Which of the following statement is correct for the spontaneous adsorption of a gas?

Options

A. `DeltaS` is negative and therefore, `DeltaH` should be highly positive
B. `DeltaS` is negative and therefore, `DeltaH` should be highly negative
C. `DeltaS` is positive and therefore, `DeltaH` should be negative
D. `DeltaS` is positive and therefore, `DeltaH` should also be highly positive

Answer

B

Explanation

`DeltaS` (change in entropy) and `DeltaH` (change in enthalpy) are related by the equation
`DeltaG=DeltaH-TDeltaS` (here, `DeltaG`=change in Gibbs free energy)
for adsorption of a gas, `DeltaS` is negative because randomness decreases.
Thus, in order to make `DeltaG` negative (for spontaneous reaction), `DeltaH` must be highly negative.