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Ch 5 Gases Review

Ch 5 Gases Review. AP Chemistry 2014-2015. General Things to know. 1 atm = 760.00 mmHg = 760.00 torr = 101.325 kPa = 1.013 x 10 3 Pa = standard pressure (sea level) STP = 273 K, 1 atm R = 0.08206 Latm / molK or 8.314510 J/ molK.

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Ch 5 Gases Review

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  1. Ch 5 Gases Review AP Chemistry 2014-2015

  2. General Things to know • 1 atm = 760.00 mmHg = 760.00 torr = 101.325 kPa = 1.013 x 103 Pa = standard pressure (sea level) • STP = 273 K, 1 atm • R = 0.08206 Latm/molK or 8.314510 J/molK

  3. Combined gas law use to get boyle’s, Ga-Lussac’s, Charles’s Laws • P1V1/T1= P2V2/T2 •  memorize it (“peas and vegetables on the table”)

  4. 5.3 The Ideal Gas Law • PV = nRT • R = 0.08206 Latm/molK, though it has other values and units as well; useful only at low pressures and high temperatures

  5. The Density of Gases • “Molecular Mass kitty cat”—all good cats put dirt (dRT) over their pee (P). Ew, but it works. • Remember that the densities of gases are reported in g/L not g/mL.

  6. Dalton’s Law of Partial Pressures • Ptotal = P1 + P2 + …. + Pn • You can also use this concept when collecting a gas over water; total pressure = atmospheric pressure • Ptotal = Pgas + Pwater

  7. The Kinetic Molecular Theory of Gases • Assumptions • All particles are in constant, random motion • All collisions between particles are perfectly elastic • The volume of the particles in a gas is negligible • The average kinetic energy of the molecules in a gas it is its Kelvin temperature • These assumptions ignore intermolecular forces. • IMFs are stronger for larger/polar particles, weaker for smaller/nonpolar particles

  8. Distribution of molecular speeds • Follows a rough bell curve • At any temperature, some particle will have zero (or near-zero) velocity • As temperature increases, the curve shifts to the right and flattens • Average kinetic energy is only tied to temperature; velocity is tied to both temperature and molar mass

  9. Root Mean Speed • Urms = root mean speed, m/s • T = temperature, Kelvin • MM = mass of a mole of gas particles in kg (weird, I know—respect the math though) • Use the “energy R” or 8.314510 J/molK for this equation since kinetic energy is involved.

  10. Comparing rates of effusion for gases with different molar masses • Make sure to keep track of which gas is “gas 1” and which gas is “gas 2” to keep from messing up • Low molar mass = faster effusion, high molar mass = slower effusion

  11. Ideal vs. Real Gases • Real gases behave most ideally • At high temperature • At low pressure • When they have weaker IMF’s (smaller, nonpolar molecules) • The van der Waal’s equation has terms that correct for • Volume of gas particles (term “b”) • IMF’s between gas particles (term “a”)

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