[[Flash Separation - Mixture Properties]] The partial molar Gibbs free energy of a component in a mixture is known as the chemical potential, or $μ_i$. **Phases in equilibrium always have the same chemical potential**. For an ideal mixture, $ μ_i^{IGM} = G_i^{IG} + RTln(x_i)$$ For a real mixture, residuals are added: $μ_i = μ_i^{IGM} + G_i^{R} \qquad (G_i^R = RTln\phi_i)$ [[Fugacity of a component in a mixture]]