Absorption of gases on solid surface generally exothermic .
According to this statement the ΔH − −ve
Condition for spontaneous process.
ΔG=−ve
During adsorption
ΔS=−ve
(ie) less than zero
ΔG=ΔH−TΔS
ΔS=−ve
the TΔS must be +ve
Now, reaction can only spontaneous or ΔG=−ve
If ΔH=−ve
Hence Absorption of gasses on solid surface generally exothermic because of decrease in entropy