Reactions (and mechanisms)

Question 1

Complete combustion

Answer 1

alkane+O2 -> CO2 + H2O

Question 2

Incomplete combustion

Answer 2

alkane+O2-> CO + H2O

alkane+O2-> C+ CO +H2O

Question 3

Catalytic cracking

Answer 3

zeolite catalyst + 450oC

hydrocarbon-> shorter chain alkane+alkenes

Question 4

Isomerisation

Answer 4

alkane->branched alkane

Question 5

Reforming

Answer 5

Alkane->cyclic alkane+H2

Question 6

Free radical substitution

Answer 6

Initiation reaction

(homolytic fission of halogen using UV)

Br2-> 2Br

Propagation reaction

(radical halogen and alkane)

(radical alkane and diatomic halogen)

Br + CH4 -> HBr + CH3

CH3 + Br2 -> CH3Br + Br

Termination steps

(Two radicals)

Br+Br->Br2

Br+CH3->CH3Br

CH3+CH3>C2H6

Question 7

Hydrogenation

Answer 7

alkene+ hydrogen -> alkane

(Ni catalyst 150’C)

catalytic hydrogenation produces margarine by reacting polyunsaturated vegetable oils with hydrogen and a nickel catalyst

Question 8

Halogenation

Answer 8

alkene+halogens-> dihalogenoalkane

alkene+hydrogen halide -> halogenoalkane

Can make isomers

Question 9

Hydration

Answer 9

alkene+steam->alcohol

(acid catalyst e.g. H3PO4 300’C 6MPa)

hydration makes ethanol from ethene

When unsymmetrical alkenes react with a H20 you can make isomers

Question 10

Elecrophilic addition

Answer 10

When a (halogen) approaches the alkene, a temporary induced dipole is formed, giving the halogen a slightly negative and slightly electropositive end.

Curly arrow starts at the pi-bond (C=C) and points to electropositive end of halogen.

Second curly arrow shows movement of bonded pair of electrons in the halogen bond to the slightly electronegative end resulting in heterolytic fission of this bond.

An intermediate carbocation and a negative halide ion are formed.

The third curly arrow is from the :X- lone pair of halide to the + carbocation.

Question 11

Addition polymerisation

Answer 11

Addition polymerisation of alkenes

one alkene molecule (monomer) joins to others and a long-chain molecule (polymer) is formed.

Question 12

Combustion of alcohols

Answer 12

C2H5OH+3O2->2CO2+3H2O

Question 13

Esterification

Answer 13

Alcohols with carboxylic acids in the presence of an acid catalyst

Question 14

Dehydration

Answer 14

Elimination of H2O from alcohols in presence of an acid catalyst and heat (forms alkene and water)

Can use cyclic hydrocarbons

Can form isomer (double bond in different place depending on H lost)

Question 15

Fermentation

Answer 15

Fermentation from sugars ie from glucose

anaerobic fermentation involving yeast

C6H12O6(aq)->2CH3CH2OH(aq)+2CO2(g)

Question 16

Oxidation of primary alcohols, secondary and tertiary alcohols

Answer 16

Cr2O72-/H+ (ie K2Cr2O7/H2SO4)

Each oxidation reaction is accompanied by a colour change from orange to green.

Use [O] to represent the oxidising agent.

the oxidation of primary alcohols form aldehydes when distilled and carboxylic acids when refluxed (and water produced)

the oxidation of secondary alcohols form ketones (and water produced)

the resistance to oxidation of tertiary alcohols

Question 17

Hydrolysis

Answer 17

The hydrolysis of halogenoalkanes is a (nucleophilic) substitution reaction.

When a primary halogenoalkane is heated under reflux with a hot aqueous solution of an alkali (NaOH or KOH, water solvent), its oxidised to a primary alcohol.

CH3CH2Br+NaOH->CH3CH2OH+NaBr

Question 18

Rate of hydrolysis

Answer 18

Aqueous silver nitrate in ethanol can be used to compare these rates, H2O can be assumed to be the nucleophile. Ag++X-—>AgX(s)

Alternatively, hot aqueous alkali can be used, followed by the neutralisation and addition of aqueous silver nitrate. In this reaction, OH- is the nucleophile.

Question 19

The Haber process

Answer 19

N2+3H2->2NH3

iron catalyst

Question 20

ozone maintenance

Answer 20

O3+(UV)->O2+O

O2+O->O3 (+heat)

O2+O ⇌?O3

Question 21

Ozone break down

Answer 21

R+O3->RO+O2

RO + O->R + O2

Question 22

Catalytic converter

Answer 22

4CO+2NO2->4CO2+N2

Adsorption of CO and NO to the catalyst surface (must be weak enough for adsorption and desorption but strong enough to weaken bonds and allow reaction)

Chemical reaction

Desorption of CO2 and N2 from the catalyst surface