Question

Which one of the following characteristics is associated with adsorption?

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

Answer 1

The correct option is A $\Delta G,\Delta H\text{and}\Delta S$ all are negative.

As the molecules of the adsorbate 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 $\Delta H=-ve$.