11_Chapt18_1

11_Chapt18_1 - Gases and the atmosphere Chemical reactions...

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Mary J. Bojan Chem 110 Gases and the atmosphere Chemical reactions in the atmosphere Ozone cycle Ozone depletion Greenhouse effect Global Warming Pollution in the troposphere 1
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Mary J. Bojan Chem 110 Gases and the atmosphere Review Composition of the atmosphere Use mole fraction and ppm Pressure profile of atmosphere Low pressure means few molecular collisions Chemical reactions occur less frequently Temperature profile of atmosphere High temperature means avg. KE of molecules is high! 2
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Mary J. Bojan Chem 110 Composition of the atmosphere mole fraction: N 2 and O 2 represent > 99% of atm 3 x i = moles of i total moles
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Mary J. Bojan Chem 110 Composition of the atmosphere Eg. Neon x Ne = 0.00001818 Ne concentration = 18.18 ppm For other components use parts per million (ppm). ppm = x i ! 10 6 4 If you know the barometric pressure, you can determine the partial pressure. P BAR = 0.987 atm= P TOT P Ne = x Ne P TOT = 18.18 ! 10 -6 ( 0.987 atm) = 17.94 ! 10 -6 atm
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Mary J. Bojan Chem 110 Pressure decreases exponentially with altitude. WHY? What is pressure? 5 Pressure at any altitude depends on weight of gas above it.
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Mary J. Bojan Chem 110 Pressure and altitude Altitude P collision frequency (km) (atm) (sec -1 ) 0 1 10 10 50 10 -3 10 7 100 10 -6 10 3 200 10 -13 1 6 • Low pressure means fewer collisions • When collision frequency is low, chemical reactions occur less frequently
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Mary J. Bojan Chem 110 Based on Temperature Profile Thermosphere:
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11_Chapt18_1 - Gases and the atmosphere Chemical reactions...

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