ACTIVITY:

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ACTIVITY

• EQUILIBRIUM CONSTANTS ARE A LIE!
• KS ARE NOT CONSTANT!
• Molar Actual
• Solubility Predicted
• KNO3
• Equilibrium is dependent ACTIVITY
• not concentration.

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AN EXAMPLE

• THE BIG PICTURE Hg2(IO3)2
• 
  Hg KNO3
• 6.9 x 10-7
  M 0
• 1.0 x 10-6
  M 0.050 M

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THE SMALL PICTURE

• PURE
  SOLVENT
• ANIONS
• CATION
• 
  IONIC ATMOSPHERE
• HIGH TOTAL
• 
  ION CONCENTRATION
• SMALLER IONIC RADIUS

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ACTIVITIES

• Account for total ion concentration
• aA bB ?? cC dD
• REAL K
• EQUILIBRIUM
• CONSTANT
• Activities
  Activity
• 
  Coefficient

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ACTIVITY COEFFICIENTS FOR CHARGED IONS
Extended Debye Huckel Equation

• Z Charge
• ? Ionic Strength
• ? - Effective size of hydrated ion (pm)
• See Table 6-1 page 91

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Calculations

• Calculate the ionic strength of a 0.023 M
  solution of Mg(NO3)2.

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• Use activities to calculate the molar solubility
  of lead iodide, PbI2, in a solution with an ionic
  strength of 0.050 M.
• Ksp PbI2 7.9 X 10-9

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ACTIVITY COEFFICIENTS OF NONIONIC COMPOUNDS

• Neutral species have no ionic atmosphere
• Activity Coefficient 1 for dilute solutions.
• lt 1M

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GASES

• Activity coefficient for a gas is FUGACITY
  COEFFICIENT
• Below P 1atm, 1
• Deviation from ideal gas behavior ?
• deviations from unity for fugacity