Simple Mixtures Continued

1
Simple Mixtures Continued
2
Gibbs Energy of Mixing of Perfect Gases

• Recall, mmolar Gibbs Energy

3
Entropy and Enthalpy of Mixing

• Mole fractions are always lt0. Therefore, DSMIX
  is always gt0.
• Since there is no interaction between molecules
  in a perfect gas, DHMIX0.

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Note the form of the Curves
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Problem 7.13b
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Chemical Potentials of Ideal Solutions

• When A(l) is in equilibrium with A(g) at a
  partial pressure PA, then
• Recall, mA for a vapor is
• Therefore, at equilibrium

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Chemical Potentials of Ideal Solutions

• Raoults Law
• Measured the partial vapor pressure of each
  component in a mixture
• Discovered that the partial pressure of the
  solvent of a solution was lower than the pressure
  of the pure solvent

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Chemical Potentials of Ideal Solutions

• Using Raoults Law, substitute for PA

Constants for a given substance at a given
temperature
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Problem 7.9b
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Ideal Binary Solutions

• Raoults Law applies to each component (A and B)
• The total pressure of the system follows Daltons
  Law

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Ideal-Dilute Solutions

• A solute lowers the chemical potential of a
  solvent
• increases the disorder of the solvent
• The disorder of a solvent of a solution is higher
  but it has a lower tendency to achieve disorder
  than the pure solvent.
• this reduction in potential is m lower than m.

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Ideal-Dilute Solutions

• Raoults Law describes properties of an almost
  pure solvent in a real solution.
• Raoults Law does not work well in describing the
  partial vapor pressure of the solute.
• Since it its the minor component, the solute is
  far from its pure state
• However, it is known that the partial vapor
  pressure of the solute is proportional to the
  mole fraction of the solute.
• The slope of this line is different that what
  Raoults Law describes

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Henrys Law

• The vapor pressure of a volatile solute (b), is
  equal to its mole fraction in solution times a
  constant characteristic of the solute
• KB is the pressure at xB1 determined by a line
  that is tangential to the point at xB0

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Limitations
Limitations

• Raoults and Henrys Laws are valid only at low
  concentrations of solute and solvent,
  respectively.

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Problem

• Estimate Henrys Law constant for methylene
  chloride given the following data

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Problem 7.15b(a)