How adsorption is an exothermic reaction..???

During adsorption there is a decrease in the residual attractive forces present on the surface of the adsorbent, leading to decrease in the surface energy of the adsorbent, which is evolved as heat. Thus, the enthalpy of adsorption is negative and thereby, adsorption is essentially an exothermic process.

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since, ΔH of adsorption is always negative. When a gas is adsorbed on a solid surface, its movement is restricted leading to a decrease in the entropy of the gas i.e., ΔS is negative. Now for a process to be spontaneous, ΔG should be negative.


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Since ΔS is negative, ΔH has to be negative to make ΔG negative. Hence, adsorption is always exothermic.

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