Question

The process of adsorption is always

• A. Exothermic
• B. Endothermic
• C. Isothermal only
• D. Non-spontaneous

Hint:

Remember that while adsorption can be endothermic or isothermal under specific conditions, it often releases heat (exothermic) due to the strong interaction between the adsorbent and adsorbate.

Answer 1

The Correct Option is A

Step 1: What is adsorption.
Adsorption is when gas or liquid particles stick onto the surface of a solid. We must decide if this process gives out heat or takes in heat.
Step 2: Think about the particles.
When particles stick to a surface, they slow down and lose freedom. Losing freedom means losing energy, and that lost energy comes out as heat.
Step 3: Use the free energy idea.
For adsorption to happen on its own, $\Delta G$ must be negative. Also the disorder falls, so $\Delta S$ is negative.
Step 4: Apply the formula.
From $\Delta G = \Delta H - T\Delta S$, with $\Delta G$ negative and $\Delta S$ negative, the term $-T\Delta S$ is positive. So $\Delta H$ must be even more negative to keep $\Delta G$ negative.
Step 5: Read the sign of heat.
A negative $\Delta H$ means heat is released. So adsorption gives out heat, which makes it exothermic.
Step 6: Final choice.
So adsorption is always an exothermic process.\[ \boxed{\text{Exothermic}} \]