, the bromine water will be decolourised whereas there will be no change with alkanes.
What is a polymer?
A substance of high average relative molecular mass made up of small repeating units.
What is
polymerisation?
the reaction between many small molecules (monomers) joining up to make a polymer
What are the properties and uses of
poly(ethene)?
‘polythene’
- flexible
- cheap
- can be made into thin films
carrier bags, shampoo bottles, food wrap
What are the properties and uses of
poly(propene)?
‘polypropylene’
- flexible
- strong
- resists shattering
buckets, bowls, crates, ropes, carpets
What are the properties and uses of
poly(chloroethene)?
‘PVC’
- tough
- electrical insulator
- can be made hard or flexible
insulation for electrical wires, windows, gutters, pipes
What are the properties and uses of
poly(tetrafluoroethene)?
‘PFTE’
- slippery
- chemically unreactive
non-stick coatings for pans, containers for laboratory substances
What are the positives and negatives of
recycling
as a plastic ‘solution’?
+the plastic is used again to make new products from old ones
-people have to sort their waste at home before putting it into bins
-it is expensive
What are the positives and negatives of
biodegradable plastic
as a plastic ‘solution’?
+the plastic will be broken down by microbes and removed from the environment
+plastic shopping bags can be made out of this and will be broken down within a couple of months
What are the positives and negatives of
landfill
as a plastic ‘solution’?
+it is the cheapest method of disposing plastics
-it uses lots of land that could be used for growing food
-the plastic will stay in the environment for many hundreds of years without being broken down
What are some general characteristics of
polymers?
- different physical properties to the monomers they came from
- hydrophobic so often waterproof
- durable because they are unreactive
last a long time but break down very slowly
What does catalytic cracking require?
- high temperatures of 600-700°C
- a catalyst of alumina or silica
alumina is aluminium oxide
How is catalytic cracking carried out?
- The alumina or silica catalyst is heated to 600-700°C.
- The alkane is gently heated - causing it to vaporise.
- The alkane vapour passes over the hot catalyst.
- The catalyst allows the reaction to happen much quicker.
- This produces shorter alkanes and alkenes.
- The vapours are collected ‘over water’.
