4.1.2 Alkanes Flashcards
What is an alkane?
A saturated hydrocarbon containing C-H bonds only
What is the general formula of an alkane?
CnH2n+2
Are alkane bonds polar? Why/why not?
Nonpolar because carbon and hydrogen have similar electronegativities
What is the shape and angle of an alkane?
Tetrahedral, 109.5
Describe the sigma bond in an alkane
The sigma bond is a covalent bond which has a direct overlap of the electron clouds of the bonding atoms
What type of intermolecular forces do alkanes have? Why?
London forces because the bonds are non-polar
What happens to the boiling point as alkane chain length increases? Why?
The boiling point increases because there is more surface area and so more london forces, therefore more energy is required to overcome the attraction
Does a branched molecule have lower or higher boiling point compared to equivalent straight chain? Why?
The branched molecule has a lower boiling point because they have fewer surface area and hence less london forces
Are alkanes soluble in water? Why?
Insoluble because hydrogen bonds in water are stronger than alkanes’ london forces of attraction
How reactive are alkanes?
very unreactive
What reactions will alkanes undergo?
Combustion and reaction with halogens
What type of reaction is combustion?
Oxidation reaction
What is complete combustion?
Combustion that occurs with plentiful supply of air
What are the products of complete combustion when alkanes are used?
carbon dioxide and water
What is the colour of the bunsen burner flame during complete combustion?
blue flame
What is incomplete combustion?
Combustion in a limited supply of oxygen
What are the products of incomplete combustion when alkanes are used?
carbon dioxide, water and carbon monoxide
Write an equation for the complete combustion of propane?
C3H8 + 5O2 —-> 3CO2 + 4H2O
What type of hydrocarbons are most likely to undergo incomplete combustion?
longer chains
What is the environmental impact of carbon monoxide?
it is toxic/poisonous
What is the environmental impact of soot (carbon)?
Asthma, cancer, global dimming
How are Haloalkanes formed from alkanes?
By radical substitution
In the presence of what does an alkane react with a halogen?
UV light
What are the 3 stages of free radical substitution?
- Initiation - breaking halogen bond to form free radicals
- Propagation - chain part of the reaction where products are formed but free radicals remain
- Termination - free radicals removed, stable products formed
