Absorption and Henry's Law: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • Henry’s law is used when a gas above its critical temperature absorbs in a liquid.
  • The amount of gas dissolved at low concentrations is linear in pressure.
  • A higher Henry’s constant (as defined in this module) corresponds to a lower concentration in the liquid phase because it means the component has a higher fugacity.
  • Henry’s constant is defined in different ways in the literature so that when component A has a higher Henry’s constant than component B, then A could have a lower or higher solubility, depending on the definition. For this module, a higher Henry’s constant corresponds to a lower solubility.
  • For many gases, the amount of gas absorbed decreases as temperature increases at room temperature. For aqueous solutions, the amount of gas adsorbed goes through a minimum above room temperature (the minimum temperature depends on the gas).
  • The amount of gas adsorbed at a given temperature for different gases can differ by more than two orders of magnitude.
  • The Henry’s constant depends on temperature and the solvent.
  • Note that gases also absorb in solids, such as gas absorption in polymers.
From studying this module, you should now be able to:
  • Given the pressure of a gas and its Henry’s constant, calculate the mole fraction of a gas absorbed in a liquid.
  • Explain how the amount of gas adsorbed depends on temperature and pressure.


Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder