6.24 - Substitution reactions of alkanes Flashcards
What is a substitution reaction?
A reaction where an atom or group is replaced by another atom or group
What is a mechanism?
The sequence of steps in an overall reaction
What does a mechanism try to show?
The changes in bonding throughout a reaction
What happens when chlorine is added to methane, in sunlight?
They react in a substitution reaction
Describe step 1:
- UV radiation breaks down chlorine molecule into chlorine atoms
- This is homolytic fission
- Each chlorine atom is free radical
What is homolytic fission?
When a molecule splits, and each of the bonding electrons leaves with one species, forming a radical
What type of step is step 1?
Initiation step
What is an initiation step?
When one molecule becomes two radicals
Describe step 2:
- Chlorine radicals are very reactive, so when they collide with methane, they remove a hydrogen atom
What is the chemical equation for when the chlorine radical hits the methane?
Cl. + CH4 -> HCl + CH3.
dot should be half way up line
What does the CH3 radical now do?
Reacts with a chlorine molecule
What is the chemical reaction for when the CH3 radical hits a chlorine molecule?
CH3. + Cl2 -> CH3Cl + Cl.
What type of step is step 2?
A propagation step
What is a propagation step?
When a molecule and a radical become a different radical and molecule, and there are two reactions in this step
What 3 reactions take place in step 3?
Cl. + Cl. -> Cl2
Cl. + CH3. -> CH3Cl
CH3. + CH3. -> C2H6
