Why Adsorption is an exothermic process?

Adsorption is a exothermic reaction:

                             As we know adsorption is the interaction of adsorbate to adsorbent ,so there established a force of attraction between them ,which results in loss of heat .Hence it is exothermic process.Also decrease in residual forces causes decrease in surface energy of surface of adsorbent.

                                         G=H-TS

 According to above equation if the system is exothermic the value of G should be negative .As there is a gas adsorbed on the solid surface ,gas movement is constraint and hence decreasing its entropy i.e lacking of orderness.And for adsorption H is always negative so the process is exothermic.