Alkanes Flashcards
What is the general formula of an alkane
CnH2n+2
Name the first four alkanes
Methane, ethane, propane, butane
Describe and explain the process of fractional distillation
Crude oil is heated and fed into a tube
The alkanes are separated via boiling points
So when the vapours reach their boiling points they condense into a liquid and is piped of
Shorter chain alkanes condense nearer to to the top where it is cooler because they have low boiling points
Thick residue collects at base called bitchumen or tar
Why do we crack alkanes
Longer chains alkanes aren’t as useful as shorter chains
Shorter chains can be used as fuels and are more useful
Describe the process of thermal cracking
Produces a high amount of alkenes
Happens at a high temperature (900 degree C and 450 atmosphères)
What are the disadvantages of thermal cracking
It is expensive due to conditions
It is also difficult to determine how short the alkene chain will be
Can be dangerous
Describe catalytic cracking
Takes place under (1 to 2 atmospheres and 450 degree C)
In the presence of a zeolite catalyst
Produces motor fuels
What kind of compounds do catalytic cracking form
It forms aromatic compounds, hydrocarbons, branched alkanes, motor fuels
What does the term saturated mean
Has single bonds only
State the meaning of the term hydrocarbon
Contains only carbon and hydrogen atoms
Why should sulfur compounds be removed from fractions before they are used in central heating
Exam Questions
Sulphur can react with oxygen to make sulphur dioxide which can causes acidic rain
Explain how oxides of nitrogen are formed
the oxygen in the engine reacts with nitrogen in the air under high temperature and pressure
Write an equation to show how nitrogen monoxide in the air is converted into nitrogen dioxide.
2NO + O2 -> 2NO2
Nitric acid (HNO3) contributes to acidity in rainwater.
Deduce an equation to show how nitrogen dioxide reacts with oxygen and water to form nitric acid.
4NO2 + 02 + 2H20 -> 4HNO3
Write an equation for the cracking of one molecule of dodecane into equal amounts of two different molecules each containing the same number of carbon atoms.
State the empirical formula of the straight-chain alkane that is formed.
Name the catalyst used in this reaction.
C12H26 -> C6H12+ C6H14
Empirical formula - C3H7
Catalyst- Zeolite
Name the process used to separate petrol into different fractions
Fractional distillation
What does carbon dioxide contribute to
Global warming
What is the use of a catalytic converter
It is used to remove exhaust gases before they enter the atmosphere
What is the catalyst used in a catalytic converter
Platinum or Rhodium
Write an equation for the incomplete combustion of C8H18 to form carbon monoxide and water only.
A catalytic converter is used to remove carbon monoxide from the exhaust gases in a car. Identify a catalyst used in the catalytic converter.
Write an equation to show how carbon monoxide is removed in a catalytic converter.
(4)
State why the water produced in the exhaust gases may contribute to global warming
Incomplete combustion
C8H18 + 8.5 O2 ~> 8CO + 9H20
Catalyst- Platinum
2CO + 2NO -> 2CO2 + N2
State the reason- water is a greenhouse gas or it absorbs radiation
Why do we use flue gas desulphurisation
To remove waste products
What can unburnt hydrocarbons cause
They can cause respiratory problems
What is the equation to remove sulphur from fuels
Ca0+ SO2 -> CaSO3
How can you use CaSO3
First add some oxygen to make CaSO4
Then you make something called gypsum
Which is used in plastering
Why do nitrogen oxides form
Because of the High temperature and spark from the engine
Name the greenhouse gases
Methane, carbon dioxide, water vapour
Describe the mechanism of global warming
The Earth radiates out infrared long wavelength radiation.
The C=O Bonds in CO2 absorb infrared radiation so the IR radiation does not escape from the atmosphere.
This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed.
Why is a catalytic converter covered in mesh
To increase the surface area
What is wet scrubbing
Involves dissolving calcium carbonate or oxide in water and spraying on acidic sulphur dioxide gas
