This is a conceptual question. Many times we work with the gibbs energy of mixing under conditions of constant temperature but not pressure. In a problem like this:
Suppose that 2.0 mol H2 at 2.0 atm and 25 ∘C and 4.0 mol N2 at 3.0 atm and 25 ∘C are mixed at constant volume. Calculate ΔmixG.
Is easy to calculate that the Gibbs mixing energy is -9,7 kJ. But we also know that we cannot use gibbs' spontaneity criterion because it only works on constant pressure and temperature.
Is there any way to determine the entropy of the universe in this case to establish a criterion of spontaneity? *For example if we know that the total volume is 10L and the division is even.