Gas Mixtures

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Gas Mixtures

• Chapter 13

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Composition of a Gas Mixture Mass and Mole
Fractions

• Mass Fraction (mf) The ratio of mass of a
  component to the mass of the mixture is called
  the mass fraction.
• Mole Fraction (y) The ratio of the mole number
  of a component to the mole number of the mixture
  is called the mole fraction.

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• The mass of a substance can be expressed in terms
  of the mole number N and molar mass M of the
  substance as
• The molar mass and the Gas constant of a mixture
  can be expressed as

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P-v-T Behavior of Gas Mixtures

• Is based on
• Daltons Law of additive Pressures
• Amagats Law of additive Volumes

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Daltons Law of additive Pressures

• The pressure of a gas mixture is equal to the sum
  of the pressures each gas would exert if it
  existed alone at the mixture temperature and
  volume

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Amagats Law of additive Volume

• The volume of a gas mixture is equal to the sum
  of the volume each gas would occupy if it existed
  alone at the mixture temperature and pressure

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P-v-T Behavior of Ideal Gas Mixtures

• For ideal gases ,the above two laws are identical
  and give identical results.
• Pi is called the component pressure and Vi the
  component volume.
• The ratio Pi/Pm is called the pressure fraction
  and the ratio Vi/Vm is called the volume fraction
  of component i.

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• Ideal Gas Mixtures
• Partial Pressure The quantity yiPm is called the
  partial pressure
• Partial Volume The quantity yiVm is called the
  partial volume
• For ideal gas mixture, the mole fraction, the
  pressure fraction and the volume fraction of a
  component are identical

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Real Gas Mixtures

• For real gases Daltons Law of additive Pressures
  and Amagats Law of additive Volumes can be used
  with reasonable accuracy.
• The components pressures and volumes need to be
  evaluated using more exact equations of state.
• Other ways is to use
• Compressibility factors
• Kays Rule

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Properties of Gas Mixtures

• The extensive properties of a gas mixture, can be
  determined by summing the contributions of each
  component of the mixture.
• The intensive properties of a gas mixture,
  involve averaging in terms of mass or mole
  fractions.

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Properties of Gas Mixtures

• SEE EXAMPLES 12.3-12.5 (TEXT)

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