Lecture 33 Gases VIII The Atmosphere

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Lecture 33 - Gases VIII - The Atmosphere
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Smog

• Historically, Smoke Fog
• Urban smog a soup of oxidants, hydrocarbons
  (HCs) and aerosols
• NOx HCs light smog

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L.A. smog city

• 1. Lots of cars ( NOx HCs)
• 2. Lots of sunlight
• 3. Bowl shaped geography
• 4. Frequent temperature inversions

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Temperature inversions
T inversion (very stable)
z
usual
T
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Ground Level Ozone

• Ozone is cool (in the stratosphere)
• Ozone is not cool (in the air we breathe)

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Ground Level Ozone

• XO3 Symptom
• 5 x 10-8 headaches
• 1 x 10-7 eye irritation
• 2.7 x 10-7 coughing
• 2.9 x 10-7 chest pain

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September, 1979

• 10 consecutive days with
• XO3 gt 3.5 x 10-7

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The smog sequence

• 1. Cars HCs NO

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Wheres the NO from?

• N2(g) O2(g) 2 NO(g)
• DGo 86.6 kJ/mol at 25oC

Kp exp (- DGo/RT)
6.6 x 10-16
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(pNO)2
Kp
pN2
pO2
(pNO)2 Kp
pN2
pO2
6.6 x 10-16 (0.78)(0.21)
in air
(pNO) 1.0 x 10-8 atm
in exhaust
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Formation of Ozone at Ground Level

• (2) HCs NO hn NO2 other stuff

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Radicals

• O atoms are radicals
• 1s22s22p4
• (2 short of an octet)
• thus, O is a strong oxidant

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Formation of Ozone

• (3) NO2 hn NO O

radical species (very reactive)
visible light
(4) O2 O O3 (5) NO ½ O2 NO2 (NO2 back!)
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Net Smog Reaction

• add reactions 3, 4 and 5
• 3/2 O2 hn O3

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Brownish Color of Smog

• 2 NO2 N2O4

brownish
colorless
DHo lt 0
equilibrium shift upon increasing T
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Acid Rain

• 1. Produce SO2(g)
• S(in coal) O2(g) SO2(g)
• or
• NiS(s) 3/2 O2(g) NiO(s) SO2(g)

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Acid Rain

• 3. Form H2SO4
• SO3(g) H2O(l) H2SO4(aq)

a strong acid
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Whats the big deal about acid rain?

• 1. Lakes become acidic - fish dont like
• that.
• 2. Acid rain kills plant life.
• 3. Buildings dissolve.

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• CaCO3(s) H2SO4(aq)
• CaSO4(aq) H2O(l) CO2(g)

soluble, mechanically weak
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Other Interesting Gas Things...

• Air bags
• Refrigeration
• Supercritical Fluids

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Air Bags
D

• 2 NaN3(s) 2 Na(g) 3 N2(g)
• 10 Na(g) 2 KNO3(s)
• K2O(s) 5 Na2O(s) N2(g)
• K2O(s) Na2O(s) SiO2(s) a glass

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How do we cool gases to very low temperatures?
Use other gases! (Refrigeration)
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Pi
PfgtPi
Insulated Container
TfgtTi
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Compress a gas - it warms up
Expand a gas - it cools down
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Compressor
Expansion Valve
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Heat released
Compressor
Expansion Valve
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Heat released
Compressor
Expansion Valve
Heat Absorbed
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The best gases for refrigeration are CFCs!

• (Ozone eaters)
• Possible Solution The Sound Fridge

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The best gases for refrigeration are CFCs!

• (Ozone eaters)
• Possible Solution The Sound Fridge

Inert Gas
BIG speaker (160 dB)
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a standing (acoustic) wave
high pressure points (WARM!)
low pressure points (COLD!)
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Other neat gas stuff...

• If T is high enough, a gas can not be liquefied
  at any pressure
• happens if T gt Tc

critical temperature of gas
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G
L
TltltTc
TltTc
T³Tc