Free Radical Substitution

Question 1

Chain reactions

Answer 1

The reaction above is called a free-radical substitution. It starts off a chain reaction which takes place in three stages - initiation, propagation, and termination.

Question 2

Initiation

Answer 2

• The first, step of the reaction is breaking the CI-Cl bond to form two chlorine atoms.
• The chlorine molecule absorbs the energy of a single quantum of ultraviolet (UV) light. The energy of one quantum of UV light is greater than the CI-Cl bond energy, so the bond will break.
• Since both atoms are the same, the Cl—Cl bond breaks homolytically, that is, one electron going to each chlorine atom.
• This results in two separate chlorine atoms, written Clo. They are called free radicals. The dot is used to show the unpaired electron.

Question 3

Why don’t the c-h bands break in an initiation reaction

Answer 3

• The C-H bond in the alkane needs more energy to break than is available in a quantum of ultraviolet radiation, so this bond does not break.

Question 4

Write the free radical reaction for chlorine or bromine

Answer 4

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Question 5

Why are chain reactions so impotent

Answer 5

It is believed that chlorofluorocarbons (CFCs) in the stratosphere are destroying the ozone layer.
Ozone is a molecule made from three oxygen atoms, 03. It decomposes to oxygen..
The ozone layer is important because it protects the Earth from the harmful exposure to ultraviolet (UV) rays. UV radiation causes skin cancer in people by damaging DNA.
Chlorine free radicals are formed from CFCs because the C-Cl bond breaks homolytically in the presence of UV radiation to produce chlorine free radicals,

2023——- 302 is the overall procces