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Activity Coefficients

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). Activity Coefficients. Real solution: Deviation from ideality due. A (l) + B (l)  AB (l).

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Activity Coefficients

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  1. Activity Coefficients Ideal solution: xi , ci Raoult’s Law Chemical Potential Equilibrium constant N2(g) + 2 O2(g) 2 NO2(g)

  2. Activity Coefficients Real solution: Deviation from ideality due A(l) + B(l) AB(l) • Interaction (attraction) A-A ≠ attraction A-B • Interaction (attraction) B-B ≠attraction A-B • DHmix≠ 0: Ep(AB) ≠ Ep(A)+Ep(B) • VM(A) ≠ VM(B) : DVmix≠ 0 Ionic atmosphere: electrostatic interaction between the ions

  3. Activity Coefficients Raoult’s Law Chemical Potential Equilibrium constant N2(g) + 2 O2(g) 2 NO2(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 Na3PO4 aqueous solution at 25oC: Impossible to determine experimentally

  6. Impossible to determine experimentally Mean activity coefficient: g±

  7. Satisfactory only at low concentrations

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

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