1. Applied Geochemistry & Lab Ch.2 Thermodynamics of Solutions
JYU

2. 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

3. 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

4. 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)

5. 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)?

6. 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