Equilibrium Constants

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Equilibrium Constants
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• Recall At equilibrium, the rate of the forward
  and reverse reactions are equal

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The Equilibrium Constant, Keq

• For the reaction
• aA bB ? cC dD
• At equilibrium
• rfwd rrev
• kfwdAaBb krevCcDd
• kfwd CcDd
• krev AaBb
• Keq CcDd
• AaBb

Sub in rate law equation
Rearrange
Sub in Keq for kfwd/krev
Equilibrium constant
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Examples
Write the equilibrium constant expression for the
following two reactions
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Heterogeneous Equilibria

• Equilibrium systems can involve all states of
  matter
• However, the concentration of a pure solid or
  liquid cannot change
• Therefore, equilibrium constant expressions will
  not include solids and liquids

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Magnitude of Keq

• Keq gtgt 1 At equilibrium there is more products
  than reactants. The reaction is product
  favoured
• Keq 1 At equilibrium there is an equal
  amount of products and reactants
• Keq ltlt 1 At equilibrium there is more
  reactants than products. The reaction is
  reactant favoured

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Example

• Calculate the value of Keq for the following
  system

At Equilibrium CO2 0.0954 mol/L H2
0.0454 mol/L CO H2O 0.00460 mol/L
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Practice

• P. 442-445 1-6
• P. 448 1-9