Chapter 22 Summary

Summary

The Properties of Gases in Gas Mixtures and Aqueous Solutions

  • The total pressure of a gas mixture is the sum of the partial pressures exerted by the individual gases in the mixture. The partial pressure of each gas is independent of the other gases present.
  • In gas mixtures, the concentration and the partial pressure of any given gas are simply proportional to each other. The proportionality coefficient is the same for all gases, at any given temperature, because it is a corollary of the universal gas law.
  • When gases dissolve in aqueous solutions, they disappear into solution, just as sugars disappear when they dissolve. Bubbles of gas, no matter how tiny, are not in solution.
  • The partial pressure of a gas dissolved in an aqueous solution is equal to the partial pressure of the same gas in a gas phase with which the solution is at equilibrium.
  • In an aqueous solution, the concentration and the partial pressure of any given dissolved gas are proportional. However, the coefficient of proportionality, termed the absorption coefficient, varies greatly from gas to gas, and depends on temperature and salinity.
  • Gas solubility decreases with increasing temperature and also with increasing salinity.

Diffusion of Gases

  • Gases always diffuse from regions of high partial pressure to regions of low partial pressure and at a rate that is proportional to the difference in partial pressure. A gas is at equilibrium in a system when its partial pressure is uniform throughout.
  • Diffusion occurs much more readily through air than water. Specifically, the Krogh diffusion coefficient is 200,000 times greater for O2 and 9000 times greater for CO2 in air than in water (at 20ÂșC).
  • When gas molecules undergo chemical combination, they cease to contribute to the partial pressure of the gas in question and thus no longer affect the direction or rate of diffusion of the gas.
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