Question

Which one of the following characteristics is associated with adsorption?

• A. $\Delta G$ and $\Delta H$ are negative but $\Delta S$ is positive.
• B. $\Delta G$ and $\Delta S$ are negative but $\Delta H$ is positive.
• C. $\Delta G$ is negative but $\Delta H$ and $\Delta S$ are positive.
• D. $\Delta G$, $\Delta H$ and $\Delta S$ all are negative.

Answer 1

The correct option is D

$\Delta G$, $\Delta H$ and $\Delta S$ all are negative.

As the adsorbate molecules are held on the surface of the solid adsorbent, entropy decreases i.e., $\Delta S=-ve,As\Delta G=\Delta H-T\Delta S$
For the adsorption to occur, $\Delta G=-ve$ and it is possible only if $\Delta H=-ve$.