Chapter10.2008.forBB

Chapter10.2008.forBB - Chemistry: The Molecular Science...

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Chapter 10: Gases and the Atmosphere Chemistry: The Molecular Science Chemistry: The Molecular Science Moore, Stanitski and Jurs Gas % by vol Nitrogen 78.084 Oxygen 20.948 Argon 0.934 Carbon dioxide 0.031 1 ppm 100 ppb 80 ppb 20 ppb 10 ppb 1ppb 200 ppt Gas % by vol Krypton 0.0001 Carbon monoxide 0.00001 Xenon 0.000008 Ozone 0.000002 Ammonia 0.000001 Nitrogen dioxide 0.0000001 Sulfur dioxide 0.00000002 Neon 0.00182 Hydrogen 0.0010 Helium 0.00052 Methane 0.0002 Dry air at sea level 99.997% Other units: parts per million (ppm) parts per billion (ppb) by volume by volume parts per trillion (ppt) 1% = 10,000 ppm = 10,000,000 ppb The Atmosphere
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The Troposphere and Stratosphere • The atmosphere is divided (by T variation) into layers. • 75% of the mass and “weather” occur in the troposphere. 99.9% of the mass is in the 2 lowest layers. 170 190 210 230 250 270 290 Temperature (K) Altitude (km) 0 10 20 30 40 50 60 70 80 90 100 110 troposphere stratosphere mesosphere thermosphere mesopause stratopause tropopause 0 200 400 600 800 Pressure (torr) Gas Formula Typical Use Acetylene (ethyne) C 2 H 2 Welding torch fuel Ammonia NH 3 Fertilizer Argon Ar Filling for light bulbs Butane C 4 H 10 Fuel for space heating (LP gas) Carbon dioxide CO 2 Carbonation of beverages Chlorine C l 2 Disinfectant, bleach Ethylene (ethene) C 2 H 4 Polymer manufacturing (polyethylene) Helium He Lighter-than-air aircraft Hydrogen H 2 Hydrogenation of oils; possible fuel of the future Methane CH 4 Fuel (natural gas) Nitrous oxide N 2 O Anesthetic Propane C 3 H 8 Fuel for space heating (LP gas) Sulfur dioxide SO 2 Preservative, disinfectant Properties of Gases Table 10.2 Some Common Gases and Their Uses
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Properties of Gases can be compressed exert pressure on whatever surrounds them expand into whatever volume is available easily diffuse into one another can be described in terms of their temperatures and pressure,the volume occupied, and the amount (number of molecules or moles) present Properties of Gases Gases can be compressed Gases can be compressed • Liquids and solids are extremely hard to compress.
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Properties of Gases Gases expand into any available volume • gas molecules escape from open containers. Gases are completely miscible Gases are completely miscible • once mixed they will not spontaneously separate. Gases are described in terms of T, P, V T, P, V and and n • more later… Gas Pressure
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Press ure pressure = force/area Averaged over many collisions! Pressure = = Force mass x acceleration Area Area Force is exerted when gas molecules strike container walls. Pressure Units SI: 1 pascal (Pa) = 1 kg m -1 s -2 = 1N m -2 others: 1 bar = 10 5 Pa = 100 kPa 1 atm = 101.325 kPa = 1.01325 bar 1 atm = 760 torr = 760 mm Hg 1 atm = 14.7 lb/in 2 Gases Exert Pressure
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Pressure can be measured with a barometer: barometer: gravity g = 9.81 ms -2 P = m x acceleration area = m x g x height volume = density x g x h = d g h Gases Exert Pressure Atmospheric Pressure Calculate the pressure (in atm) exerted by a 34-foot tall column of water. Assume d water = 0.998 g cm -3
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Chapter10.2008.forBB - Chemistry: The Molecular Science...

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