Free radical Substitution questions
Ex. Methane + Chlorine
1. UV light is required to start this reaction. What does the UV light
do?
2. What is meant by the phrase ‘homolytic fission’? Explain your
answer by putting suitable curly arrows on a Cl-Cl molecule
3. What must always be created in the Propagation steps of a free
radical reaction?
4. Draw two possible propagation steps in the reaction between
methane and chlorine
5. What species are involved in a termination step? Write the
equation for the useful termination step in the reaction between
chlorine and methane
6. What type of reaction is this?
7. The chlorination of ethane in UV light has a free radical
mechanism. The first step is:
Cl2  2Cl
The next step could be either
CH3CH3 + Cl  CH3CH2Cl + H
STEP I
Or
CH3CH3 + Cl  CH3CH2 + HCl
STEP II
Use the bond enthalpy data given below to show which of these two steps,
I or II, is most likely
C-H
C-Cl
H-Cl
Bond enthalpy / kJmol-1
+413
+346
+432