Adsorption: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • Higher temperatures result in lower adsorption coverages for a given pressure.
  • An adsorption isotherm is a plot of amount adsorbed (or fraction of the amount adsorption) versus gas-phase pressure at equilibrium at one temperature.
  • Molecules with higher heats of adsorption have higher surface coverages.
  • At sufficiently low pressures for adsorption that obey a Langmuir isotherm, surface coverage is linearly proportional to pressure.
  • At sufficiently high pressures, surfaces become saturated so that increasing the pressure does not increase the surface coverage.
  • Langmuir isotherms assume all sites on a surface are uniform.
  • At adsorption equilibrium, the rates of adsorption and desorption are equal.
  • The adsorbent is the solid on which an adsorbate adsorbs.
From studying this module, you should now be able to:
  • Know the meanings of adsorption, adsorbent, and adsorbate.
  • Calculate the amount of adsorbent needed to decrease the amount of adsorbate in the gas phase to a fraction of its initial value, given constants for a Langmuir isotherm at the temperature of interest.
  • Given at least two measurements for the amount adsorbed and its equilibrium pressure, determine Langmuir isotherm parameters.
  • Given adsorption measurements (amount adsorbed and equilibrium pressure) at two or more temperatures, determine the heat of adsorption.

See also: Langmuir-Hinshelwood Kinetics

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