In an irreversible process taking place at constant T and P and in which only PV work is being done, the change in free energy (dG) and change in entropy (dS) satisfy the criteria:
= -ve
ΔG=ΔH−TΔS
Since T is constant, DeltaH=0
Also, as the process is spontaneous, we can conclude from the above equation that:
△G = -ve
△S = +ve