The molar Gibbs free energy of a binary liquid mixture at atmospheric pressure and T ≥ 260K is given by the following:
G(x₁, T) = 2.75x₁⁴ – 6.6x₁3 + 0.025Tx₁" – 1.16641x₁" – 2x₁
(1) Sketch a qualitative phase diagram in the T-x₁ plane.
(2) If the mixture shows any two-phase behavior, give the equation for the spinodal curve and calculate the spinodal composition of component 1 in two phases at 260 K.
(3) Calculate any critical solution temperatures and critical composition of component 1.
(4) Explain why this equation is invalid for a binary liquid mixture and violates the classical thermodynamics. Please show step-by-step derivations. (Hint: Gibbs-Duhem equation)