Ozone: Haloalkanes

Question 1

How do homogenous catalysts work

Answer 1

By forming intermediate with with a lower activation energy

Question 2

What is the 1st step of destruction of ozone by chlorine and bromine

Answer 2

In stratosphere chloromethane (CH3 Cl) and bromomethane (CH3 Br) are broken up by solar radiation (hv on arrow ) into chlorine and bromine atoms

Eg. Inititiaton = CH3 Cl —> Cl• + CH3

Question 3

What are the next steps in destruction of ozone by chlorine and bromine after chlorine and bromine atoms are formed ( though initiation)

Show using equations

Answer 3

1. Cl• +O3 —> ClO• + O2
2. ClO• + O —> Cl• +O2

Overall equation ( combine 2 equations and cancel like terms )

= O3 + O —> O2 + O2

Question 4

What 2 reactions compete to remove O3 ( ozone )

Answer 4

1. O3 + O —> O2 + O2

2. Cl• +O3 —> ClO• + O2

Question 5

In the stratosphere what is there a high concentration of. Cl or O atoms

Answer 5

High concentration of O atoms than Cl

Question 6

Given that concentration of Cl in stratosphere is much less than O atoms. Which removes ozone more

Answer 6

Cl atoms because this reaction:

Cl• +O3 —> ClO• + O2

Is 1500x faster than this reaction:

O3 + O —> O2+ O2

Question 7

What is the concentration and speed of catalytic cycle of bromine compared to chlorine in the stratosphere

Answer 7

Bromine = 100x faster then chlorine but the concentration of bromine is very low in the stratosphere

Question 8

What are the general catalytic cycle equations

Show using radical X

Answer 8

1. X + O3 —> XO + O2
2. XO + O —> X + O2

Overall equation:

3. O + O3 —> O2 +O2

Question 9

Definition of hydroxyl radicals

Answer 9

Radicals formed by oxygen atoms resting with water in stratosphere

Question 10

Give equations for hydroxyl radicals catalytic cycle

Answer 10

1. HO• + O3 —> HO2• + O2
2. HO2• + O —> HO•+ O2

Overall equation:

3. O + O3 —> O2 +O2

Question 11

What does nitrogen monoxide, NO reacting with ozone form

Answer 11

1. Nitrogen dioxide, NO2

2. Dinitrogen, N2O

Question 12

How is nitrogen monoxide catalytic cycle completed

Answer 12

NO2 reacting with oxygen to form nitrogen monoxide, NO and dinitrogen, N2O

Question 13

What are NO and NO2 considered as

Answer 13

Radicals which are relatively stable

Question 14

Cloroalkanes do not deplete in the troposphere in the same way as in the stratosphere resulting in harmful tropospheric ozone

explain the statement and discuss the impact this has on the environment ( 5 )

Answer 14

1. fewer Cl atoms formed in troposphere than in stratosphere
2. Radiation of high enough frequency is too low in troposphere
3. Ozone depletion can only occur in troposphere when suitable catalysts are present
4. Tropospheric ozone contributes to photochemical smog
5. Photochemical smog causes respiratory problems/ eye & nose irritation