chapter 5a - CHAPTER 5a The Properties of Gases 1 The...

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1 CHAPTER 5a The Properties of Gases 2 The Nature of Gases ± The fact that gases are readily compressed and immediately fill the space available to them suggest the molecules of gases are: ² widely separated ² in ceaseless chaotic motion 3 These are the eleven elements that are in the gas state during normal conditions. The following gases are diatomic in their standard state. H 2 N 2 O 2 F 2 Cl 2
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4 Comparison of Solids, Liquids, and Gases ± The density of gases is much less than that of solids or liquids . 0.00503 1.59 1.70 CCl 4 0.000588 0.998 0.917 H 2 O Gas Liquid Solid Densities (g/mL) 5 Composition of the Atmosphere and Some Common Properties of Gases 0.00005 H 2 0.00015 CH 4 0.002 He, Ne, Kr, Xe 0.03 CO 2 0.93 Ar 20.94 O 2 78.09 N 2 % by Volume Gas Composition of Dry Air 6 Pressure The collisions of gas molecules with the walls of the container give rise to the pressure exerted by gases. The large number of collisions exerts an almost steady force on the walls of the container.
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7 Pressure ± Pressure is force per unit area. ± Gas pressure as most people think of it. ² lb/in 2 ² N/m 2 ± The SI unit of pressure is the Pascal. F P A = 8 Atmospheric pressure is measured using a barometer. { The Hg in the tube falls until the pressure from the mass of the Hg in the tube is balanced by the pressure of the atmosphere on the mercury in the dish. { The pressure of the atmosphere is then expressed by the height of the Hg in the tube. 9 Figure 5.2: A simple manometer, a device for measuring the pressure of a gas in a container. ( ) gas atm PPh where difference in mercury lev s h el =− = ( ) gas atm where difference in mercury lev s h el =+ = (a) The gas pressure is lower than atmospheric pressure. (b) The gas pressure is greater than atmospheric pressure. ( ) gas atm where difference in mercury lev s h el =
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10 11 Pressure ± Definitions of standard pressure ² 76 cm Hg ² 760 mm Hg ² 760 torr ² 1 atmosphere ² 101.3 kPa 12 Pressure Because mercury barometers are very common: ² gas pressure is often expressed in mmHg ² gas pressure is also expressed in torr 1 mmHg = 1 torr ² atmospheric pressure decreases with increasing elevation (less mass of air)
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13 Pressure At 0 o C (273 K), 1.0 atm = 760 mmHg = 760 torr The SI unit is the pascal (Pa): 1.0 atm = 1.013 x 10 5 Pa = 101.3 kPa Learn these units of pressure!!! 14 Boyle’s Law: The Volume-Pressure Relationship Boyle’s Law : The effect of pressure on volume of gas. ± At constant temperature and with a constant number of moles gas: PV = k Where: ± P = pressure ± V = volume ± k = a constant at a specific temperature (determined experimentally) 15 Boyle’s Law: The Volume-Pressure Relationship The J-tube Hg poured into J-tube traps air at the closed end of the tube. a) Less Hg decreased pressure on trapped air and increased the volume the air occupied. b) More Hg increased pressure on trapped air and decreased the volume the air occupied.
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16 Boyle’s Law: The Volume-Pressure Relationship 17 Boyle’s Law: The Volume-Pressure Relationship Inverse relationship between pressure and volume.
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chapter 5a - CHAPTER 5a The Properties of Gases 1 The...

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