1. Alkanes From Crude Oil (a mixture of Hydrocarbons) Cracking
Pass Alkane over
HEATED Al2O3 catalyst
Fractional Distillation
Alkanes
Uses
Non Renewable source
Reactivity
No Reaction with acid or alkalis
No Reaction with Br2?

2. Fractional Distillation
Separation by Boiling Point
Each fraction has a different number of Carbons (C1-C4) (C5-C7) (C8-C10)…(C30-C40)
What varies as the molecule size changes?
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3. Uses
Fuels
What do we do when we use them as fuels?
Feedstock for alkenes

4. Practical One Place a small amount of Hexane (C6H14) Octane (C8H18)
Paraffin (C20H42)
Onto a heat proof mat in turn and ignite with a Bunsen Burner
How easy to they ignite?
How sooty is the flame?
What products are formed in a good supply of Oxygen?
What products are formed in a poor supply of Oxygen?
Why do the flames get more sooty?

5. Combustion
Ease of combustion decreases as more C in alkane Flame gets more sooty as more C in alkane CO2 and H2O formed ONLY if oxygen supply is good CO and C (soot) formed if poor air supply (Called INCOMPLETE combustion) As alkanes have more C in molecule more moles of O2 per mole of alkane are required for complete combustion WRITE EQUATIONS

6. Ease of combustion Vapour Burns
Less Vapour as molecule increases in size at same temperature
Stronger VDW
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7. Isomerisation and Reforming Weakens VDW so more vapour Better ignition
Straight to Branched
Straight to cyclic

8. Practical 2 Reactions of alkanes Observations of Bromine reaction
Br2 decolourised AND an acidic gas produced
Reaction only occurs when UV light is present

9. Bond Breakage
X-X  X. + X.
X-X  X+ + X-

10. Free radical substitution
chlorination of methane
i.e. homolytic breaking of covalent bonds
Overall reaction equation
CH4 + Cl2
CH3Cl + HCl
Conditions
ultra violet light
excess methane
to reduce further substitution

11. Free radical substitution mechanism
ultra-violet
Cl2
Cl Cl
initiation step
two propagation steps
CH4 + Cl
CH3 + HCl
CH3 + Cl2
CH3Cl + Cl
termination step
CH Cl
CH3Cl
CH CH3
CH3CH3
minor termination step
Already leads to multiple products

12. Further free radical substitutions
Overall reaction equations
CH3Cl + Cl2
CH2Cl2 + HCl
CH2Cl2 + Cl2
CHCl3 + HCl
CHCl3 + Cl2
CCl4 + HCl
Conditions
ultra-violet light
excess chlorine

13. Further propagation steps and termination steps
two propagation steps
CH3Cl + Cl
CH2Cl + HCl
CH2Cl + Cl2
CH2Cl2 + Cl
termination step
CH2Cl + Cl
CH2Cl2
CH CH3
CH3CH3
termination step

14. Cracking
Is the product a bigger or smaller molecule than the paraffin?
Is the product more or less flammable than the paraffin?
What happens when Br2 is added to the product?
Smaller as it is a gas (so weaker VDW so lower bp)
More flammable (as it is a gas already)
Br2 decolourised without UV light (it is an alkene)
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