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Chemistry LibreTexts

2: Adsorption of Molecules on Surfaces

  • Page ID
    25349
    • 2.1: Introduction to Molecular Adsorption
      The adsorption of molecules on to a surface is a necessary prerequisite to any surface mediated chemical process.
    • 2.2: How do Molecules Bond to Surfaces?
      There are two principal modes of adsorption of molecules on surfaces: Physical Adsorption (physisorption ) and Chemical Adsorption (chemisorption). The basis of distinction is the nature of the bonding between the molecule and the surface.
    • 2.3: Kinetics of Adsorption
      The rate of adsorption of a molecule onto a surface can be expressed in the same manner as any kinetic process.  For example, when it is expressed in terms of the partial pressure of the molecule in the gas phase above the surface.
    • 2.4: PE Curves & Energetics of Adsorption
      In this section we will consider both the energetics of adsorption and factors which influence the kinetics of adsorption by looking at the "potential energy diagram/curve" for the adsorption process.  The potential energy curve for the adsorption process is a representation of the variation of the energy (PE or E ) of the system as a function of the distance (d) of an adsorbate from a surface.
    • 2.5: Adsorbate Geometries & Structures
      We can address the question of what happens when a molecule becomes adsorbed onto a surface at two levels; specifically we can aim to identify (1) the nature of the adsorbed species and its local adsorption geometry (i.e., its chemical structure and co-ordination to adjacent substrate atoms) and (2) the overall structure of the extended adsorbate/substrate interface (i.e., the long range ordering of the surface) .
    • 2.6: The Desorption Process
      An adsorbed species present on a surface at low temperatures may remain almost indefinitely in that state. As the temperature of the substrate is increased, however, there will come a point at which the thermal energy of the adsorbed species is such that one of several things may occur. Including that  the species may desorb from the surface and return into the gas phase.  This the desorption process.

    Contributors

    • Roger Nix (Queen Mary, University of London)