C1.4 Crude oil and fuels Flashcards
What is a mixture?
A substance that consists of two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged.
it is possible to separate the substance in a mixture by physical methods including distillation.
What is a hydrocarbon?
A molecule made of hydrogen and carbon atoms only.
What are saturated hydrocarbons called?
alkanes
What is the general formula of alkanes?
CnH2n+2
What are the 1st 4 alkanes?
methane, ethane, propane, butane
What is crude oil?
A mixture of a very large number of compounds
Desccribe how a fractionating column work
it works continuously.
crude oil is pumped in at the bottom
Different compounds within the mixture have different boiling points so vaporise at different temperatures
vaporised oil rises up the column
Vapours condense at different fractions (at their boiling points)
What the properties of short hydrocarbons
lower boiling point- more volatile
less viscous (thick)
more flammable
What does it mean if a hydrocarbon is saturated?
all the atoms have formed bonds with as many other atoms as they can
Describe how the uses of hydrocarbons depend on their properties
more volatility- lower boiling point - ideal as bottled gas
very viscous- covering roads
in a fractionating column, each fraction contains molecules with…
a similar number of carbon atoms
What elements are in most fuels.
carbon and/or hydrogen and may also contain some sulfur
What gases are released into the atmosphere when fuels are burnt?
carbon dioxide, water, carbon monoxide, sulfur dioxide, oxides of nitrogen, particulates
When are oxides of nitrogen formed?
at high temperatures
What do particulates contain?
soot (carbon)
unburnt fuels
What is complete combustion?
When there is plenty of oxygen, all the fuel burns
What is partial combustion?
When there is not enough oxygen, some of the fuel does not burn
When are carbon monoxide and particulates formed?
when there is partial combustion
During combustion, the carbon and hydrogen in the fuels are…
oxidised
What does sulfur dioxide and oxides of nitrogen cause?
acid rain
What des carbon dioxide cause?
global warming
What do particulates cause?
global dimming
What is the impact of acid rain?
- Causes lakes to become acidic- plants and animals may die as a result
- Damages limestone buildings and stone statues
Describe ways to reduce sulfur emissions
sulfur can be removed from fuels before they are burnt. eg- in vehicles.
Sulfur dioxide can be removed from the waste gases after combustion, eg- in powerstations
Describe global dimming
Caused by particulates of soot that are produced when fossil fuels are burnt.
these particles reflect sun light back into space, which reduces the amount of sunlight that reaches earth’s surface.
What are 3 biofuels?
Ethanol, Biodiesel, Hydrogen
What is an advantage of using biofuels?
Carbon neutral and ‘clean’
What are some negatives of using biofuels?
not widely available
ethanol and biodiesel could increase food prices
we can’t make enough to completely replace diesel
expensive to produce
What is ethanol and biodiesel used for?
to run cars
What are alkanes?
hydrocarbons
compounds of hydrogen and carbon atoms only
alkanes are saturated so only have single bonds
General formula is Cn H2n+2
Name the type of reaction that releases energy from a fuel
exothermic
combustion
Explain how petrol is separated from a mixture of hydrocarbons in crude oil
- By the process called fractional distillation
- crude oil is heated to about 350 degrees
- petrol evaporates to form a vapour and it rises up the column
- when petrol cools to its boiling point it condenses
- petrol has a relatively low boiling point and so is collected near the top of the fractionating column
Why do most fuels used in car engines when burnt, the exhaust fumes contain nitrogen oxides?
nitrogen and oxygen in the air react in the hot engine to produce nitrogen oxides
A mixture contains hydrocarbons with different boiling points
suggest a method of separating the mixture
fractional distillation
Where does crude oil come from?
ancient biomass found in rocks
What are biofuels produced from?
plant material
In a fractionating column, the column is ……… at the bottom
hotter
What is a fraction?
an area in a fractionating column where molecules collected have a similar boiling point as they have a similar number of atoms in their chain
Why does burning fuels sometimes produce nitrogen oxides, even though the fuels contain no nitrogen
as at very high temperatures
nitrogen and oxygen in the atmosphere react
