I have learnt that ΔG is the amount of available energy. So to understand it i used a simmple body system rather than chemical reaction,which is the sliding of a block on a fixed wedge(height h and inclination angleθ). 1)my system is ball -earth and rest surrounding both in thermal eqilibrium at temprature T 2)Now as per the definition H=U+PV, ΔH in this case would be -mgh. 3)If we consider that the wedge is frictionless the amount of energy that we could obtain when the ball reaches floor =mgh,hence the term TΔS=0.Hence the ΔS of both system and surroundings =0(because there is no transfer of heat even if we carry out this process reversibly) therfore ΔS of universe is 0. which contradicts the fact that this process was irreversible which must accompany increase in entropy of universe. Can anyone please point out the mistake in this.I also had a contradictory situation when i assumed the wedge to have a friction coefficient.