Applied Geochemistry & Lab Ch.2 Thermodynamics of Solutions JYU

1. DEFINITIONS Solution: A single homogeneous phase resulted from the dissolution of two or more compositionally different phases (end members) . End members: The (real or imaginary) component phases to form a solution Exsolution: Separation (phenomenon) into two or more different phases from a solution

2. Generals Composition of a solution phase 𝑆= 𝑋 𝐴 𝐶 𝐴 + 𝑋 𝐵 𝐶 𝐵 + 𝑋 𝐶 𝐶 𝐶 +… = 𝑖 𝑋 𝑖 𝐶 𝑖 where X =mole fractions C=chemical compositions of the end members 𝑖 𝑋 𝑖 =1 𝑋 𝑖 = 𝑛 𝑖 𝑗 𝑛 𝑗

Gibbs free energy of a solution Gibbs free energy of mechanically mixed phases Gibbs free energy of mixing (solution forming) 𝐺 𝑠𝑜𝑙 = 𝐺 𝑚𝑒𝑐ℎ + 𝐺 𝑚𝑖𝑥 (Will be duscussed this in much more detail later)

3. Preliminary Knowledge Do you know Roult’s law, Henry’s law, Partial molal properties, Fugacity, Activity, Gibbs-Duhem equation, and Standard state (in thermodynamics)?

5. Chemical Potential Definition: 𝜇 𝑖 = 𝜕𝐺 𝜕 𝑛 𝑖 𝑇, 𝑃, 𝑛 𝑗 Example: For a system having two phses A & B, The Gibbs free energy of the system 𝐺 𝑠𝑦𝑠 = 𝑛 𝐴 𝜇 𝐴 + 𝑛 𝐵 𝜇 𝐵 𝑑𝐺 𝑠𝑦𝑠 = 𝜇 𝐴 𝑑 𝑛 𝐴 + 𝜇 𝐵 𝑑 𝑛 𝐵 For a closed system, 𝑑 𝑛 𝐴 =−𝑑 𝑛 𝐵 At an equilibrium state, 𝑑𝐺 𝑠𝑦𝑠 =0 Thus, 𝜇 𝐴 = 𝜇 𝐵