Alkanes

What is the polarity of most alkanes

Non polar

What does the polarity of alkanes mean for their reacitivity

Unreactive

Are alkanes saturate or unsaturated

Saturated

What bonds do alkanes contain

Only single bond

What are alkanes typically derived from

Crude oil

Shape of alkanes

Tetrahedral- 4 bonds around a carbon, 109.5 deg. BA

General formula of cycloalkanes

CnH2n- form a ring

General formula of alkanes

CnH2n+2

Relative MP+BP of straight chain alkanes

High

Why doe straight chain alkanes have a high MP/BP

Have greater contact between linear molecules so has stronger LDF- increases further with length as more electrons= more + stronger LDF

Relative MP/BP of branched hydrocarbons

Low

Why do branched hydrocarbons have a low MP/BP

Less contact between branched molecules so have weaker LDF

Conditions for complete combustion

Excess O2

Example of complete combustion

CH4+ 2O2 → CO2 + 2H2O

Products of complete combustion

CO2 and H2O

Conditions for incomplete combustion

Deficit of oxygen

Example of incomplete combustion of methane

CH4 + 2O2 → 2CO + 2H2O

How is CO2 a pollutant

Increases level of CO2 beyond normal= climate change + global warming

How is CO a pollutant

Binds to haemoglobin so you can’t get enough oxygen

How is C a pollutant

Solid Carbon is soot= global dimming

Radicals

Species with unpaired electrons

Homolytic fission

Where 2 radicals are formed when a bond splits evenly and each atom gets one of the electrons

Heterolytic fission

Where both electrons from a bond go to one of the atoms to form a cation and an anion

What does a curly arrow show

Movement of electron pairs, either breaking or forming a covalent bond

3 steps of free radial substitution

Initiation, propagation, termination

Initiation

The double bond is broken by UV light in reference to others are is requires less energy to separate the atoms

What is a radical shown by

A dot

Initiation step of chlorination of methan

Cl2 → Cl. + Cl.

Propagation step

Free radicals are very reactive as they want to pair up their single electrons so react with a hydrogen form the hydrocarbon

Propagation step of chlorination of methane

Cl. + CH4 → CH3. + HCl

Cl2 + CH3. → CH3CL + Cl.

How can you use the propagation reaction to get the full equation

Remove the free radicals and combine

Full equation of chlorination of methan

Cl2 + CH4 → CH3Cl +HCl

Termination

Occurs when two free radicals meet

Termination reactions of chlorination of methane

Cl. + CH3. → CH3Cl = desired product chloromethan

Cl. + Cl. → Cl2

CH3. + CH3. → C2H6

Why is free radical substitution not very good

Has low yield due to side reactions, unwanted products eg ethan C2H, mixture of products is difficult to seperate