Surface Chemistry

Which one of the following characteristics is not correct for physical adsorption?

  1. Both enthalpy and entropy of adsorption are negative.
  2. Adsorption is spontaneous.
  3. Adsorption increases with increase in temperature.
  4. Adsorption on solids is reversible.

Answer

During adsorption, there is always decrease in surface energy which appears as heat. Therefore adsorption always takes place with evolution of heat, i.e. it is an exothermic process and since the adsorption process is exothermic, the physical adsorption occurs readily at low temperature and decreases with increasing temperature. (Le Chatelier's principle).

The correct option is C.