Adsorption of gases on solid surface is generally exothermic because

• A

  enthalpy is positive
• Correct answer
  B

  entropy decreases
• C

  entropy increases
• D

  free energy increases

Solution

Thermodynamics of adsorption:

i. $\mathrm{\Delta }\mathrm{S}<0$ because gaseous phase decrease
ii. $\mathrm{\Delta }\mathrm{G}<0$ because process is spontaneous
so $\mathrm{\Delta }\mathrm{G}=\mathrm{\Delta }\mathrm{H}-\mathrm{T}\mathrm{\Delta }\mathrm{S}$
$-\mathrm{v}\mathrm{e}=\mathrm{\Delta }\mathrm{H}-\left(+\mathrm{v}\mathrm{e}\right)\left(-\mathrm{v}\mathrm{e}\right)$
$\mathrm{\Delta }\mathrm{H}=-\mathrm{v}\mathrm{e}$
iii. $\mathrm{\Delta }\mathrm{H}<0$ so adsorption is an exothermic process.

Hence, the correct answer is option: 'B'.