Surface Chemistry
Surface Chemistry
Surface Chemistry
…………(equ 1)
Adsorption Isotherm
Taking the logarithms of equ 1:
…………… (equ 2)
The validity of Freundlich isotherm can be verified by plotting log x on y-axis (ordinate)
m
and log p on x-axis (abscissa).
NOTE: If it comes to be a straight line, the Freundlich isotherm is valid,
otherwise not.
• The slope of the straight line gives the value of 1
n
Freundlich Isotherm
• The following observations have been made in the case of adsorption from
solution phase:
❖ The extent of adsorption decreases with an increase in temperature.
❖ The extent of adsorption increases with an increase of surface area
of the adsorbent.
❖ The extent of adsorption depends on the concentration of the solute
in solution.
❖ The extent of adsorption depends on the nature of the adsorbent
and the adsorbate.
NOTE: The precise mechanism of adsorption from solution is not known.
Adsorption from solution phase (contd.)
• Plotting log x against log C a straight line is obtained which shows the
m
validity of Freundlich isotherm.
APPLICATION OF ADSORPTION
• Catalyzed destruction of
ozone by Cl in the upper
atmosphere.
Promoters and Poisons
• Promoters are substances that enhance the activity of a catalyst while
poisons decrease the activity of a catalyst.
• For example, in Haber’s process for manufacture of ammonia,
molybdenum acts as a promoter for iron which is used as a catalyst.
Homogeneous and Heterogeneous Catalysis