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Question

# Why is the enthalpy of adsorption negative?

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Solution

## Adsorption Enthalpy: Adsorption enthalpy is the heat released or absorbed during the adsorption process as defined by thermodynamics.Explanation:Adsorption is the process of attracting molecules of adsorbate to the adsorbent's surface. As a result, energy is released, and the heat of adsorption is negative, implying that adsorption is always exothermic.As per Gibb's energy equation: $\mathrm{\Delta G}=\mathrm{\Delta H}-\mathrm{T\Delta S}$For a process to be spontaneous $\mathrm{\Delta G}<0$.As it is an exothermic reaction, so the entropy of the system decreases because the atoms are more ordered at lower temperatures. so $\mathrm{\Delta S}<0$.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.

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