Presentation on theme: "Alkanes From Crude Oil (a mixture of Hydrocarbons) Cracking"— Presentation transcript:
1 Alkanes From Crude Oil (a mixture of Hydrocarbons) Cracking Pass Alkane overHEATED Al2O3 catalystFractional DistillationAlkanesUsesNon Renewable sourceReactivityNo Reaction with acid or alkalisNo Reaction with Br2?
2 Fractional Distillation Separation by Boiling PointEach fraction has a different number of Carbons (C1-C4) (C5-C7) (C8-C10)…(C30-C40)What varies as the molecule size changes?Home
3 UsesFuelsWhat 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 BurnerHow 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 CombustionEase 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 temperatureStronger VDWHOME
7 Isomerisation and Reforming Weakens VDW so more vapour Better ignition Straight to BranchedStraight to cyclic
8 Practical 2 Reactions of alkanes Observations of Bromine reaction Br2 decolourised AND an acidic gas producedReaction only occurs when UV light is present
13 Further propagation steps and termination steps two propagation stepsCH3Cl + ClCH2Cl + HClCH2Cl + Cl2CH2Cl2 + Cltermination stepCH2Cl + ClCH2Cl2CH CH3CH3CH3termination step
14 CrackingIs 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)HOME