a) Physical adsorption or physisorption decreases with increase of temperature where as chemical adsorption increases with increase of temperature reaches a maximum value at an optimum temperature and then decreases with increase in temperature.
b) Physisorption of a gas adsorbed at low temperature may transform into chemisorption at a high temperature. This is due to the fact that no activation energy is required for physisorption while chemisorption requires activation energy. For example, dihydrogen is first adsorbed on nickel by van der Waals’ forces. This is physisorption. Molecules of dihydrogen then dissociate to form hydrogen atoms which are held on the surface by chemisorption.
c) When excess of a salt (electrolyte) is added, the colloidal particles interact with ions carrying charge opposite to that present on themselves. (According to Hardy-Schultz rule).
