The Atmosphere F332 with ideas

Includes all of the Storyline information from The Atmosphere module in F332 Chemistry Salters OCR, natural resources.

It also includes all of the relevant Chemical Ideas, with 10 questions at the end of each storyline sub-topic.

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  • Created by: Xavier
  • Created on: 15-05-12 13:36
Preview of The Atmosphere F332 with ideas

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Xavier
Chemistry Revision
The Atmosphere
Storylines
A1 ­ What's in the air?
A2 ­ Screening the Sun
A3 ­ Ozone: A vital sunscreen
A4 ­ The CFC story
A5 ­ What is the state of the ozone layer now?
A6 ­ The greenhouse effect
A7 ­ Trouble in the troposphere ­ what happens if concentrations of
greenhours gases increase?
A8 ­ Keeping the window open ­ role of water vapour
A9 ­ Focus on carbon dioxide
A10 ­ Summary
Ideas
5.2 ­ Molecules and Networks
6.2 ­ What happens when radiation interacts with matter
6.3 ­ Radiation and Radicals
7.1 ­ Chemical Equilibrium
10.1 ­ Factors affecting reaction rates
10.2 ­ The effect of temperature on rate
10.5 ­ What is a catalyst?
10.6 ­ How do catalysts work?
A1 ­ What's in the air?
1

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Page 2

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Xavier
The atmosphere is a thin layer of gas extending 100km above Earth's surface
Chemically important regions are the troposhphere and stratosphere.
As altitude increases, density decreases.
90% of molecules in the atmosphere lie in the lower region called the troposphere.
The concentrations of substances are either measured as percentages or as parts per million.
PPM is used when concentrations are small.
Gases and main human sources...…read more

Page 3

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Xavier
Mixing is different in the reverse temperature gradient of the stratosphere: mixing rarely occurs
in the vertical direction, but does occur in horizontal circulation.
6.2 ­ What happens when radiation interacts with matter?
EM radiation transfers energy to chemicals.
These chemicals absorb energy and changes occur.…read more

Page 4

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Xavier
Vibrational energy: corrresponds to IR
(we sense IR as heat, bonds in chemicals in our skin vibrate more energetically, the energy is
converted to KE which warms us up).
Rotational energy: corresponds to a lower frequency radiation ­ Microwaves
Translational energy: is even less, it is so small that e can treat it as being continuous.…read more

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Page 6

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Xavier
The sun radiates a wide spectrum of energy.
Some corresponds to the energy required to break chemical bonds ­ even in DNA.
This can cause damage in genes and cause skin cancer.
Years of exposure can make people look wrinkly and leathery: radiation damages proteins of
connective tissue beneath the skin.
Many materials called `sunscreens' absorb UV; the most damaging part of the spectrum. E.g. glass
­ you won't get sunburnt if you are inside near a window.…read more

Page 7

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Xavier
All reactions involve the breaking and remaking of chemical bonds.
Bond breaking = bond fission
Two types = Heterolytic fission and Homolytic fission
Heterolytic fission
Both shared electrons go to just 1 atom
Two ions are formed
It is common when a bond is already polar
E.g.…read more

Page 8

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Xavier
Even O2 has two unpaired electrons, and so is a biradical: however it is relatively stable.
Radicals are reactive. Filled outer electron shells are more stable than unfilled ones.
When a Cl radical collides with a H2 molecule, it will steal the electron from the H2 bond and form
HCl and a H radical.
This is the same for methane and a chlorine radical:
This is a propagation reaction. The initiation reaction would be getting the radical in the first place.…read more

Page 9

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Xavier
CH3Cl + Cl2 CH2Cl2 + HCl
For every Cl2 molecule used, 1 H atom is replaced on the halogenoalkane, and one HCl (H-Hal) is
formed.
In summary,
Radical chain reactions usually occur in the gas phase or in a non-polar solvent
They are often initiated by heating or by light, and go very fast
Questions
1. How did suntanning become popular? What defines a good sunscreen?
2. What is dangerous about radiation?
3.…read more

Page 10

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Xavier
Ozone is being made and destroyed all the time.
If left to themselves, the rate of proucing ozone = the rate of destroying ozone.
I.e. they are in a "steady state." But not with human inteference!
Reaction (2) should equal reactions (4) and (5). However, when taking measurements we are
aware that this is not the case. In fact, more ozone is being destroyed than is being created.
More about this later..…read more

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