Topic 10
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What are the two types of bond fission?
Heterolytic and homolytic
What is homolytic bond fission?
• A covalent bond between two atoms breaks and each atom takes an electron • formation of free radicals
What is heterolytic bond fission?
When a covalent bond is broken between two atoms in a molecule with one taking both electrons
What is produced in complete combustion reactions?
CO2+H20
Why do alkanes make good fuels?
Release large amounts of heat
What are the products of incomplete combustion?
C or CO
Why are alkenes reactive?
They have a carbon carbon double bond
What reaction do alkenes undergo?
Electrophillic addition
Hydrogenation
Alkene+ H2= Alkane Reagant= Ni Conditions = high temperature and pressure
Halogenation ( with halogen)
Alkene+ Haolgen= Dihaloalkane C2H4+Br2=CH2BrCH2Br
Halogenation ( with hydrogen halides)
Alkene+ Hydrogen halide = halogenoalkanes Reagant= The hydrogen halide C2H4+HBr= CH3CH2Br OR CH2BrCH3
Hydration
Alkene+ H20 = Alcohol Reagant = H2SO4 Conditions = H20 as steam
What do unsymmetrical alkenes have?
More than one end product
Oxidation of primary alcohols
-Partial oxidation = aldehyde ( CHO) Condition = heat under distillation Reagant= Acidified potassium dichromate Colour change = Orange - Green -Further oxidation = carboxylic acid( COOH) Condition= Heat under reflux Reagant= Acidified potassium dichromate Colour change = Orange - Green
Oxidation of secondary alcohols
Complete oxidation = ketones ( C-CO-C) Reagant= Acidified potassium dichromate Colour change = Orange - Green Condition = Heat under reflux
Oxidation of tertiary alcohols
-NONE
What reaction does halogenoalkanes undergo?
• Nucleophilic substitution - SN1 and SN2
What are nucleophiles?
Have lone pairs of electrons to donate and are attracted to regions of positive charge
What reaction do alkanes undergo?
Free radical substitution and as they have low reactivity
Why are alkanes unreactive?
• carbon to carbon single bond • the C and H bonds are non polar • The C-C and C-H bonds are relatively strong
Free radical substitution for methane and Cl
-Alkanes + haolgen = Dihaloalkane or halogenoalkane Initiation Cl2 -- Cl. + Cl. Propagation CH4+Cl. = CH3. + HCl CH3.+ Cl2 = CH3Cl+ Cl. Termination Cl.+Cl.= Cl2 CH3.+CH3. = C2H6 CH3.+ Cl. = CH3Cl
What is the test for unsaturation?
• When bromine water is added to an alkene and the water is decolourised because there is a double bond • When added to an alkane there is no colour change • Unsaturated = double bond or triple bond • Saturated = single bond
What is PVC?
A polymer made from chloroethene
How are additional polymers formed?
When smaller unsaturated molecules react together