Ozone in the stratosphere and CFC's Flashcards
Is oxygen a radical
it is a biradical because it contains 2 unpaired electron (use electron configuration and boxes to see)
How is ozone formed
in the stratosphere some O₂ absorb high energy uv present in the radiation arriving at earth from the sun, this causes them to photodissociate. The sperate oxygen atoms formed can then react with more oxygen molecules forming ozone
Equations of how ozone is formed
O₂ + hv -> O + O (both are biradicals but is just written as O)
O + O₂ - > O₃
How does ozone breakdown
some ozone breaks down when it absorbs high energy uv radiation. Some ozone molecules break down when they collide with sperate O atoms and radicals act as catalyst
Equations of how ozone is broken down
O₃ + hv -> O₂ + O
O₃ + O -> 2O₂
Why is ozone important
because it is responsible for vital sunscreening. Preventing high energy uv from the sun reaching earth’s surface where it could cause skin cancer, eye problems or damage to plants
Why isn’t there usually ozone in the troposphere
uv radiation isn’t high enough to frequency to break the oxygen bonds
Ozone conc (usually)
ozone is being made and broken down all the time, so it reaches a point where the rate of production equals the rate of destruction. Steady state so con stays constant
CFC’s definition
chlorofluorocarbons - manmade molecules of carbon, chlorine and fluorine only
Why were CFC’s popular
non-toxic, non-flammable, very unreative, cheap, overall safe
What were CFC’s used for
refrigerants, blowing agents for foam packaging, propellant for aerosol sprays, solvents for cleaning
What was the problem with CFC’s
they were too unreactive so they would survive in the atmosphere long enough to reach the stratosphere where the high energy uv from the sun ensures they do react. The CFC molecules absorbs high energy uv and photodissociates (bond breaks by homolytic fission giving radicals)
Why else were CFC’s bad in the atmosphere
they produced chlorine radicals which acted as a catalyst for the breakdown of ozone
What are the equations which shows that chlorine radicals from CFC’s cause ozone destruction
Cl* + O₃ -> ClO* + O₂
ClO* + O -> Cl* + O₂
How to show that chlorine radicals act as a catalyst using the equations
add up both sides
Cl* + O₃ + ClO* + O -> ClO* + O₂ + Cl* + O₂
and cancel out any thing that doesn’t change
O₃ + O -> 2O₂
(chlorine radicals are used then regenerated = catalyst)
What have we replaced CFC’s with and why
HCFC’s - contain C-H bond which makes it much less stable so break down before reaching stratosphere
HFC’s - contain C-H bond but also do not have a C-Cl bond to break so can never make chlorine radicals.
But both are greenhouse gases contributing to climate change
Give examples of other radicals which can cause the breakdown of ozone
bromine radicals, OH, NO
