Free radical substitution

Question 1

Is bond breaking endothermic or exothermic?

Answer 1

endothermic

Question 2

Is bond forming endothermic or exothermic?

Answer 2

exothermic

Question 3

What does exothermic mean?

Answer 3

The formation of products give out energy to the surroundings

Question 4

What does endothermic mean?

Answer 4

The formation of products takes in energy from the surroundings

Question 5

What do we call a bond breaking and the electrons being returned to their original atoms?

Answer 5

Homolytic fission

Question 6

What do we call as substance with an unpaired electron?

Answer 6

free radical

Question 7

What energy source is used to cause a halogen bond to undergo homolytic fission?

Answer 7

Ultra Violet (UV) radiation

Question 8

What do we call Group VII elements?

Answer 8

Halogens

Question 9

How many hydrogen halides are made for every halogen substitution into the alkane? ​

Answer 9

Each substituted halogen creates a hydrogen halide.

e.g. C₃H₁₀ + 3Cl₂ → C₃H₇Cl₃ + 3HCl

Question 10

What are the 3 steps in a free radical mechanism called?

Answer 10

1. initiation
2. propagation
3. termination

Question 11

Give an equation for an initiation step in the mechanism using chlorine

Answer 11

UV light breaks Cl₂ down to form chlorine free radicals.​

Cl₂ → 2Cl●​

Question 12

What happens in the first part of the propagation step? Give an equation for methane reacting with Cl● .

Answer 12

The alkane reacts with the halogen radical.​

An H atom is removed from the alkane to produce a hydrogen halide and a hydrocarbon free radical.

Cl● + CH₄ → HCl + ●CH₃​

Question 13

What happens in the second part of the propagation step? Give an equation for methane reacting with Cl● .

Answer 13

The hydrocarbon free radical reacts with the halogen to put a halogen atom onto the hydrocarbon free radical.​

e.g. ●CH₃ + Cl₂ → Cl● + CH₃Cl​

Question 14

Why is the propagation step a chain reaction?

Answer 14

It makes more free radicals which can react again and again.

Question 15

What is a termination step?

Answer 15

Termination is any step that does not produce free radicals.

Question 16

if methane and chlorine react in the presence of UV; what would be a termination step that gave a halogenoalkane?

Answer 16

Cl● + ●CH₃ → CH₃Cl

Question 17

if methane and chlorine react in the presence of UV; what would be a termination step that gave a alkane?

Answer 17

●CH₃ + ●CH₃ → C₂H_6​

Question 18

Why don’t chemists use free radical mechanism to make halogenoalkanes?

Answer 18

It produces a mixture of many products.