Which one of the following chargcterisitic is associated with adsorption?

Options

A. `DeltaG` and `DeltaS` are negative but `DeltaH` is positive
B. `DeltaG` is negative but `DeltaH`and `DeltaS` are positive
C. `DeltaG` , `DeltaH` and `DeltaS` all are negative
D. `DeltaG` and `DeltaH` are negative but `DeltaS` is positive

Answer

C

Explanation

`Delta_(ads)H` (enthalpy of adsorption) is always negative because when adsorption takes place, the residual forces and/or unsatisfied valencies on the surface of the adsorbent decrease.`DeltaS` is also negative because as the molecules of the adsorbate are held on the surface of the adsorbent, entropy decreases `DeltaG` is negative because the process of adsorption is a spontaneous process (except at high temperature)