Molar Mass Using Density

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Molar Mass Using Density

• Molar mass dRT
• P
• Example the density of a gas was measured at
  1.50 atm and 27ºC and found to be 1.95 g/L.
  Calculate the molar mass of the gas.
• Answer 32.0 g/mol

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Daltons Law of Partial Pressures

• The total pressure of a gas mixture is the sum of
  the partial pressures of the component gases.
• Ptotal P1P2P3P4
• For a mixture of ideal gases, the total number of
  moles of particles is important, not
  identity/composition

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Simple Example

• A gas mixture containing oxygen, nitrogen, and
  carbon dioxide has a total pressure of 32.9 kPa.
  If PO26.6 kPa and PN223.0 kPa, what is PCO2?
• COMPLEX EXAMPLE pg. 200 in book!

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Mole Fraction

• Ratio of moles of solute to total number of moles
  of solute(s) and solvent
• No unit necessary
• Watch out for significant figures

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Formula

• X1 or 2 mole fraction of solute 1 or 2
• 1 solute 1
• 2 solvent
• X1 n1 _
• n1 n2
• X2 n2 _
• n2 n1

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Example

• Calculate the mole fraction of each component in
  a solution of 42.0g CH3OH, 35.0g C2H5OH, and
  50.0g C3H7OH.
• Answers CH3OH 0.451, C2H5OH 0.262, C3H7OH
  0.287
• (should add up to make 1)

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Also

• Mole fraction also works with pressures

• X1 or 2 mole fraction of solute 1 or 2
• 1 solute 1
• 2 solvent
• X1 p1 _ X2 p2 _
• p1 p2 p2 p1

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Collecting Gas Over Water

• Vapor pressure
• Go over example pg. 204

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Kinetic Molecular Theory

• The volume of the individual particles can be
  assumed to be negligible (zero).
• Gases are mostly empty space.
• Gas particles are not attracted to each other.

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• 2. Gas particles are in constant motion. The
  collisions of the particles with the walls of the
  container are the cause of the pressure exerted
  by the gas.

• 3. The particles are assumed to exert no forces
  on each other they are assumed neither to
  attract nor to repel each other.
• Elastic means no loss of energy.
• Like two billiard balls hitting each other
  energy can be transferred but not lost.

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• 4. The average kinetic energy of a collection of
  gas particles is assumed to be directly
  proportional to the Kelvin temperature of the
  gas.
• Only explains properties of an ideal gas. A real
  gas does not conform to these
• We can relate each of the gas laws to the KMT.

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Average Kinetic Energy Calculation

• KEavg (3/2)RT
• R 8.3145 J/Kmol
• T KELVIN!
• Example Calculate the temperature of a mole of
  nitrogen molecules if the internal energy is 2.11
  X 104 J. Assume ideal gas behavior.
• Answer 1692K 1419ºC