chapter 23 reactions in organic chemistry

Question 1

substitution reaction

Answer 1

chemical reaction in which an atom/ group of atoms in a molecule is replaced by another atom/group of atoms

Question 2

mechanism

Answer 2

of a reaction is the detailed step by step description of how the overall reaction occurs

Question 3

why do chemists need the knowledge of the

mechanisms ?

Answer 3

in order to establish the best conditions for a particular reaction , hence maximise the yield of products (eg ; reaction nitrogen + hydrogen = ammonia

Question 4

4 steps of a mechanism

Answer 4

initiation, propagation 1 , propagation 2 , termination

Question 5

(methane + chlorine reaction ) Initiation (step 1 )

Answer 5

UV light provides the energy to split (homolysis) the chlorine bonds into chlorine free radicals

Question 6

homolysis / homolytic fission

Answer 6

a chemical bond dissociation of a neutral molecule generating two free radicals

Question 7

photo chemical reaction

Answer 7

reaction that is brought about by light

Question 8

(methane + chlorine reaction ) Propagation (step 2)

Answer 8

chlorine atom attacks a (m)ethane atom to create hydrogen chloride and a species called (m)ethyl free radical

Question 9

(methane + chlorine reaction ) Propagation (step 3)

Answer 9

(m)ethyl free radical attacks a chlorine molecule to form mono chloro (m)ethane and a chlorine free radical atom

Question 10

chain reaction

Answer 10

reaction that continues on and on because a product from one step of the reaction is a reactant for another step of the reaction

Question 11

(methane + chlorine reaction ) Termination (step 4)

Answer 11

a no. of reactions takes place to stop the chain reaction (form molecules ; chlorine , chloro(m)ethane , ethane/butane

Question 12

chlorination of methane

Answer 12

free radical substitution reaction

Question 13

reaction takes place when exposed to UV light [evidence]

Answer 13

the effect of UV light suggests homolysis (free radical mechanism) of Chlorine molecule to form 2 chlorine free radicals

Question 14

for every photon absorbed thousands of chloro-(m)ethane molecules are formed [evidence]

Answer 14

this suggests a chain reaction is taking place

Question 15

ethane/butane is found in the products

Answer 15

(m)ethyl free radicals must be present , 2 methyl free radicals combine to form ethane / 2 ethyl free radicals combine to form butane

Question 16

adding a source of free radicals (tetra methyl lead) speeds up reaction

Answer 16

only a mechanism involving free radicals would be affected by adding a substance that provides free radicals

Question 17

addition of an inhibitor (oxygen ) slows down the reaction rate

Answer 17

this implies a chain reaction is taking place ( the inhibitor is combining with the free radicals to stop the chain formation

Question 18

uses of fully halogenated alkanes

Answer 18

flame retardants ( discontinued use because of the damage they do to the ozone layer )

Question 19

hydrolysis

Answer 19

the chemical breakdown of a compound due to reaction with water

Question 20

saponification =

Answer 20

base catalyzed hydrolysis of esters

Question 21

saponification formed by

Answer 21

ester + base = acid + alcohol