alkanes and alkenes

why do alkenes undergo electrophilic addition reactions

• double bond in alkenes is an area with high electron density

• this attracts electrophiles allowing the alkene to undergo an addition reaction

stereoisomerism

• molecules with the same structural and molecular formula but different arrangement of atoms in space

when does E-Z isomerism arise

• when there is restricted rotation around the C=C double bond

• there are two different groups attached to the carbon in the C=C double bond

electrophile

• electron pair acceptor

why is the industrial hydration of alkenes a preferred method of making alcohols

• no waste products - high atom economy

• separation of products is easier and cheaper to carry out

poly(chloroethene)

• waterproof polymer

• electrical insulator

• does not react with acids

PVC

• poly(chloroethene) when plasticiser added

• weakens intermolecular forces allowing the chains to move more easily

• more flexibility in polymer

• in this form it is used to make insulation on electrical wires and waterproof clothing

explain why there is an attraction between a C=C double bond Br2 [3 marks]

• C=C double bond is an area of high electron density

• Br-Br becomes polarised

• δ⁺ Br attracted to C=C

what is fractional distillation used for

• separating liquids with similar boiling points

cracking

• conversion of large hydrocarbons to smaller hydrocarbons molecules by breakage of C-C bonds

• chemical process involving the splitting of strong covalent bonds

economic reasons for cracking

• petroleum fractions with shorter C chains are in more demand than larger fractions

• products of cracking are more valuable than starting materials

thermal cracking

• 700 kPa

• 400 - 900°C

• produces mostly alkenes and sometimes produces hydrogen

reforming

• process of forming branched and cyclic alkanes from straight chain hydrocarbons

catalytic cracking

• slight or moderate pressure

• 450°C

• zeolite catalyst

• produces branched and cyclic alkanes and aromatic hydrocarbons

• used to make motor fuels

how can SO2 be removed

• can be removed from waste gases from furnaces by flue gas desulfurisation

• basic calcium oxide reacts with the acidic sulfur dioxide in a neutralisation reaction

• SO2 + CaO → CaSO3

use of calcium sulfite

• can be turned into calcium sulfate

• this can be used for plasterboards

name the pollutants and their environmental consequences

• NO

  • toxic

  • can form NO2 gas which is toxic and acidic and forms acid rain

• CO

  • toxic

• CO2

  • contributes to global warming

• unburnt hydrocarbons

  • contributes towards formation of smog

• soot

  • global dimming and respiratory problems

catalytic converters

• remove CO, NOx and unburned hydrocarbons from exhaust gases

• 2CO + 2NO → 2CO2 + N2

• C8H18 + 25NO → 8CO2 + 12.5N2 + 9H2O

name the greenhouse gases

• CO2

• methane

• water vapour

why do alkanes not react with many reagents

• C-C and C-H bonds are relatively strong