chem161sg_chapter5

chem161sg_chapter5 - CHAPTER 5 GASES States of Matter A....

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CHAPTER 5 GASES States of Matter A. Condensed Phases B. Gaseous Phases The state at which a certain substance exists, depends on its temperature and pressure. heat heat Solid Ice Liquid H 2 O Gaseous H 2 O - ordered state - less ordered than solid - no order - strong attraction - less attraction - random motion between molecules between molecules - ideally molecules do not - fixed shape - takes the shape attract/repel each other of the container - expansible - very hard to compress - compressible Common properties of all gases 1. Expandability 2. Compressibility V (liquid) V (gas) 1 g O 2 0.894 mL (at –183 0 C) 700 mL (at 0 0 C) 1 g NH 3 1.54 mL 1390 mL 1 g solid CO 2 0.641 mL 1 g gaseous CO 2 at 0 0 C ~550 mL The physical laws that govern the behavior of the gases are the same irrespective what that gas is. Some of the characteristics of gases are pressure and volume (e.g. volume of air and its pressure in the tire.) 1
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Gases could be… monoatomic; He, Ar, Ne diatomic; N 2 , O 2 triatomic; O 3 (ozone), NO 2 , SO 2 polyatomic; CH 4 (methane), C 2 H 6 (ethane), etc. Air: a mixture of gases… % Gas ~ 7 8 N 2 ~ 2 1 O 2 ~ 1 A r ~ 0 . 0 3 C O 2 The Kinetic Theory of Gases: Introduction 1. The ideal gas is composed of small molecules that have mass but negligible volume . 2. Gas molecules are in constant motion.(Translational motion: moving through three dimensions) They do not exert neither attractive nor repulsive forces on each other.( Ideal behavior) 3. The collision of molecules with each other and the walls of the container are elastic i.e. the total translational kinetic energy (K.E.) remains constant. The average translational energy of a gas depends on its temperature only. Two gasesat the same temperature have the same average translational K.E. K.E. = mv 2 where… m = mass, v = velocity 1 2 2
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Gas Pressure One of the most important properties of gases is the pressure that it exerts on the walls of the container it is confined in. less gas more gas less pressure more pressure Pressure results from collisions of the gas molecules on the walls of the container . The greater the amount of gas ( n = number of moles ) the higher the pressure it exerts. force area Pressure is defined as… P = The SI unit for pressure is Pascal (Pa). 1Pa = 1N/m 2 ; N = Newton, unit of force. If the force (gravitational force = weight) is distributed over large surface , then the pressure is going to be less for the same force. The pressure inside the container depends on the amount of the gas present, on the volume of the container, and on the temperature of the gas. NOTE: Distinguish between “gas” and “vapor,” two terms used interchangeably but they do not have exactly the same meaning. “gas”:
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chem161sg_chapter5 - CHAPTER 5 GASES States of Matter A....

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