OZ3: Radical Chain Reactions

Question 1

What is bond fission?

Answer 1

The breaking of bonds

Question 2

What is heterolytic fission?

Answer 2

• Both of the shared electrons in the covalent bond go to just one of the atoms when the bond breaks
• So one atom becomes a negatively charged anion (more electrons than protons) and the other becomes a positively charged cation (more protons than electrons)

Question 3

Where is heterolytic fission common?

Answer 3

In polar bonds with a large difference in electronegativity

Question 4

What is homolytic fission?

Answer 4

• One of the two shared electrons goes to each atom in the covalent bond
• Two electrically uncharged “radicals” are formed

Question 5

What is a radical?

Answer 5

A particle with an unpaired electron

Question 6

Why do radicals have no overall charge?

Answer 6

They have the electronic structure they had before they shared their electrons

Question 7

Why are radicals very reactive?

Answer 7

• Due to their unpaired electron

- Gives them a strong tendency to pair up again with another electron from another substance

Question 8

What does the amount of energy needed to photodissociate depend on?

Answer 8

The bond enthalpy of the bond

Question 9

What is initiation?

Answer 9

• The first step of the radical chain reaction

- Free radicals are produced

Question 10

What is propagation?

Answer 10

• A sequence of reactions
• Free radicals react with molecules to form new radicals
• These new radicals go on to react with more molecules, producing new radicals
• Keeps the reaction going

Question 11

What is termination?

Answer 11

• The final step of the radical chain reaction

- Two radicals react together to form a stable molecule

Question 12

Is termination exothermic or endothermic and why?

Answer 12

Exothermic – energy is released as bonds are formed

Question 13

Give the overall formula for the chlorine and hydrogen radical chain reaction.

Answer 13

H2 + Cl2 ==UV==> 2HCl

Question 14

Give the initiation reaction equation for the chlorine and hydrogen radical chain reaction.

Answer 14

Cl2 + hv ===> Cl. + Cl.

Question 15

How does the Cl2 molecule undergo photodissociation?

Answer 15

Sunlight provides enough energy to break the Cl-Cl bond

Question 16

What type of fission is photodissociation?

Answer 16

Homolytic fission

Question 17

Give the propagation reaction equations for the chlorine and hydrogen radical chain reaction.

Answer 17

• Cl. + H2 ====> HCl + H.

- H. + Cl2 ====> HCl + Cl.

Question 18

Give the termination reaction equations for the chlorine and hydrogen radical chain reaction.

Answer 18

• H. + H. ====> H2
• Cl. + Cl. ====> Cl2
• H. + Cl. ====> HCl

Question 19

Give the overall formula for the methane and chlorine radical chain reaction.

Answer 19

CH4 + Cl2 ==UV==> CH3Cl + HCl

Question 20

Give the initiation reaction equation for the methane and chlorine radical chain reaction.

Answer 20

Cl2 + hv ====> Cl. + Cl.

Question 21

Give the propagation reaction equations for the methane and chlorine radical chain reaction.

Answer 21

• CH4 + Cl. ====> CH3. (methyl radical) + HCl

- CH3. + Cl2 ===> CH3Cl + Cl.

Question 22

Give the termination reaction equations for the methane and chlorine radical chain reaction.

Answer 22

• Cl. + Cl. ====> Cl2
• CH3. + Cl. ====> CH3Cl
• CH3. + CH3. ====> C2H6

Question 23

Give the products of the methane and chlorine radical chain reaction.

Answer 23

• Hydrogen chloride
• Ethane
• Chloromethane

Question 24

Give 2 possible further side products of the methane and chlorine radical chain reaction.

Answer 24

• Dichloromethane

- Trichloromethane

Question 25

Which 2 substances react to form dichloromethane?

Answer 25

Cl2 + CH3Cl

Question 26

Which 2 substances react to form trichloromethane?

Answer 26

CH2Cl2 + Cl.

Question 27

Why is oxygen called a “biradical”?

Answer 27

Two unpaired electrons