Alkanes Flashcards
What is crude oil?
⦾ Mixture of different HCs
How can you separate crude oil?
How can this be possible
⦾ Fractional Distillation
⦾ Different lengths of HCs have different bp.s
State the method for separating crude oil?
1 ⦾ Mixture vaporised + fed into fractionating column
2 ⦾ Vapors rise, cool + condense
3 ⦾ Products siphoned off for different uses
How are the short and long HC chains differentiated between?
⦾ Short C chains: lower bp.s - rise higher in column before reaching their bp - collected at top of column
⦾ Long C chains: higher bp.s - don’t rise v. high before reaching their bp. - condense - collect at bottom of column
What are the differences between short and long HC chains?
Short:
⦾ Low bp.
⦾ Reactive (easily ignited)
⦾ Runny
Long:
⦾ High bp.
⦾ ~Unreactive (not easily ignited)
⦾ Viscous
What is the general order in length for long HCs to short HCs?
What are their uses?
LONGEST to SHORTEST: ⦾ Gases - LPG, camping gas ⦾ Petrol (gasoline) - Petrol ⦾ Naphtha - processed to make petrochemicals ⦾ Kerosene (paraffin) - Jet fuel, Central Heating ⦾ Gas oil - Disel, Central Heating ⦾ Mineral oil - Lubricating oil ⦾ Fuel oil - Ships, Power stations ⦾ Wax, Grease - Candles, Lubrication ⦾ Bitumen - Roofing, Road surfacing
Why are long chain molecules cracked?
⦾ Not useful
What are the 2 main types of cracking?
1 ⦾ Thermal
2 ⦾ Catalytic
What is Thermal Cracking?
⦾ Produces alkanes + alkenes
⦾ High temps ~1200K
⦾ High Pa ~700kPa
What is Catalytic Cracking?
⦾ Produces aromatic compounds (with C rings)
⦾ Lower temps ~720K
⦾ Normal Pa
⦾ Zeolite catalyst
What is complete combustion?
Complete the equation for e.g. CH4?
⦾ React with sufficient Oxygen
⦾ Produce Carbon dioxide and Water
⦾ CH4 + 2O2 → CO2 + 2H2O
What is incomplete combustion?
Complete the equation for e.g. CH4?
⦾ React with insuffient Oxygen
⦾ Produce Carbon monoxide and Water (even C)
⦾ 2CH4 + 3O2 → 2CO + 4H2O
Why is Carbon monoxide dangerous?
⦾ Toxic gas
⦾ Odorless
⦾ Colourless
What can remove dangerous gaseous products?
⦾ Catalytic converters
How do catalytic converters work?
⦾ Uses rhodium catalyst
⦾ Convert harmful products into more stable products e.g. CO2 or H2O
What else can incomplete combustion produce?
And why is this dangerous?
⦾ Carbon particulates
⦾ Respiratory problems as they pollute air
Why are Sulfur impurities dangerous in the atomosphere?
⦾ Lead to acidification of water in Earth’s atm
⦾ React to form Sulfuric acid - H2SO4
How can Sulfur impurites be removed from waste products?
⦾ Flue gas desulfurisation
⦾ Use powdered CaCO3 or CaO and gypsum
⦾ Flue gases mix with alkaline slurry + acidic SO2 gas reacts with Ca compounds to form harmless salt
⦾ CaO(s) + SO2(g) → CaSO3(s)
What are Nitrogen Oxides?
⦾ Series of toxic + poisonous molecules
⦾ NOx
How is Nitrogen monoxide produced?
⦾ High Pa
⦾ High temp
⦾ In car engine
⦾ N2 and O2 in air react together
What are the series of Nitrogen oxide reaction that can occur?
⦾ N2(g) + O2(g) → 2NO(g)
⦾ 2NO(g) + O2(g) → 2NO2(g)
Draw out the reaction that occur when catalytic converters remove pollutants?
Start with: C3H8(g)
⦾ C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)
⦾ 2NO(g) → N2(g) + O2(g)
⦾ 2NO(g) + 2CO(g) → N2(g) + 2CO2(g)
What is the Chlorination of Alkanes?
⦾ Alkanes react with Halogen in presence of UV light to produce halogenoalkanes
What is a free radical?
⦾ Particle with an unpaired electron
How do freed radicals form?
⦾ Covalent bond splits equally
⦾ Giving each species 1 electron
Why are free radicals reactive?
⦾ Unpaired electron
What is photochemical reaction?
⦾ Started by UV light
What is a Free Radcial Substitution reaction?
⦾ H atom is substituted by Cl or Br
What are the series of reactions that result for the synthesis of Chloroalkanes?
1 ⦾ Initiation
2 ⦾ Propagation
3 ⦾ Substitutions
4 ⦾ Terminations
Explain Initiation?
⦾ Photodissociation
⦾ Sunlight provides (J) to split Cl-Cl bonds equally
⦾ Each gets 1 e-
⦾ Cl• - highly reactive free radical
Cl2 + (UV) → 2Cl•
Explain Propagation?
⦾ Free radicals used up + made again
⦾ Cl• attacks methane
⦾ New methyl free radical attacks another Cl2
⦾ New Cl• can attack another CH4 until all Cl• or CH4 used up
Cl• + CH4 → •CH3 + HCl
•CH3 + Cl2 → CH3Cl + Cl•
Explain Substitutions?
⦾ If Cl's in excess, H atoms on CH4 eventually replaced by Cl ⦾ You'l get: dichloromethane - CH2Cl2, trichloromethane - CHCl3 tetrachloromethane - CCl4 CH4 + Cl2 → CH3Cl + HCl CH3Cl + Cl2 → CH2Cl2 + HCl CH2Cl + Cl2 → CHCl3 + HCl CHCl3 + Cl3 → CHCl4 + HCl ⦾ But if CH4 in excess, Cl will be used up quickly + products mostly chloromethane
Explain Termination?
⦾ 2 radicals join to end chain reaction + form stable product:
•CH3 + Cl• → CH3Cl
•CH3 + •CH3 → C2H6
Cl• + Cl• → Cl2
