15.2 Organohalogen Compounds in the Environment
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What is an organohalogen?
molecule containing at least 1 HALOGEN BONDED to a CARBON CHAIN.
What is the use of organohalogens?
pesticide
Do organohalogen compounds break down naturally?
no
In what layer is the ozone layer located in & what does it consist of?
stratosphere ozone, O3
What type of energy does the ozone absorb?
UV, ultraviolet
In the ozone layer, what sort of reaction does ozone continually take part in?
equilibrium, ozone continually formed + broken O2 + O ⇌ O3 energy for this reaction is provided by UV radiation
What are the names of the steps in CFC breakdown in the ozone layer?
• PHOTODISSOCIATION • PROPAGATION 1 • PROPAGATION 2
What occurs during photodissociation of CF2Cl2?
CF2Cl2 ⟶ CF2Cl• + Cl• initiated by UV radiation
Why does the C–Cl bond break first during hydrolysis of a haloalkane?
It has the lowest bond enthalpy
What occurs in PROPAGATION 1 of ozone breakdown?
Cl• + O3 ⟶ ClO• + O2
What occurs in PROPAGATION 2?
ClO• + O ⟶ Cl• + O2
What does the Cl• act as during breakdown of CFl2Cl2
catalyst
What is the overall equation of ozone breakdown?
O3 + O ⟶ 2O2
What effect does the presence of CFCs have on the formation + breakdown of O3 into O2 + O?
Equilibrium shifts to the right Favours breaking of O3
How is photodissociation initiated?
UV radiation from the sun
Suggest a property that makes CF3Cl suitable as a propellant in aerosol:
volatile / gas / inert / low boiling point
Which bond is most likely to break first in CF3Cl & why?
C-Cl because it has the lowest bond enthalpy (chlorine has larger ionic radius, so weaker electrostatic attraction between positive nucleus + shared pair)