Chemistry- 3.2- Alkanes and Halogenoalkanes

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Chloroalkanes
Alkanes with 1 or more H atoms substituted by a Cl atom.
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Halogenoalkanes
Alkane with at least 1 halogen atom in place of hydrogen. C-halogen bonds are polar, so the delta positive carbon can be attacked by a nucleophile. Halogens react with alkanes in photochemical reactions (reactions started by UV light exposure).
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Free Radical
Particle with unpaired electrons that are formed when a covalent bond splits equally giving 1 electron to each species. Unpaired electron makes them very reactive.
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Synthesis of Chloromethane
Methane+chlorine in UV light. 1.Initiation- free radicals made. Cl-Cl bond splits equally, each atom keeps 1 electron. 2.Propagation- free radicals used up/ created (chain reaction). 2.1- Substitutions. 3. Terminations- free radicals join= stable.
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Chlorofluorocarbons
CFCs- halogenoalkane molecules where all H atoms replaced by Cl or F.
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Ozone Layer (O3)
Absorbs UV. Ozone destroyed by CFCs- Cl' formed when Cl-Cl in CFCs broken by UV- forms ClO'. ClO' reacts with ozone to produce Cl' (chain reaction starts again).
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Nucleophilic Substitution
One functional group substituted for another. Nucleophile attacks polar molecule and replaces a functional group in molecule. Lone pair in nucleophile attacks slightly positive charge on C+creates new bond. C can bond to 4, so nucleophile breaks C-X.
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Elimination Reaction
Molecule loses atoms/ groups of atoms. Occurs because H is slightly positive. OH- acts as base and takes proton from C. C now has spare pair of electrons, so forms C=C. C can only hold 4 bonds, so releases Br. High temp, conc and ethanol solvent.
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Fractional Distillation
Vapourise crude oil at 350C, vapour fed into bottom of column and rises up through trays. Boiling point increase as get bigger due to more VDWs forces in larger molecules. As vapour rises up, it gets cooler, creating temp gradient.
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Cracking
Breaking long chain alkanes into smaller h/c (including alkenes). Breaking C-C bonds. Random.
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Thermal Cracking
High temp, up to 1000C, high pressure. Produces alkenes.
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Catalyst Cracking
Zeolite catalyst (hydrated aluminosilicate), slight pressure and high temp (500C). Produces mostly aromatic h/c (contain substituted benzene rings) and alkanes (motor fuels). + Cheaper (low temp/ pressure) and speeds ror (saves time/ money).
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Incomplete Combustion
Limited oxygen. Produces particulate C, CO and H2O. CO= poisonous, molecules bind to haemoglobin, so O2 can't. Can be removed from exhaust gases by catalytic converters. 2NO+ 2CO--> N2+ CO2. Soot= breathing problems, builds in engine, global dimming.
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Nitrogen Oxides
High temp, pressure and spark in engine cause N2 bonds to break and N2 and O2 react to form toxic NOx., NO can be further reacted to produce NO2. Unburnt h/c react w/ NOx in presence of sunlight to form ground-level ozone- smog, irritates eyes.
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Sulfur Dioxide
Dissolves in moisture in atmosphere and converted into sulfuric acid. Acid rain destroys vegetation, buildings, statues and kills fish. Can be removed from flue gases using powdered CaCO3 or CaO, which reacts w/ H2O and SO2 gas (neutralisation).
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Card 2

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Halogenoalkanes

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Alkane with at least 1 halogen atom in place of hydrogen. C-halogen bonds are polar, so the delta positive carbon can be attacked by a nucleophile. Halogens react with alkanes in photochemical reactions (reactions started by UV light exposure).

Card 3

Front

Free Radical

Back

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Card 4

Front

Synthesis of Chloromethane

Back

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Card 5

Front

Chlorofluorocarbons

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