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In the air there are 4 main gases: (Percentage to PPM= x10000)
Depending on the energy, molecules show different behaviours. In increasing order;
Translational, molecule moving around as a whole; Rotational, molecule rotates; Vibrational, the
bonds in the molecule vibrate; Electronic, the electrons move from one shell to the next.
Energy Change Radiation absorbed
The energy can excite the electrons, they will then return to their ground state. It can remove an
electron from the molecule, ionising it or it can break chemical bonds, known as
When a covalent bond is split, the shared electrons
are distributed in 2 ways. In heterolytic fission, they go
to the same atom, creating 2 ions. In homolytic
fission, the electrons go to different atoms, resulting
in radical production. Radicals have an unpaired
electron and so a very reactive. There are 3 process,
initiation, the making of a radical. Propagation,
where there are product and reactant radicals.
Termination where two radicals collide. Shown chlorine displacing a hydrogen.
Radicals play a key part in the destruction of ozone. It is a catalytic cycle as the chlorine radicals act
as a catalyst with 1 chlorine molecule being able to remove 1 million ozone molecules. Ozone
depletion is a natural process, as is ozone production but the use of CFC means there are more
chlorine radicals in the air which cause a faster ozone depletion.
These chlorine radicals are produced by photo-dissociation of CFC's. This occurs in the
stratosphere, this is when the photons are of the correct frequency to break the bonds. At first
scientists thought that they had made a mistake because of the amount of depletion according to
experimental results. Replacements for CFC's include Hydrochlorofluorocarbons and
hydrofluorocarbons. Both of these are broken down in the troposphere not stratosphere however
both are also greenhouse gases and so contribute to global warming. Alkanes can also be used.
They do not contain chlorine, however they are also a greenhouse gas. Ozone is important because
it absorbs much of the high energy UV that causes skin cancer. Ozone in the troposphere can cause
Dynamic equilibriums can be achieved if the rate of the forward and reverse reactions in a
reversible reaction are going at the same rate. This can only occur in a closed system. In open
systems, steady states can be achieved across a few reactions so that concentrations of all
reactions and products stay the same.
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Global warming occurs as solar energy reaches the earth as UV and visible light. The earth absorbs
this, heats up and emits IR. The gas molecules bonds absorb this and gain more KE by colliding more
and so raise their temperature. The molecules emit some IR which heats up the earth. More
greenhouse gases means an enhanced global warming. Carbon dioxide concentrations could be
reduced by increasing photosynthesis, reducing fossil fuel use and use renewable or by burying and
reacting it.…read more
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Chemistry Notes…read more