Give an example where physisorption changes to chemisorption with rise in temperature. Explain the reason for change.

(N/A) The adsorption of hydrogen on finely divided nickel at low temperatures is due to weak van der Waals' forces,which is an example of physisorption.
When the temperature is raised,the $H_2$ molecules gain enough energy to dissociate into $H$ atoms.
These $H$ atoms then form strong chemical bonds with the nickel surface,resulting in chemisorption.