Adsorption is spontaneous process $∆\mathrm{G}$ is -ve. During adsorption randomness of adsorbate molecules reduced and $∆{\mathrm{S}}_{\mathrm{total}}$ is +ve.

$∆\mathrm{G}=∆\mathrm{H}-\mathrm{T}∆\mathrm{S}$

$∆\mathrm{H}=∆\mathrm{G}+\mathrm{T}∆\mathrm{S}$

$∆\mathrm{H}$ is highly -ve and residual forces on surface are decreased.