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Phases of Matter Properties of a Gas Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology
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Properties of Gases Reading Assignment: Zumdahl, Chapter 5.1-5.3 This lecture introduces the interrelated dependence of moles, temperature, pressure and volume of a confined gas. Based on assumptions of ideal gas behavior, these parameters when combined form the ideal gas equation, PV=nRT.
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Phases of Matter Gases Liquids Solids Plasma
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Gases Large intermolecular distances, compared to molecular size No long or short range structural order
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Gases Mix together in any proportions Intermolecular collisions are elastic -- energy is transferred through collisions
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Liquids Small intermolecular distances -- molecules are "touching" Molecules may be ordered with respect to each other over a short range, but no long range structural order Energy is transferred through molecular vibration
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Liquids May or may not be miscible
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Liquids Aqueous solutions are like liquids, except solute is surrounded by solvent
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Solids Small intermolecular distances -- molecules are "touching" Long and short range structural order in crystalline solids Energy is transferred through molecular vibration
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Solids Amorphous solids have less structural order
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Solids Very limited miscibility while remaining in the solid state
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Solids Frozen solutions are possible and called solid solutions
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Plasma High energy state in which all molecules are broken into constituent atoms, and most or all of the electrons are stripped from the atom Very high temperature ( 10 6 K), condensed, gas-like phase consisting of nuclei and electrons
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Plasma Nuclei mix together in any proportions Applications occur in a few analytical detection techniques and nuclear reactions Not involved in typical chemical reactions
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Physical Properties of Matter Temperature Pressure Volume Moles
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Temperature Temperature is a measure of molecular motion: vibration, rotation and translation Gases move at high velocity (> 1000 m·sec –1 ) Common units: Celsius (°C), Fahrenheit (°F)
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Temperature Absolute units: Kelvin (K), Rankine (°R) 0.00 °C = 273.15 K = 32.00 °F = 491.67 °R 100.00 °C = 373.15 K = 212.00 °F = 671.67 °R Isothermal - constant temperature
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Pressure Due to molecules hitting the surface Force per unit area
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Pressure What do you know about the pressure in a balloon?
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Pressure Within a closed container with a flexible or moveable barrier, the external forces pushing on the surface of the container containing the gas are equal to the pressure of the trapped gas pushing out.
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Barometer mercury vacuum What forces determine the height of the mercury in the glass tube?
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atmospheric pressure What forces determine the height of the mercury in the glass tube? Barometer
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760 mm 30 in How much pressure does the atmosphere exert? Hg = 13.6 g· cm –3 = 0.490 lb·in –3 1.03 kg· cm –2 = 14.7 lb· in –2
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Barometer H 2 O= 1.0 g· cm –3 33 feet What is different if water is used as the fluid, rather than mercury?
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Pressure Common units: lbs·in –2, atmospheres (atm), mm Hg, torr, pascals (N·m –2, Pa) 1.00 atm = 14.7 lbs·in –2 = 760 mm Hg = 760 torr = 1.013 x10 5 Pa
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Pressure The actual atmospheric pressure is a function of the weather (high or low pressure) and altitude. Typical Terre Haute pressure is 730-750 mm Hg. Isobaric - constant pressure
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Volume Gases occupy the complete volume to which they are constrained Liquids and solids occupy a volume corresponding to their mass and density Isochoric - constant volume
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Moles A counting unit for the number of molecules being considered
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Physical Laws of Gases Boyle's Law Charles' Law Avogadro's Law Ideal Gas Law
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Boyle's Law P·V = constant isothermal constant amount of gas volume pressure What does a plot of this relationship look like?
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Charles' Law VTVT isobaric constant amount of gas volume temperature What does a plot of this relationship look like? What does the y-intercept indicate?
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Avogadro's Law VnVn isobaric isothermal volume moles of gas What does a plot of this relationship look like?
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Gas Laws volume pressure Boyle volume temperature Charles volume moles of gas Avogadro V 1/PV TV n V nT P
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Ideal Gas Law P·V n·T PV = nRT where R = ideal gas constant = 0.08206 L·atm·mol –1 ·K –1
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Boyle's Law P·V = constant isothermal constant amount of gas volume pressure How will this plot change if the same number of moles of gas are at a higher temperature?
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Common Gases Room Temperature, One Atmosphere Pressure Monatomic: He, Ne, Ar, Kr, Xe, Rn Polyatomic Elements: N 2, O 2, O 3, F 2, Cl 2 Compounds: CO, CO 2, NO, N 2 O, NO 2, N 2 O 4, N 2 O 5, CH 4, C 2 H 6, C 2 F 4, etc.
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Atmospheric Composition Dry air 78% N 2, 21% O 2, 1%Ar Normal air N 2, O 2, Ar, 0.03% CO 2, 1.6% H 2 O
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