Which of the following is true with respect to adsorption ?

Options

A. `Delta lt 0, Delta gt 0, DeltaH lt 0`
B. `DeltaG lt 0, DeltaS lt 0, DeltaH lt 0`
C. `DeltaG gt 0, DeltaS gt 0, DeltaH lt 0`
D. `DeltaG lt 0, DeltaS lt 0, DeltaH gt 0`

Answer

B

Explanation

Adsorption is an exothermic process and hence, `DeltaH` is negative for adsorption. On the other hand the molecules of the adsorbate are held on the surface of the adsorbent and hence, they have lesser tendency to move about freely. In other words entropy decreases i.e., `DeltaS` is negative. According to Gibbs-Helmholtz equation, `DeltaG=DeltaH-T*DeltaS`
Thus for the process of adsorption to occur `DeltaG` must be negative. Hence, for adsorption
`" "DeltaG lt 0, DeltaS lt 0, DeltaH lt 0`