Question

The given graphs/data I, II, III and IV represent general trends for different physisorption and chemisorption processes under mild conditions of temperature and pressure. Which of the following choice(s) about I, II, III and IV is/are correct?

• A. I is physisorption and II is chemisorption
• B. I is physisorption and III is chemisorption
• C. II and IV both are chemisorption
• D. III and IV both are chemisorption

Answer 1

Answer: (A), (C)

II and IV both are chemisorption

In physisorption as temperature increases, the extent of adsorption decreases thus I and III are physisorptions.
Chemical adsorption first increases with increase in temperature upto a certain extent and then decreases regularly thus II is chemisorption.
In chemisorption, attractive forces between adsorbent and adsorbate molecules are strong chemical bond thus enthalpy of adsorption is high and of the order $80-240\text{kJ/mol}$. As in IV, $\Delta H_{\text{adsorption}}=150\text{kJ/mol}$, thus it also represents chemisorption.