According to the assumptions of Constant P and T and no non mechanical work, we get
But there is another form of the Gibbs free energy equation which takes Reversible process and no non mechanical work as assumption
If I Use the assumptions constant Pressure and Temperature, according to the above equation we get dG=0,which contradicts the first equation.
What is the mistake I am making? Also, when ΔGsystem=-TΔStotal