4 - The Ozone Story (OZ) Flashcards
(32 cards)
Define bond fission
Breaking of a covalent bond
Define heterolytic fission
Electrons distributed unequally to form 2 different ions
Define homolytic fission
Electrons distributed equally to form 2 uncharged radicals
What does double headed arrow represent in bond fission?
Movement of electron pair
What does a single headed arrow represent in bond fission?
Shows movement of a single electron
1st step of a free radical chain reaction
Initiation:
-2 radicals produced with photochemical reactions
-bond breaks homolytically
2nd set of free radical chain reactions
Propagation:
-radical reacts with a non-radical molecule
-new radicals are created which then go on to react with other non-radicals
3rd set of free radical chain reactions
Termination:
-2 radicals react and form a non-radical molecule
-ends chain reaction
Define photochemical reaction
Using visible light or UV in a reaction
Define photodissociation
Sunlight breaking bonds
Trend of boiling points for haloalkanes
-Increases going down group
-Explained by instantaneous-induced dipoles, halogen atom larger with more electrons and stronger dipole
Initiation of forming haloalkanes
-Br-Br broken by photodissociation
-Bond breaks via homolytic fission
-Br - Br —> Br• + Br•
(single arrow to both Br from bond)
Propagation of forming haloalkanes
-Br radical reacts with a methane molecule to make a methyl radical
-Methyl radical reacts with Br2 to form bromoethane and a Br radical
-Br radical can react with more methane
-Br• + CH4 —> HBr + •CH3
(single arrow between space and between H-C)
-•CH3 + Br - Br —> CH3Br + Br•
(single arrow between space and -Br)
Termination of formation of haloalkanes
-2 radicals react to make a stable non-radical molecule
-Example: forming bromoethane
-H3C• + •Br —> CH3Br
(single arrows pointing to space between reactants)
Initiation of CFCs destroying ozone
-C-Cl bond broken by photodissociation in a CFC molecule
-CCl3F + hv —> CCl2F• + Cl•
Propagation of CFCs destroying ozone
-Cl• reacts with O3 to form ClO• intermediate and O2
-Intermediate reacts with O to make O2 and Cl•
-Cl• + O3 —> O2 + ClO•
-ClO• + O —> O2 + Cl•
Termination of CFCs destroying ozone
-2 radicals react to make a stable non-radical molecule
-Example: Forming Cl2
-Cl• + Cl• —> Cl2
Overall reaction of CFCs destroying ozone
O3 + O —> 2O2
-Cl• catalyst
-ClO• formed and used, cancelled
What does a Boltzmann distribution show?
Distribution of energy of all particles involved at a particular temperature
What are the x & y-axis of a Boltzmann distribution?
x = Energy
y = Number of molecules
What does a curve higher and closer to the y-axis mean?
-Temperature = lower, higher proportion of molecules have lower energy
-Fewer molecules have energy greater than E[a]
What can CFCs do to ozone?
Break it down
What are CFCs (chlorofluorocarbons)?
Molecules that have had all hydrogens replaced with F/Cl
What CFC bonds can be broken in the stratosphere?
C-Cl by UV
