GasChallenge_KEY_091008

GasChallenge_KEY_091008 - Gas Challenge Problems...

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Gas Challenge Problems Chem 1A F07 09/12-18/07 The van der Waals equation provides corrections for the assumptions made by the ideal gas law in order to apply to real gases. Data for common gases can be found in table 1. nRT nb V V an P ) )( ( 2 2 P = measuredPressure real gas V = measured Volume real gas n = moles real gas R = 0.082057 L atm mol -1 K -1 a = van der Waals pressure constant b = van der Waals volume constant Table 1: Common Gas Data (Note to GSI’s: Have students assume 1 bar = 1 atm) Gas Name Gas Formula a (L 2 bar/mol 2 ) b (L/mol) BP (degree C) MM (g/mol) ammonia NH 3 4.225 0.03707 -33.34 17.031 argon Ar 1.363 0.03219 -185.85 39.948 carbon dioxide CO 2 3.64 0.04267 -78.50 44.009 carbon monoxide CO 1.505 0.03985 -191.50 28.010 helium He 0.03457 0.02370 -268.93 4.003 hydrogen H 2 0.2476 0.02661 -252.87 2.016 methane CH 4 2.283 0.04278 -182.60 16.043 neon Ne 0.2135 0.01709 -246.08 20.180 nitrogen N 2 1.408 0.03913 -195.79 28.014 oxygen O 2 1.378 0.03183 -182.95 31.998 water H 2 O 5.536 0.03049 100.00 18.015 Boiling Point vs. Molar Mass NH 3 Ar CO 2 He H 2 Ne CH 4 N 2 O2 H 2 O y = 1.7508x - 195.89 R 2 = 0.0446 -300 -250 -200 -150 -100 -50 0 50 100 150 0 5 10 15 20 25 30 35 40 45 Molar Mass (g/mol) Temperature (degree C) Boiling Point vs. a constant 3 2 H 2 4 N 2 O 2 H 2 O y = 60.729x - 276.76 R 2 = 0.9593 -250 -100 -50 0 100 0 1 2 3 4 5 6 van der Waals a constant Temperature (degrees C)
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Gas Challenge Problems Chem 1A F07 09/12-18/07 Challenge Problems: 1) What two big assumptions are made when we use the ideal gas law equation: PV = nRT? Assumption 1: We assume that there is no interaction (attraction/repulsion) between gas particles, and consequently that gas particles collide elastically. Assumption 2: We assume that the volume of the individual gas particles is insignificant and that they take up no space. a. What does the a constant adjust for? Why is the pressure of a real gas usually smaller than that of an ideal gas? The a constant adjusts for the assumption that there is no interaction. Real gas particles do have intermolecular attractions (i.e. London dispersion, induced dipole, dipole-dipole, H-bonding) that are accounted for with the a constant.
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GasChallenge_KEY_091008 - Gas Challenge Problems...

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