Equilibrium

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Equilibrium

• With your Chemistry 102 Host
• Dr. Mike Daniel

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Equilibrium

• aA bB ? cC dD
• _at_ Equilibrium Rate Forward Rate Backward
• H2O(L) ? H2O(G) Phase Equilibrium
• PH2O constant (Vapor Pressure)

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Equilibrium Simulation

• Simulated Equilibrium
• R Y ? B G
• Red Yellow ? Blue Green
• Simulation shows dynamic equilibrium, reaction
  going both directions
• After a period of time, concentrations constant

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Equilibrium

• aA bB ? cC dD
• Mass Action Expression for Homogeneous Rxn
• Q Cc Dd / AaBb
• Q Reaction Quotient

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Equilibrium

• aA bB ? cC dD
• Mass Action Expression
• Q Cc Dd / AaBb
• _at_ Equilibrium Qc Kc Equilibrium Constant

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Equilibrium

• aA bB ? cC dD
• Mass Action Expression for Partial Pressures
• Qp PDd PCc / PAa PBb
• _at_ Equilibrium Qp Kp Equilibrium Constant

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Kp and Kc Relationship

• Kp Kc (RT)?ng
• ?ng moles product gas - moles reactant
• Gas
• R.0821 L atm/K mol (assuming P in atm)

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Rxn Quotient and Equilibrium Constant

• H2I2 ? 2 HI Kc 49.5 _at_ 440.C
• If H2 I2 .05 M
• HI .2
• Q ?
• Reaction proceed to left or right?

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Compare Equilibrium Constants

• N2 O2 ? 2 NO
• Kc NO2 / N2 O2 4.8 X 10-31 (25 C)
• Equilibrium Mixture lies far to _________
• 2H2 O2 ? 2 H2O
• Kc 9.1 X 1080 (25 C)
• Equilibrium Mixture lies far to _________

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Thermodynamic Kp,c

• ?G ?Go RT LN (Q)
• ?G Gibbs Free Energy difference between
  equilibrium and Q concentrations
• ?Go ?Gfo(products) - ?Gfo(reactants)
• R 8.314 X 10-3 kJ /K mol
• ?G lt 0, Rxn proceeds toward Products
• (Similar to Q lt K)

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Thermodynamic Kp,c

• _at_ Equilibrium ?G 0 So
• ?Go - RT LN (K)
• K Kp Gas Phase Rxn (atm)
• K Kc Solution Phase (M)

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Thermodynamic Kp,c

• ?Go - RT LN (K)
• Measure K to calculate ?Go
• If ?Go known, calculate K
• Estimate ?GoT ? ?Ho25C - T ?So25C to estimate K
  _at_ T

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Thermodynamic Kp,c

• ?Go - RT LN (K)
• N2 O2 ? 2 NO
• Kc Kp 4.8 X 10-31 (25 C)
• ?Ho 180.8 kJ , ?So 24.7 J/K
• ?Go2400 K ? ?
• Kp ? ? (2400 K)

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Le Chateliers Principle

• If an outside influence upsets an ?, the system
  changes to counteract the disturbance , if
  possible, return the system to ?.
• Used to predict how ? shifts

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Le Chateliers Principle

• Look _at_
• A
• V
• T
• Catalysts
• Inert Gas

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Le Chateliers Principle A
_at_ Equilibrium After N2O4
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Le Chateliers Principle A

• Adding or removing Reactants or Products
• N2O4 ? 2 NO2
• _at_ ?
• Rate forward Rf kf N2O4 RbkbNO22
• Say increase PN2O4 to .500 atm
• How will rate forward/backward change?

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Le Chateliers Principle A

• Adding or removing Reactants or Products
• N2O4 ? 2 NO2
• Kp .140 (.212 atm)2 / .321
• Increase PN2O4 to .500 atm
• Q (.212 atm)2 / .5 0.090 lt Kp
• How does system respond?

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Le Chateliers Principle (Vg)

• Changing V (for gas phase only)
• Decrease V is equivalent to increasing P,
• P n RT
• V
• N2 3 H2 ? 2 NH3
• 4 mole reactant gas ? 2 moles product gas
• System reduces P by shifting ?

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Le Chateliers Principle (T)

• N2 3 H2 ? 2 NH3 ?Ho25C -92 kJ
• N2 3 H2 ? 2 NH3 92 kJ
• Increasing T makes more energy available
• System can reduce disturbance by consuming
  energy, by shifting in endothermic direction
• T only disturbance that changes K

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Le Chateliers Principle (T)

• N2 3 H2 ? 2 NH3 92 kJ
• Increasing T shifts rxn backwards
• ?Go25 C -33.4 kJ
• Kp 7.2 X 105
• ?Go500 C 61.3 kJ
• Kp 7.2 X 10-5

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Le Chateliers Principle (add catalysts)

• Catalysts lower Ea for forward and back rxn
• Speeds up forward and back equally
• Get to Equilibrium quicker,

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Le Chateliers Principle ( Inert Gas)

• Increases Ptotal, does not change Partial P
• PA nA RT
• V
• No change on Equilibrium

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Le Chateliers Principle

• N2O4 ? 2 NO2
• Endothermic or Exothermic?
• How will T increase shift ? ?
• How will P increase shift ? ?
• How will adding N2 ?

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Le Chateliers Principle
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Le Chateliers Principle
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Le Chateliers Principle NH3 Manufacturing
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H2(g) S(s) ? H2S(g) 20.6 kJ

• What is mass action expression?
• How will ______ shift reaction?
• Add hydrogen gas
• Add solid sulfur
• Remove hydrogen sulfide
• Decrease V
• T increase

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Calculate Final from K and Initial

• Start with H2 I2 2.00 M
• Kc 55.17 _at_ 699 K
• What are ? ?

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Concentration Table
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Concentration Table
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Concentration Table
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Mass Action Expression values from Final

• Kc HI2 / H2 I2 55.17
• 55.17 (2x)2 / (2.00 x) (2.00 x)
• Take Square Root of both sides
• Grind and solve for x
• Substitute x into Final Concentration table
  values
• X 1.58
• H2 I2 .42 M, HI 3.16