Chapter5 - Chapter 5: Gases Laws for gases are simpler than...

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Chapter 5: Gases Laws for gases are simpler than for liquids and solids. The behavior of gases is predictable. 5.1 Substances that exist as gases Air - 78 % N 2 ; 21 % O 2 ; 1 % other (including CO 2 which is associated with global warming) A. Elements and Molecules O 2 , H 2 , N 2 , F 2 , O 3 , all Group VIII (Noble gases) Ionic compounds are never gases at room temperature (24 ° C at 1 atmosphere); electrostatic forces are too strong to allow ions to separate molecular compounds that are small can be gases or have low boiling points: CO, CO 2 , HCl, CH 4 , NH 3 , SO 2 , etc. B. Characteristics of Gases assume volume and shape of container very compressible mix evenly and completely lower density than liquids and solids 5.2 Pressure of a Gas Molecules of a gas are in rapid and constant motion. A. Units of Pressure SI Units force = mass x acceleration Newton (N) = Kg x m/s 2 Pressure = force/area = 1 N/ m 2 = Pascal (Pa)
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Chapter 5 Chemistry 1303 2 B. Atmospheric Pressure pressure exerted by Earth's atmosphere gas molecules have mass, thus gravity affects them 50 % of the atmosphere's molecules are within 4 miles of surface measured by barometer (Figure 5.3) 760 mm Hg at sea level standard is 1 atm at 0 ° C 1 atm = 1.01325 x 10 5 Pa 1 mm Hg = 1 Torr 1 atm = 760 Torr = 760 mm Hg 5.3 Gas Laws 3 simple laws : Boyle's, Charles', Avogadro's A. Boyle's Law (at constant T and n) volume decreases as pressure increases V 1/P or PV = constant P 1 V 1 = P 2 V 2 See Figure 5.6 B. Charles' Law (Gay-Lussac's) (at constant P and n) volume increases as temperature increases V T or V / T = constant V 1 /V 2 = T 1 /T 2 always use the Kelvin Scale for T Figure 5.9 note all lines converge at absolute 0 or -273.15 ° C 0 K = -273.15 ° C
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Chapter 5 Chemistry 1303 3 C. Combined Gas Law (for constant n) PV / T = constant D. Avogadro's Law (constant temperature and pressure) equal volumes of gas have the same number of molecules (atoms)
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This note was uploaded on 08/22/2011 for the course CHEM 101 taught by Professor C during the Spring '11 term at University of Texas at Dallas, Richardson.

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Chapter5 - Chapter 5: Gases Laws for gases are simpler than...

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