Ozone: Radical Reactions

Question 1

When are radicals formed

Answer 1

When molecules absorb at higher energies and bonding electrons separate

= homolytic fission = covalent bonds break and radicals formed

Question 2

Definition of homolytic fission

Answer 2

Electrons shared equally when bond is broken

Leads to radical formation

Question 3

Definition of heterolytic fission

Answer 3

shared electrons go to one atom when bond is broken , forms ions

Eg. In polar molecules

Question 4

What does heterolytic fission involve

Answer 4

Covalent bonds breaking to form ions

Question 5

What are the 3 main steps in radical reactions

Answer 5

1. Initiation
2. Propagation
3. Termination

Question 6

What happens in initiation

Answer 6

Initial reaction forming radicals by action of light energy ( hv )

Eg. Cl2 ——> 2Cl •

Question 7

What happens in propagation

Answer 7

Reactions produce new radicals that keep the reaction going

eg. Cl• +H2 —> HCl + H•
H• + Cl2 —> HCl + Cl•

Question 8

What happens in termination

Answer 8

Reactions terminate radicals and remove them

1. Cl• + H• —> HCl
2. Cl• + Cl• —> Cl2
3. H• + H• —> H2

Question 9

What kind of mechanism is propagation also know as

Answer 9

Radical substitution

Question 10

How is ozone produced in the atmosphere

Answer 10

• In stratosphere dioxygen atoms PHOTODISOCIATE ( hv on arrow ) to form oxygen atoms
  1. O2 —> O + O
• resulting oxygen atoms collide with O2 / O / O3 in following ways
  2. O + O2 —> O3 = ozone
  3. O + O —> O2
  4. O + O3 —> 2 O2 ( termination )

Question 11

What happens when ozone absorbs absorbs radiation in the 10.1 x10^14 - 14.0 x10^14 Hz ( hv )

And what is the reaction responsible for

Answer 11

• molecules undergo photodissociation ( hv on arrow )

O3 —> O2 + O

• reaction is responsible for ozone acting as a screening effect