Why do the CFC's reach the ozone?
The stability of CFC molecules means that CFCs can only be broken down by UV radiation found above the ozone layer.
Give the initiation stage of the depletion of the ozone when the CFC molecule reaches the stratosphere.
CFCl3 -----------> Cl* + *CFCl2
Give the propagation steps for the depletion of the ozone with CFC's.
The breakdown of ozone takes place in two propagation steps:
1) Cl* + O3 ---------> ClO* + O2
2) ClO* + O -----------> Cl* + O2
O3 + O ------> 2O2
Give the propagation steps for the *NO radical that destroys the ozone.
As with chlorine radicals, the breakdown of the ozone proceeds in two propagation steps:
1) *NO + O3 -------> *NO2 + O2
2) *NO2 + O -----> *NO + O2
Overall: O3 + O -----> 2O2
How is *NO produced?
Comes from lightning or aircraft engines.
What are the three main atmospheric pollutants the internal engine of a car emits?
- Carbon monoxide
- Oxides of nitrogen
- Unburnt hydrocarbons
How is carbon monoxide produced and what are its dangers?
1) Created by incomplete combustion from traffic pollution
2) The haemoglobin in our blood carries oxygen around the body. Carbon monoxide binds strongly with the haemoglobin, reducing the oxygen supply to the body.
How are the nitrogen oxides formed, and what are their dangers?
1) Nitrogen oxides are produced by the high temperature process combustion. as some of the nitrogen from the air is oxidised by oxygen. Two oxides of nitrogen are produced, there is nitrogen monoxide(NO) and nitrogen dioxide (NO2).
2) Nitrogen dioxide in the atmosphere is converted into nitric acid, a contributor to acid rain.
3) Nitrogen oxide are respiratory irritants.
How are unburnt hydrocarbons produced and what are their dangers?
1) Unburnt hydrocarbons come from unburnt fuels.
2) Unburnt hydrocarbons react with nitrogen dioxide to form low level ozone. Low- level ozone is a serious pollutant, causing breathing difficulties.
What are oxidation catalysts?
Oxidation catalysts are used on diesel engines to decrease emissions of carbon monoxide and unburnt hydrocarbons. Combined with complex filter systems, they also remove particulate matter.
Give the reactions which take place in an oxidation catalyst.
The following reactions take place:
2CO(g) + O2 (g) ------> 2CO2(g)
C12H26(l) + 18.5O2(g) -------> 12CO2(g) + 13H2O(l)
What is a three-way catalyst?
A three-way catalyst is fitted to petrol engines. In this system, nitrogen monoxide reacts with carbon monoxide to form non-toxic gases nitrogen and carbon dioxide.
Give the reaction that takes place in a three-way catalyst.
2NO(g) + 2CO(g) -----> N2(g) + 2CO2(g)
Explain how a three way catalyst functions.
The catalyst provides a surface on which the reaction takes place.
- The CO and NO gas molecules diffuse over the catalytic surface of the metal. Some of the molecules are held on to the metal surface by absorbtion.
- Temporary bonds are formed between the catalytic surface and the gas molecules. These bonds hold the gas molecules in the correct position on the metal surface, where they react together.
- After the reaction, the CO2 and N2 products are desorbed from teh surface and diffuse away from the catalytic surface.