The ozone layer
The Ozone Layer absorbs much of the harmful ultraviolet radiation emitted by the sun, which, if it were to reach the Earth’s surface unimpeded, would cause burning and skin cancer (also vitamin D ☺)
Ozone, O3 is constantly formed and broken down. An equilibrium with O2 and O* is present.
Overall Equation: O3 ⇌ O2 + O
O3 + (UV Rad) → O2 + O* O2 + O* → O3
These two reactions would maintain a steady rate if undisturbed.
But:
1- CFC’s make Cl* by breaking down in atmosphere.
Cl* + O3 → ClO* + O2
ClO* + O → Cl* + O2
The radical reacts with the Ozone to produce ClO*. This
reacts with O to form a chlorine radical and oxygen.
2- NO* can be formed from thunderstorms and aircraft
where there is enough energy (N2 + O2 → 2NO*)
NO + O3 → NO2 + O2
NO2 + O → NO + O2
The Overall Reaction is just:
O3 + O → 2O2
Which means there is less ozone to absorb the UV radiation and continue the equilibrium in the ozone layer. Hence less protection for us. Oh no!
Air pollution
Air pollution offers a more direct threat to us, rather than long-term climate change.
Infrared Spectroscopy is used to measure air pollution. A
sample of air is drawn into the spectrometer. A beam of
infrared radiation of a certain frequency is passed through the sample. Any CO present will absorb this CO. A control reading is taken with ‘normal’ air and compared.
Burning
hydrocarbons in fuels will produce carbon dioxide. If
oxygen is not present, incomplete combustion will occur a and CO will be produced. (It is toxic and combines with the red blood cells in the body instead of oxygen)
Some hydrocarbons don’t get burnt and escape unchanged. They are toxic.
Oxides of nitrogen are formed as the N ≡ N bond from N2 in the air breaks in the hot
engine. Oxides of nitrogen can cause smog and acid rain. Exactly like the aircraft
example in the atmosphere; N2 + O2 → 2NO
- These oxides of nitrogen contribute to SMOG and ACID RAIN.
A catalytic converter reduces the amount of these 3 gasses emitted from a vehicle.
1) ADSORPTION: Reactant molecules arrive at the surface and bond with the solid
catalyst.
2) Bonds between the reactants atoms are weakened and they break up. This forms
radicals. These radicals join up and make new molecules
3) DESORPTION: The molecules are released from the catalyst.
Hence it is a heterogeneous catalyst and made from Rhodium, Platinum or Palladium.
Sustainable chemistry
Many industries aren’t that sustainable. Plastics come from crude oil, which a non-
renewable resource. The products themselves are not bio-degradable and hard to recycle. You can use renewable raw materials such as plastics from plant oil
You can use renewable energy sources such as wind, solar, tidal, wave etc.
Role of the chemical industry
- Chemical processes should have a good percentage yield. This means we can
produce as much as possible of the desired product.
- A high atom economy is also a must, as this means the companies do not have to
get rid of unwanted products (which are often polluting gasses). Most of the time,
the products are recycled in a new industry.
- Addition reactions have a high atom economy and substitution reactions don’t.
Hence it is better to use addition reactions.
- The number of steps should be kept down, as this often minimises production of
waste materials and increases percentage yield.
- Catalysts are pretty awesome. They improve the atom economy and (think
enthalpy) make it so the yield is the same for a lower temperature which reduces
cost to the manufacturer and reduces demand for energy which is from fossil
fuels.
Chemicals should be as non-toxic as possible. For example lead was used in paint but
it had nasty effects on your health, so lead-free compounds are used instead
Some foams in fire extinguishers leave hazardous products behind including CFC’s (→
Cl*). Alternatives are available.
Dry cleaners use a solvent based on chlorinated hydrocarbons, but they are
carcinogenic. Safer alternatives are now available.
Ethanol and Methanol can be used for fuels. Already, they are mixed with normal
petrol in the UK. They can be derived (Fermentation > Steam hydration) from plant
matter/Vegetable oil which is renewable. It is cleaner than petrol.
