1. Activity Coefficients Ideal solution: x i, c i Raoult’s Law Chemical Potential Equilibrium constant N 2(g) + 2 O 2(g)  2 NO 2(g)

2. Activity Coefficients Real solution: Deviation from ideality due - Interaction (attraction) A-A ≠ attraction A-B - Interaction (attraction) B-B ≠ attraction A-B -  H mix ≠ 0: E p (AB) ≠ E p (A)+E p (B) - V M (A) ≠ V M (B) :  V mix ≠ 0 A (l) + B (l)  AB (l) Ionic atmosphere: electrostatic interaction between the ions

3. Activity Coefficients Raoult’s Law Chemical Potential Equilibrium constant N 2(g) + 2 O 2(g)  2 NO 2(g) Ideal if

4. Activity Coefficients -Very difficult to calculate - composition/concentration dependent -Debye and Hückel: activity coefficient of ions in solution -Only electrostatic effects were considered -Point charges (zero volume) -The deviation from ideality that ionic atmosphere formation causes was attempted to calculate Debye-Hückel Limiting Law: DHLL

5. Debye-Hückel Limiting Law Given: 0.10 M Na 3 PO 4 aqueous solution at 25 o C: Impossible to determine experimentally

6. Mean activity coefficient:  ±

8. Satisfactory only at low concentrations

9. One Modification: Ions are not point charges Limited application