Module 4 chemistry OCR summary

Hopefully I've written some quite consise notes that covers all the information you need to know for module 4 of UNIT 2 of AS Chemsitry for OCR. Really hope it helps! The information can be found in more detail in my powerpoint which is based on information provided by the OCR AS text book. Good luck everyone!

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Module 4 summary ­ chemistry
Greenhouse effect is the process which the absorption and subsequent emission of infrared
radiation by atmospheric gases warms the lower atmosphere and the earth's surface i.e.
bonds within the molecules of greenhouse gases absorb infrared radiation, causing the
molecules to vibrate, which subsequently emits infrared radiation that is either absorbed by
other gas molecules of the surface of the earth
The amount a gas contributes to the greenhouse effect depends on its concentration in the
atmosphere and the ability for the bonds to absorb infrared radiation
Carbon dioxide, methane and water vapour are the three major greenhouse gases
GWP stands for the global warming potential. Gases in the atmosphere are given a rating of
The effects of global warming can be appreciated by everyone such as the more destructive
storms that are also becoming more frequent in tropical rainforests and the melting of ice
and permafrost the Arctic
Global warming brings unpredictable changes such as flooding of low lying land
In 1997, the Kyoto Protocol was introduced which committed 100 countries to reduce their
emissions of 6 greenhouse gases by 5% by 2012. However, the biggest emitter (the USA)
did not sign to this
CCS is carbon capture storage which is seen as a direct way of getting rid of waste carbon
dioxide gas. There are three methods:
o Injecting into oil gas and oil fields deep under the oceans
o Reacting with metal oxides to form metal carbonates
o Being absorbed by porous rock types
Ozone is a molecule that consists of three carbon atoms. It can be both good and bad. It is
good when it is in the stratosphere which is the second layer of the earth's atmosphere.
Here it prevents the entrance of harmful UV. The bad layer is the troposphere which is the
layer of the atmosphere that is closest to the earth's surface. It can cause respiratory
Three different types of UV:
o UV-a is between 320-400nm which is not very damaging to organisms than UV of
shorter wavelengths, and so able to pass straight through to the earth's surface
o UV-b is between 280-320nm. Some of this reaches the earth's surface, and can
cause sun burn, and sometimes genetic damage which can lead to skin cancer if
exposure is prolonged
o UV-c is between 200-280nm but is completely screened out by the ozone layer
Ozone forms when UV radiation that is less than 240nm provides the energy to break an O2
molecule into two O atoms. These O atoms are then able to rapidly react with an O2
molecule to form an O3 molecule, which produces heat
The ozone layer works by absorbing UV between 240-310nm, which converts O3 molecules
back into an O2 molecule and an O atom, and then the process begins again
Ozone is removed when an oxygen atom and ozone molecule combine to form two O2
Cl. Radicals are formed when a C-Cl bond is broken in the upper stratosphere by UV
radiaition. The C-Cl bond is part of a CFC molecule, such as trichlorofluromethane. These

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O2 molecules:
o Initiation CFCl3 -> CFCl2. + Cl.
o Propagation 1 Cl. + O3 -> ClO. + O2
o Propagation 2 ClO. + O -> Cl. O2
o Overall O3 + O -> 2O2
NO. (nitrogen oxide) radicals can also be produced in aircraft and lightning and can break
down ozone:
o Propagation 1 NO. + O3 -> NO2. + O2
o Propagation 2 NO2 + O -> NO.…read more

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For decaffeinated coffee ­ removing the effects of the caffeine, without altering the
taste or being toxic
o For beer
o For dry cleaning without the use of toxic solvents, as supercritical CO2 also has
grease-dissolving properties that are needed in dry cleaning
o For toxic waste treatment, as many organic compounds dissolve in supercritical CO2
o For chemical synthesis…read more



There's a mistake! It says the ozone layer is made up of 3 Carbon atoms when it's actually 3 Oxygen atoms! Besides that this was quite helpful, Thanks  

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