Unit 3 Section 2

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Two types of cracking
Thermal, catalytic
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Conditions for thermal cracking
high temp ~ 1000 *C high pressure ~ 70 atm
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products of thermal cracking
lots of alkenes, useful for polymers
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Catalytic cracking contitions
zeolite catalyst (hydrated aluminosilicate) at slight pressure and high temp ~ 500*C
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products of catalytic cracking
mainly aromatic hydrocarbons and alkanes needed to produce motor fuels
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Pollution from burning fuels
nitrogen oxides, sulfur dioxide
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how is nitrogen monoxide produced
high pressure and temperature in car engine cause nitrogen and oxygen atoms from the air to reacct together.
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how does nitrogen monoxide react further
N2+O2-->2NO THEN 2NO + O2 --> 2NO2 (forms nitrogen dioxide)
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nitrogen oxides are
toxic and posonous molecules
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Engines dont always...
burn all the fuel molecules
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This leads to
some of the unburnt fuel molecules reacting with Nitrogen oxides in presence of sunlight to form ground level O3 (major component of smog)
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Problems with ground level ozone
irriates people's eyes, aggravates respiratory problems and even causes lung damage
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3 main pollutants from vehicle exhausts
nitrogen oxides, unburnt hydrocarbons, CO
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How does a catalytic converter work
very large surface areas to make sure that the harmful pollutants have the best chance of reacting to form less harmful chemicals
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How does catalytic converter remove unburnt hydrocarbons
e.g C3H8 + 5O2 ----> 3CO2 + 4H2O (just complete combustion)
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How does catalytic converter remove nitrogen oxides
2NO --> N2 + O2 and 2NO + 2CO ----> N2 + 2CO2
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sulfur dioxide does what when gets into atmosphere
dissolves in moisture and is converted into sulfuric acid (acid rain) same process occurs when Nitrogen dioxide goes into atmosphere (nitric acid)
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acid rain does what
destroys trees/vegeatation, and corrodes buildings and statues, and kills fish in lakes.
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How to remove SO2 from power station flue gases before gets into atmosphere
Powdered calcium carbonate or calcium oxide mixed with water to make alkaline slurry. when flue gases mix with alkaline slurry, harmless salt is formed (calcium sulfate) {CaO + SO2 --> CaSO3}
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Other cards in this set

Card 2

Front

Conditions for thermal cracking

Back

high temp ~ 1000 *C high pressure ~ 70 atm

Card 3

Front

products of thermal cracking

Back

Preview of the front of card 3

Card 4

Front

Catalytic cracking contitions

Back

Preview of the front of card 4

Card 5

Front

products of catalytic cracking

Back

Preview of the front of card 5
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