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The Atmosphere


A thin layer of gases that form a protective
covering around the planet
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0383% (383ppm)
 Gases can be measured in % volume or ppm
(parts per million by volume)
To convert ppm to % :
ppm ÷ 10 000
To convert % to ppm :
% x 10 000
 Human activity has added more gas to the
atmosphere, increased certain concentrations of
natural gasses to levels now counted as
pollutants as well as introducing pollutants
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 Atmospheric Pollution is a global problem due to
air currents and prevailing winds
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Power stations, vehicles),
Deforestation
Cattle Farming, Landfill sites, Rice Fields,
Natural Gas Leakage
Fertilised soils, changes in land use (eg
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Car exhausts)
Combustion of hydrocarbon fuels (from the
reaction of N2 and O2)

Rate of ozone production = rate of destruction of ozone (STEADY STATE)
Oxygen atoms aren’t the only radicals breaking down ozone
Troposphere:
 Is a Respiratory irritant/toxin
 Contributes to photochemical smog
 Is a greenhouse gas
CO + NOx + HCs + Sunlight  Ozone + other products
Some radicals are produced by natural processes, others by human activity:
Cl∙ - CH3Cl from oceans, CFCs
Br∙ - CH3Br from volcanic eruptions, forest fires, bromoalkanes
∙NO - combustion engines, power stations, airplanes, nitrogenous fertilisers
∙OH - from water
Monitoring the ozone layer:
UV spectroscopy is used to measure the amount of UV radiation absorbed by the
atmosphere
The ozone layer is measured in Dobson units (DU): 1 DU ≡ 0
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Extremely cold conditions and
strong winds create Polar vortex over the poles, Polar stratospheric clouds (PSCs) – ice crystal clouds then form
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g
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g
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g
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The average Earth
temperature is near constant
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034
CO2 and H2O absorb in two ‘bands’ of the
Fuels
Earth’s radiation spectrum
H2O Evaporation of oceans/lakes 0
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1
Between these two bands is a ‘window’ where
CH4
Intensive livestock farming,
30
0
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00001
N2O and CFCs
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0003
radiation – global warming potential, GWP
Greenhouse gas concentrations are rising
Scientists predict that the earth’s temperature could rise 2
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high mp/bp, insoluble in water, doesn’t conduct electricity
Rate of Reaction = Change in concentration/time (units mol dm-3s-1)
Collision theory:
 Reactions occur when:
o reactant particles collide
o in the correct orientation
o with a minimum K
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≥ Activation enthalpy, Ea
Activation enthalpy, Ea = the minimum K
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E
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Collisions are more
frequent & have more energy ≥ Ea so reaction rate increases
 Catalyst: Provides a pathway with a lower activation enthalpy
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Fast reactions
have a low activation enthalpy
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 At any temperature the kinetic energies are spread over a wide range
 Area under curve = Total number particles
 At any given time only a fraction of the particles have energy ≥ Ea
 Increasing the temperature flattens and shifts the distribution curve to the
right
 Increasing the temperature of a reaction:
 The reactant particles gain K
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Chlorine Radicals in
the breakdown of Ozone to Oxygen)
Reactants + catalyst → intermediate
Intermediate → products + catalyst

Uses of Catalysts – Industry
 Allow reactions to take place at
lower temperatures
 Enable different reactions to be
used
 Are often enzymes
 Economic Importance in production:
Poly(ethene), Sulphuric Acid, Ammonia, Ethanol
 Can Reduce Pollution:
Catalytic Convertors
Radiation and Matter
Changes occur in molecules when they absorb certain frequencies of
radiation
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+ Y
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O atom) is a Bi-radical
Radical Reactions:
~ Occur in the gas phase / non-polar solvent
~ Initiated by light or heat
~ Very Fast
Eg
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Initiation: A molecule absorbs high energy UV radiation,
homolytic fission occurs forming radicals, always endothermic
2
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Termination: Radicals combine, forming a stable molecule,
always exothermic
Radical Halogenation of Alkanes:
Depending on concentrations of halogen, the final product may change (CH4 or CCl4)
Photodissociation of Bromine:
When bromine is exposed to light photodissociation occurs where the Br–Br bond is broken homolytically and two
Bromine radicals are formed
These radicals are then able to react via a substitution reaction with hexane
This reaction of bromine causes it to lose its colour



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