Chapter 10 - CHEMISTRY The Molecular Science Chapter ten...

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CHEMISTRY The Molecular Science Chapter ten Gases and the Atmosphere
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The Atmosphere – exerts a pressure on the surface of the earth. – composed mainly of N 2 , O 2 and 13 minor gases.
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Due to the force of gravity, atmospheric molecules are concentrated near the earth’s surface. concentrations : % by volume ppm parts per million: 1 / 1 million ppb parts per billion: 1 / 1 billion 9.34 ppm Ar = 9.34 cm 3 Ar/ 1x10 6 cm 3 air
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Many molecular compounds are gases at RT and atmospheric pressure. Diatomics : O 2 , N 2 , H 2 , F 2 and Cl 2 .
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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 (or mix completely with) one another. can be described in terms of their temperatures and pressure, the volume occupied, and the amount (number of molecules or moles) present.
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Gases collide with the walls of their container – exert a pressure. Pressure = force / area Force = mass x acceleration. Newton (N) – unit of force (kg m /s 2 ). 1 N / m 2 = 1 pascal (Pa).
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Torricellian Barometer The earth’s atmosphere exerts a pressure on everything below it. At sea level Hg height = 760 mm Hg = 760 torr = 1 atm Any liquid can be used – the height of the column will depend on the density of the liquid inside.
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Practice Problem 10.1 p. 435 A TV weather person says the barometric pressure is “29.5 inches of mercury”. What is this pressure in a) atm b) mm Hg c) bar d) kPa 1 in = 25.4 mm
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Kinetic Molecular Theory: Gases The pressure a gas exerts on the walls of its container is due to the collisions with the container walls. A gas is composed of molecules whose size is much smaller than the distances between them. Gas molecules move randomly at various speed and in every possible direction. Except when gas molecules collide, forces of attraction between them are negligible.
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When collisions between molecules occur; they are elastic (total KE remains constant). The average kinetic energy of gas molecules is proportional to the absolute temperature. Kinetic energy : E k = ½mv 2 Gas molecules do not move at the same speed – there is a distribution of speeds. Speed of an individual molecule changes as it collides with
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Distribution of Molecular Speeds Maximum = most probable speed. Average speed is a little
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This note was uploaded on 10/03/2010 for the course CHE 131 taught by Professor Kerber during the Summer '08 term at SUNY Stony Brook.

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Chapter 10 - CHEMISTRY The Molecular Science Chapter ten...

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