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Chapter 5

# Chapter 5 - 1 THE GASEOUS STATE Kinetic Theory of Gases an...

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1 THE GASEOUS STATE Kinetic Theory of Gases – an excellent model of gases 1. Gas molecules have negligible volume compared with space between molecules. - molecules are spread out 2. Gas molecules move. When they hit side of container they contribute to pressure. 3. All collisions are elastic . - molecules behave like billiard balls, not soggy softballs 4. Gas molecules have no attraction or repulsion for each other. - gas molecules don’t know other molecules are around 5. The speed of the gas molecules is proportional to the temperature. - kinetic energy of gas is related to speed Kinetic theory of gases is able to explain many properties of gases. 1. Gases are compressible . 2. Gases have low densities. Gases mix completely. Gases fill container uniformly. Gases exert pressure on side of container. Kinetic theory explains diffusion of gases very well. - Diffusion is the travel of gases through space so that they mix completely. - Gasoline molecules from open gas can diffuse through room. PRESSURE Definition Pr essure Force Area = A square meter column of air weights 101,325 N. - 22,730 lbs. Atmospheric essure N m N m Pr = = 101325 1 101325 2 2 SI Unit of pressure is Pascal – Pa 1 1 2 Pa N m = Atmo ess N m Pa kPa . Pr . . = = = 101325 2 Pressure is measured with a barometer . - Pressure of mercury column on surface of Hg pool balances atmospheric pressure pushing on Hg pool. - Height of column indicates atmospheric pressure. - At sea level, column of Hg is 760 mm (29.92 in.) - At sea level, column of H 2 O is 33.7 ft!! (see exhibit of atrium of DSC) atmospheric pressure pressure of Hg column vacuum (no air) Hg pool

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2 UNITS OF PRESSURE 1.) Pascals (Pa) 2.) Atmospheres (atm) 3.) Torr or mmHg Must be able to convert between atmospheres and Torr (mmHg). 1 760 760 atm Torr mmHg = = Example: How many mmHg is 0.858 atm? - aside: Lowest pressure of Typhoon Tip (1979) How many atmospheres is 3.8 x 10 8 Torr? - aside: Pressure at the center of the earth BOYLE’S LAW Pressure and volume of a gas are inversely proportional to each other, all other factors being constant (such as temperature and amount). P V 1 P k V PV k = = = P V P V 1 1 2 2 Consider cylinder with piston P a P a Now apply additional external pressure, P ex . - I.e., push down on piston.
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Chapter 5 - 1 THE GASEOUS STATE Kinetic Theory of Gases an...

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