3.3.2 Alkanes Flashcards
What does it mean by alkanes being saturated hydrocarbons?
each carbon is bonded 4 times with the maximum number of hydrogens possible.
no c=c bonds
How do cycloalkane general formula differ from normal alkanes?
alkanes = CnH2n+2
cycloalkane = CnH2n
Where are alkanes found?
in crude oil
What is Crude oil
mixture of different length hydrocarbons
What is petroleum?
mixture of mainly alkane hydrocarbons that can be separated by fractional distillation
At what temperature is crude oil heated to in order to vaporise?
350 degrees Celsius
Describe the process of fractional distillation of crude oil
- vaporised oil enters the column and rises through trays. LONGEST HYDROCARBONS dont vaporise and run down to the bottom
- the column has a TEMPERATURE GRADIENT (cooler at the top)
- as vapour rises parts of the mixture condense at different temperatures (due to different chain lengths having different boiling points)
- the fractions are drawn off at different levels
- the shortest hydrocarbons dont condense at 20 degrees Celsius so come off as a gas at the top of the column
What is petrol, kerosine, diesel oil, fuel oil, bitumen and gas used for?
p = used in petrol cars
k= jet fuel and heating
f = used in ships and power stations
b = roofing and tarmac
g = LPG and stove gas
define cracking
breaking a longer chain alkane to shorter hydrocarbons
Why do we crack heaver fractions/long hydrocarbons?
heavier fractions e.g fuel oil are in lower demand than lighter fractions such as petrol which are much more valuable
What are the 2 types of cracking?
thermal and catalytic
What are the conditions and products of thermal cracking?
- high temperature of 1000 degrees
- pressure of 70atm
- produces mainly alkenes
What are the uses of products from thermal cracking?
alkenes can be used to make polymers such as plastics. e.g poly(propene)
what are conditions and products of catalytic cracking?
- high temperature of 450 degrees
- slight pressure
- zeolite catalyst
- products are mainly AROMATIC HYDROCARBONS (contain benzene rings) and Motor fuel
What are the products of catalytic cracking useful for?
aromatic hydrocarbons are useful in fuels for vehicles
why is a zeolite needed in catalytic cracking?
using a zeolite catalyst lowers the temp and pressure needed for cracking to happen.
this lowers COST and SPEEDS up the process
Describe the complete combustion of alkanes (reactants and products)
alkanes burn completely in oxygen to form carbon dioxide and water
Why are alkanes good fuels?
most burn readily to produce large amounts of energy
What occurs during incomplete combustion of alkanes?
alkanes burn with limited oxygen supply producing carbon monoxide and or carbon (soot)
Why is carbon monoxide poisonous
it bonds to haemoglobin in the blood and prevents oxygen bonding.
how can carbon monoxide be remove from the back on an engine?
with a catalytic converter
what damage can soot cause?
breathing problems
make buildings dirty
clog engines
What is the greenhouse effect
carbon dioxide absorbs infra red radiation from the sun but emit some back into earth
How does burning fossil fuels lead to global warming?
burning fossil fuels makes carbon dioxide and this is a greenhouse gas.
this increases the greenhouse effect as more infra red radiation (heat) is being emmitted back towards earth causing global temperatures to increase and hence global warming.
