4.1.2 - Alkanes Flashcards
What shape of alkanes
Tetrahedral
109.5
What happens as the alkane chain increases.
- Boiling and melting point increase.
- This is because the bigger the molecule or atom the more induced dipole-dipole forces as you have larger electron clouds
- So more energy is required to break them
What does branching do to the boiling point
Decrease boiling point
- less surface points of contact
- less compact
- weaker induced dipole-dipole forces
What does complete combustion produce
Carbon dioxide (CO2) and water (H2O)
What does incomplete combustion produce ?
Carbon monoxide (CO)
- Carbon -soot as well
What are the problems with the products of incomplete combustion
Carbon monoxide is toxic.
- Its colourless and odour less
what is cracking ?
conversion of large hydrocarbons to smaller molecules of by breakage of C-C bonds
Why do we need catalytic cracking ?
- To produce more useful hydrocarbons.
Conditions for thermal cracking
- High temps 450-900 degrees celsius
- 70 atm
Conditions for catalytic cracking
- high temp 450 degrees temp
- 1 - 2 atm
- zeolite catalyst
- Turns straight chain alkanes into
branched and cyclic alkanes and
Aromatic hydrocarbons
What condition does free radical substitution take place in ?
In the presence of UV light
What is a free radica
A reactive species which
possess an unpaired electron
What does UV light do ?
Causes the Single covalent bond to break.
Free radical sub between methane and bromine
free radical substitution between chlorine and methane
last product would be
Cl*+ Cl *-> Cl2
- Excess Cl2 present will promote further substitution and could produce CH2Cl2
, CHCl3 and CCl
