Question

Why is the enthalpy of adsorption negative?

Answer 1

Adsorption Enthalpy:

Adsorption enthalpy is the heat released or absorbed during the adsorption process as defined by thermodynamics.

Explanation:

1. Adsorption is the process of attracting molecules of adsorbate to the adsorbent's surface.
2. As a result, energy is released, and the heat of adsorption is negative, implying that adsorption is always exothermic.
3. As per Gibb's energy equation: $\mathrm{\Delta G}=\mathrm{\Delta H}-\mathrm{T\Delta S}$
4. For a process to be spontaneous $\mathrm{\Delta G}<0$.
5. As it is an exothermic reaction, so the entropy of the system decreases because the atoms are more ordered at lower temperatures. so $\mathrm{\Delta S}<0$.
6. From the above equation, we can say that if $\mathrm{\Delta G}<0\mathrm{and}\mathrm{\Delta S}<0$ then $\mathrm{\Delta H}<0$.

Thus, the enthalpy of adsorption is negative.