The greenhouse effect - global warming:

  • Radiation from the sun reaches the planet.
  • The radiation is absorbed by the Earth and re emitted as IR radiation.
  • Most of this IR radiation goes back into space but some is absorbed by gases in the atmosphere.
  • These gas molecules absorb the IR radiation then re emit it as energy, this energy warms up the atmosphere.
  • These gases are:  water, methane and carbon dioxide.

How do gases absorb radiation?

  • Just like IR spectroscopy, the bonds in these greenhouse gases absorb IR radiation in their bonds.
  • The bonds vibrate absorbing the IR radiation.
  • Different gases will absorb different amounts of IR radiation.
  • 3 factors determine the impact a gas has on Global warming:
  1. Its concentration in the atmosphere
  2. Its ability to absorb IR radiation
  3. Its lifetime in the atmosphere
  • These 3 factors make up the GWP (Global Warming Potential)
  • The term Climate Change explains that although the average temperature of the planet is rising, different areas around the planet will suffer from extreme weather patterns.

Solutions to the Greenhouse Effect:

Carbon Capture and Storage, CCS:

  CH4(g) + 2O2(g) CO2(g) + 2H2O(g)        
  CH4(g) + 2H2O(g) CO2(g) + 4H2(g)        

Storage as carbonates:

  CaO(s) + CO2(g) CaCO3(s)            
  MgO(s) + CO2(g) MgCO3(s)            

The ozone layer

  • Ozone is 3 oxygen atoms joined together.
  • We are producing ozone where we don't want it and destroying it where we do want it.
  • Low level ozone in the troposphere causes respiratory problems.
  • The destruction of high level ozone allows harmful UV radiation to reach earth.
  • Ozone acts like a big pair of sunglasses filtering out most of the harmful UV radiation. 
  • Prior to the formation of ozone our planet was scorched and no life could survive.
  • UV radiation is divided into a, b, and c. 
  • C is the most harmful and is blocked out completely by ozone.
  • A is the weakest and only a small amount is absorbed by ozone.  This is the one that gives you a tan and ages your skin prematurely.

Ozone formation:

  O2(g) + UV 2O(g)            
  O(g) + O2(g) O3(g) + Heat        

How the ozone layer works:

  O3(g) + UV O2(g) + O(g)        
  O(g) + O2(g) O3(g) + Heat        
  O(g) + O2(g) D O3(g)            

Removal of ozone:

  O(g) + O3(g) 2O2(g)            

Ozone depletion

1)  CFC's:

             CF2Cl2                      CF2Cl.       +          Cl.

             Cl.              +                O3                          ClO.           +                    O2              Step 1

 

             ClO.           +                O                            Cl.              +                    O2              Step 2

 

Overall

 

  O(g) + O3(g) 2O2(g)            

2)  Nitrogen oxide:

             .NO              +                O3                           .NO2            +                    O2              Step 1

 

             .NO2           +                O                            .NO              +                    O2              Step 2

 

Overall

 

  O(g) + O3(g) 2O2(g)            

Controlling air pollution

The internal combustion engine:

1)  Carbon monoxide:

2)  Nitrogen oxides (NOx):

3)  Unburnt hydrocarbons:

The catalytic converter:

1)  Oxidation catalytic converters - diesel engines:

  2CO(g) + O2(g) 2CO2(g)            
  C12H26(l) + 18.5O2(g) 12CO2(g) + 13H2O(g)        

2)  3-way catalyst - petrol engines:

  2NO(g) + 2CO(g) N2(g) + 2CO2(g)        

How the catalyst functions:

Adsorption:  As the molecules diffuse over the surface of the catalyst some of the molecules are held on the metal surface.
Reaction:  Temporary bonds are formed between the molecules and the surface of the catalyst.  This weakens the bonds in the molecules.  The molecules can now react.
Desorption:  After the reaction the products are desorbed from the catalyst and diffuse away.

Green chemistry

Sustainability and the green chemist

The 12 principles:

1)  Prevention

2)  Atom economy

3)  Less hazardous chemical synthesis

4)  Design safer chemicals

5)  Safer solvents and auxiliaries

6)  Design for energy efficiency

7)  Use of renewable feedstocks

8)  Reduce derivatives

9)  Catalysts

10) Design for degradation

11) Real time analysis for pollution prevention

12) Inherently safer chemistry for accident prevention

 

CO2 - villain to saviour

Using CO2

1)  In foam:

2)  As a solvent:

a)  Decaffeinating coffee:

b)  Extracting beer flavour:

c)  Dry cleaning:

d)  Toxic waste treatment:

e)  For chemical synthesis: