Calculate the change in entropy when a perfect gas is expanded to twice the volume and cooled to one half of the initial temperature. As the reaction advances and we move from left to right along the extent of reaction, the slope of the Gibbs energy changes.
Equilibrium corresponds to zero slope, or a change in free energy equal to zero.
When sum of the two contributions has a minimum. That minimum represents the equilibrium composition of the system. Vdp, and evaluate the integral for revesible adiabatic expansion.