Question

Why does physisorption change to chemisorption at high temperatures?

Answer 1

Dear student!  Chemiosorption is an endothermic process and involves high energy for activation because it occurs in the molecules with chemical bonding and so if the temperature increase, the rate of reaction will also be increased and so chemiosorption will also increase but Physiosorption is an exothermic process which releases energy during the adsorption , so when temperature increases it gets converted into chemiosorption and so the reaction changes.   For example, hydrogen gas is first adsorbed on nickel by van der Waals’ forces through phisiosorption at low temperature.BUt increasing the temperature the molecules of hydrogen then dissociate to form hydrogen atoms which are held on the surface by chemiosorption.