401gases - Gases Glenn V. Lo Department of Physical...

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    Gases Glenn V. Lo Department of Physical Sciences Nicholls State University
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    Describing a gas Ideal gas equation: PV = nRT Valid as P 0; ordinary conditions (about  1% error) P = pressure V = volume n = number of moles R = a constant T = temperature in Kelvin
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    Pressure Measurement Traditional measurement:  use a column of mercury Barometric pressure =  height of Hg supported by  atmosphere At sea level:   1 atm = 760 mm Hg
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    Pressure Measurement Closed-end manometer P gas  = h
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    Pressure Measurement Open-end manometer P gas  = P bar  + h P gas  = P bar  - h
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    Pressure: Units Pressure = force per unit area SI Unit: 1 Pa = 1 N m -2 Traditional units: atmosphere, Torr 1 atm = 760 Torr = 1.01x10 5  Pa Newer units: 1 bar = 1000 mbar = 10 5  Pa “Standard Pressure” Current definition: 1 bar Gen. Chem textbooks: 1 atm ( 1.01 bar)
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    Units of R PV = nRT    R = PV/RT Value of R depends on units used for  P, V, R, T.  R = 0.08205 L atm mol -1  K -1 R = 0.08314 L bar mol -1  K -1 R = 8.314 J mol -1  K -1 Note: 1 Joule = 1 J = 1 N m = 1 Pa m 3 MUST use Kelvin temperature
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    Counting molecules in a gas STP = standard temperature and  pressure; 0 o C, 1 atm A 22.4 L sample of He at STP  contains how many molecules? n = PV/RT
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  Counting molecules in a gas SATP = standard ambient  temperature and pressure; 25 o C, 1  bar A 24.8 L sample of He at SATP  contains how many molecules? n = PV/RT = ?
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401gases - Gases Glenn V. Lo Department of Physical...

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