Ozone Story - Radicals Flashcards
What is the troposphere?
the lower layer of the atmosphere
What is the stratosphere?
the upper layer of the atmosphere, 15km above sea level
Why doesn’t nitrogen absorb radiation well?
it has a very strong triple bond that requires a lot of energy to make it vibrate
How do you convert between ppm and % of the atmosphere?
ppm -> %
x 10,000
What is ppm?
particles per million
unit of measuring how much of a gas is present
What are the 4 effects that radiation can cause in molecules?
Electronic energy
Vibrational energy
Rotational energy
Translational energy
Which type of radiation causes electronic energy in molecules?
UV / visible light
Which type of radiation causes vibrational energy levels?
infrared radiation
Which type of radiation causes rotational energy levels in molecules?
microwaves
Which type of radiation causes translational energy levels in molecules?
microwave / radio
What is electronic energy?
energy that affects the electrons only
What is vibrational energy?
energy that causes the bonds to vibrate
What is rotational energy?
energy that causes the whole molecule to rotate
What is translational energy?
energy that causes the whole molecule to move around
Does exciting electrons require more or less energy than moving a molecule as a whole?
significantly more
What happens to halogens in the stratosphere?
they are ionised by UV radiation and the diatomic molecules are split into radicals
What is a radical?
a chemical with an unpaired electron
What is the general reactivity of radicals?
they tend to be reactive
What is homolytic bond fission?
Breaking a bond equally, so each molecule recieves an equal number of electrons
How are photons commonly represented in atmospheric chemistry?
hν
What is heterolytic bond fission?
breaking a bond unequally
What is the reaction for Bromine undergoing homolytic bond fission?
What is the reaction for a compound undergoing heterolytic bond fission?
What is photochemical dissociation?
the reaction where a chemical is broken down by a photon
What are the 2 reactions that show the formation of Ozone?
O2 -> O. + O.
O. + O2 -> O3
What 3 things can happen to an oxygen radical after being dissociated?
react with O2 to form ozone
react with another oxygen radical to form O2
react with ozone to form 2O2
What is the most likely reaction an oxygen radical will undergo and why?
react with O2 to form ozone
there is a majority of O2 compared to oxygen radicals or ozone, so it is more likely to collide with the O2
Is the formation of ozone endothermic or exothermic?
exothermic
What is the reaction for the decomposition of ozone?
O3 -> O2 + O.
What is the initiation step in the radical chain reaction for hydrogen halides?
X2 + hν -> 2X.
What are the propogation steps for the chain reaction of hydrogen halides?
X. + H2 -> HX + H.
H. + X2 -> HX + X.
What are the termination steps for the chain reaction of hydrogen halides?
H. + H. -> H2
X. + X. -> X2
H. + X. -> HX
What is the overall effect of the radical chain reaction between hydrogen and a halogen?
H2 + X2 -> 2HX
What is a termination reaction?
any reaction where 2 radicals react, resulting in products with no radicals
What is the initiation step for the radical chain reaction between a halogen and methane?
X2 + hν -> 2X.
What are the propogation steps for the radical chain reaction between methane and a halogen?
X. + CH4 -> HX + CH3.
CH3. + X2 -> CH3X + X.
What are the termination steps for the radical chain reaction between methane and a halogen?
X. + X. -> X2
CH3. + X. -> CH3X
CH3. + CH3. -> C2H6
How can ozone be removed from the atmosphere?
radicals in general but particularly:
Br
Cl
OH-
NO
What is the chain reaction for the removal of ozone with a radical?
X = Cl, Br, NO or OH-:
X. + O3 -> XO + O2
XO + O. -> X. + O2
O. + O3 -> 2O2
