F322: Chemistry Of The Air And Green Chemistry Flashcards
What effects a gasses ability to contribute to global warming
Described by it’s GWP (global warming potential):
- How efficient it is at absorbing the IR radiation
- It’s residence time in the atmosphere
- It’s concentration in the atmosphere, thus it’s rate of formation
Describe the greenhouse effect
Infrared radiation is absorbed by the vibrating C=C, O-H and C-H bonds in CO2, H2O (vapour) and CH4 in the troposphere. The IR causes these bonds in the molecules to vibrate more, and this extra energy is passed onto other molecules via collisions, raising their KE and thus the overall temperature in the atmosphere.
The role of chemists in reducing global warming
1) Provide scientific evidence to government that global warming is taking place
2) investigate solutions such as CCS (carbon capture and storage, which involves capturing waste CO2 and storing it in deep underground rock/oceans) or reacting waste CO2 with metal oxides to form stable carbonate minerals.
3) Monitor progress of certain initiates such as the Kyoto principle (an agreement from large industrialised countries to lower greenhouse gas emissions.)
Positive ways CO2 can be used
1) instead of CFCs as a blowing agent for expanded plastics
2) liquid CO2 as a solvent for:
Decaffeination of coffee
Dry cleaning
Toxic waste treatment
Chemical synthesis
Why the ozone layer is needed
Essential for life on earth as it absorbs high energy UV radiation (UV-c (entirely) and UV-b) from the sun. A decrease in the ozone layer would lead to more harmful UV-b reaching the earths surface, increasing rates of skin cancer.
Describe the natural equilibrium of the breakdown and formation of ozone in the stratosphere
Zone is continuously being formed and broken down in the stratosphere by the action of UV radiation (O3 -> O2 + O) which then immediately reacts to form ozone again (O2 + O -> O3). As the rate of formation equals the rate of decomposition, the concentration of ozone in the stratosphere is maintained.
Describe how ozone is damaged
The breakdown of ozone is catalysed by chlorine radicals (from CFCs -> UV light breaks the C-Cl bond homolytically) and by nitrogen oxides radicals (from the reaction of N and O in the air during thunderstorms and from aircraft).
Show the equations for how chlorine radicals break down ozone
I: CFCl3 -> Cl. + .CFCl2 (UV radiation)
P1: Cl. + O3 -> ClO. + O2
P2: ClO. + O2 -> Cl. + O2
Overall: O3 + O -> 2O2
Show the equations for how nitrogen oxide radicals break down ozone
P1: .NO + O3 -> .NO2 + O2
P2: .NO2 + O -> .NO + O2
Overall: O3 + O -> 2O2
Name and describe the 3 atmospheric pollutants that come from the internal combustion engine
1) carbon monoxide (CO): toxic gas formed from the incomplete combustion of hydrocarbons (burning in a limited supply of oxygen)
2) nitrogen oxides (NO, NO2) formed when N and O in the air react at the high temperatures of the car engine. Acidic gasses that contribute to the formation of photochemical smog and ozone at low levels (which causes breathing difficulties) in the reactions:
NO2 -> NO + O then O + O2 -> O3
3) Unburnt hydrocarbons eg benzene (C6H6) which is carcinogenic
What technique is used to monitor air pollution?
Infrared spectroscopy
Purpose of catalytic converters
Decrease carbon monoxide and nitrogen monoxide emissions from internal combustion engines.
Elements in catalytic converts
Platinum
Palladium
Rhodium
Describe the action/process of the catalyst in a catalytic converter
1) the CO and NO molecules diffuse over the catalytic surface of the metal and are help to the surface by ADsorbtion
2) the bonds between the molecules are weakened, lowering the Ea
3) the reaction takes place
4) the CO2 and N2 molecules are desorbed and diffuse away.
The equation that takes place in a catalytic converter
2NO2 + 2CO -> N2 + 2CO2
