3: Free Radical Substitution and CFCs Flashcards
Free Radical Substitution Chlorination of Methane CFC's Ozone Formation Uses of Ozone
What is a photochemical reaction?
Reactions that require UV light to start them.
How do free radicals form?
When a covalent bond splits equally to give on electron to each of the atoms.
Why are free radicals so reactive?
Because of their unpaired electron.
What happens in the initiation stage of free radical substitution?
Free radicals are produced when sunlight provides energy to break the Cl2 bond.
Give an equation for the initiation stage of free radical substitution.
Cl2 -> 2Cl*
Give 2 equations for the 1st propagation stage of forming tetrachloromethane.
Cl* + CH4 -> *CH3 + HCl
CH3 + Cl2 -> CH3Cl + Cl
Give 2 equations for the 2nd propagation stage of forming tetrachloromethane.
Cl* + CH3Cl -> *CH2Cl + HCl
CH2Cl + Cl2 -> CH2Cl2 + Cl
Give an equation for the 3rd propagation stage of forming tetrachloromethane
Cl* + CH2Cl2 -> *CHCl2 + HCl
CHCl2 + Cl2 -> CHCl3 + Cl
Give an equation for the 4th propagation stage of forming tetrachloromethane.
Cl* + CHCl3 -> *CCl3 + HCl
CCl3 + Cl2 -> CCl4 + Cl
What happens in the termination stage?
How does this happen?
Two free radicals react to form a stable molecule.
The unpaired electrons on each atom form a covalent bond.
Give 3 possible termination reactions for the synthesis of tetrachloromethane.
CH3 + Cl -> CH3Cl
*CH3 + CH3 -> C2H6
Cl + Cl* -> Cl2
What are CFCs?
Halogenoalkane molecules where all of the hydrogen atoms have been replaced by chlorine and flourine atoms.
What does ozone do?
Ozone absorbs lots if UV radiation from the sun, stopping it from reaching us.
What are the benefits of the ozone layer?
BY absorbing lots of UV light, this reduces the amount reaching our skin, reducing the risk of skin cancer.
Give the initiation reaction for formation of oxygen radicals.
O2 -> O* + O*
