Alkanes
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What conditions are required for thermal cracking?
• high pressure • high temperature
What is cracking?
the breaking down of longer chain hydrocarbons into shorter chain hydrocarbons
Why is cracking carried out?
• longer chain are not very useful • in a surplus • broken down into smaller, more useful molecules (for which there is a higher demand)
What conditions are required for catalytic cracking?
• slight pressure • high temperature • the presence of a zeolite catalyst
How does the boiling point of shorter chain hydrocarbons compare to that of longer chain hydrocarbons?
they have lower boiling points
Give an equation for the complete combustion of octane
C8H18 + 12.5 O2 –> 8 CO2 + 9 H2O
Give an equation for a reaction that removes nitrogen monoxide in a catalytic converter
2 NO + 2 CO → N2 + 2 CO2
What type of compounds does catalytic cracking produce?
aromatic compounds
What type of compounds does thermal cracking produce?
high proportions of alkenes and alkanes
What are the products of incomplete combustion?
CO and H2O
How does a catalytic converter work?
it uses a rhodium catalyst to convert harmful products into less harmful CO2 and H2O
What are some problems with using carbon-based fuels?
• Incomplete combustion can produce CO which is poisonous. • NOx can be formed in petrol engines, which contribute to photochemical smog and acid rain. • Sulfur-containing impurities in crude oil, results in SO2 forming, which contributes to acid rain. • Carbon particulates can cause cancer and worsen asthma.
Give an equation for the reaction of SO2 that forms H2SO4
SO2(g) + 0.5 O2(g) + H2O(l) –> H2SO4(l)
What is one method for flue gas desulfurisation? Give the equation of this reaction
• A slurry of calcium oxide and water is sprayed into the flue gas • the flue gas reacts with calcium oxide and water to form calcium sulfite • CaO(s) + 2 H2O(l) + SO2 (g) + 0.5 O2 –> CaSO4.2 H2O(s)
What 3 steps are involved in free radical substitution?
Initiation, Propagation and Termination
What is the equation for the initiation step of the chlorination of an alkane?
Cl2 –> 2Cl. UV light needs to be present
What are 2 equations for the propagation step of the chlorination of methane?
Cl. + CH4 –> HCl + .CH3 .CH3 + Cl2 –> CH3Cl + Cl.
What are 3 equations for the termination step of the chlorination of methane?
Cl. + Cl. –> Cl2 .CH3 + .CH3 –> C2H6 Cl. + .CH3 –> CH3Cl
How are oxides of nitrogen formed in engines?
• reaction of nitrogen and oxygen from the air • at high temperatures
What issues do nitrous oxides cause?
• acid rain • respiratory problems
Why are some carbon particulates released from engines?
incomplete combustion