For the adsorption of a gas on a solid surface, the signs of Delta H and Delta S of the process are, respectively:

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For the adsorption of a gas on a solid surface, the signs of $Δ H$ and $Δ S$ of the process are, respectively:

Adsorption releases energy, so

Δ H < 0

. Gas molecules lose freedom of motion when held on the surface, so

Δ S < 0

. Spontaneity (

Δ G < 0

) therefore requires

∣Δ H ∣ > ∣ T Δ S ∣