Show by a graphic diagram how at a constant pressure a rise in temperature will influence adsorption of a gas on solid when (i) No compound formation occurs, (ii) Chemisorption takes place.

The process of Adsorption is an Exothermic Reaction. Thus according to Le-chatlier’s Principle, the magnitude of adsorption should increase with decrease in temperature. Infact it is found to be so in case of physical adsorption because vanderwaal’s forces are strong at low temperatures. However, the chemisorption first increases with rise in temperature and then starts decreasing. The initial increase shows that like chemical reactions, chemisorption also needs activation energy.



 If a plot is drawn between amount of gas adsorbed (x/m) and temperature at constant equilibrium pressure, then curve obtained for physical adsorption shows there is a regular decrease in adsorption with temperature rise. While for chemisorption it first increases and then shows regular decrease. Such curves are known as Adsorption Isobars.