Question

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

• A. Adsorption is spontaneous.
• B. Adsorption increases with the increase in temperature.
• C. Both enthalpy and entropy of adsorption are negative.
• D. Adsorption on solid is reversible.

Answer 1

The correct option is B

Adsorption increases with the increase in temperature.

Explanation for correct option

(B) Adsorption increases with the increase in temperature

Physisorption

• Physical adsorption is also called physisorption.
• It occurs when physical factors such as Van der Waals forces hold the adsorbate gas molecules together.

Adsorption increases with the increase in temperature

• Physical adsorption reduces when the temperature rises because an increase in temperature causes molecules' kinetic energy to rise.
• Physical adsorption is an exothermic process.
• It happens more readily at lower temperatures and decreases as the temperature increases.

Explanation for incorrect options

(A) Adsorption is spontaneous

• Physical adsorption is a spontaneous process.
• The interaction between the adsorbent and adsorbate results in a decrease in randomness.

(C) Both enthalpy and entropy of adsorption are negative

• The bond enthalpy and entropy are negative in physical adsorption.
• Due to the interaction between the adsorbent and adsorbate results in a decrease in randomness.

(D) Adsorption on solid is reversible

• Adsorption occurs quickly and is reversible.
• It may readily be desorbed with heating or decompression.

Therefore the correct option is (B). Adsorption increases with the increase in temperature.