# Physical Chemistry – Chemical Equilibrium Kelly Fisher
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When does a system come to equilibrium?

when it reaches a minimum total Gibbs energy G
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Equilibrium constant for partial pressures

K_p = PI(partial pressure products) / PI(partial pressure reactants)
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Equilibrium constant for concentrations

K_c = PI(concentration products) / PI(concentration reactants)
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Equilibrium constant scenario: K_p/c >>> 1

equilibrium goes nearly to completion
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Equilibrium constant scenario: K_p/c > 1

equilibrium favours the products
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Equilibrium constant scenario: K_p/c < 1

equilibrium favours the reactants
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Equilibrium constant scenario: K_p/c = 1

similar amounts of reactant and product at equilibrium
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Equation relating Kp and Kc?

K_p = K_c*(R*T)^deltan
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Activity of Ideal Gas:

a = p / 1bar
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Activity of Ideal Solution:

a = concentration / 1M
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Activity of Pure liquid or Solid:

a = 1
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Equilibrium constant for activities

K = PI(activity products) / PI(activity reactants)
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Relationship between equilibrium constant of forward and reverse reactions:

K_reverse = 1/K_forward
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Stoichiometry changes on equilibrium constants (change of stoich. by factor of n):

K’ = K^n
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Equation for Solubility Product

K_sp = [A]^a*[B]^b
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Direction of a Reaction: Q_c < K_c

products tend to form
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Direction of a Reaction: Q_c = K_c

equilibrium
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Direction of a Reaction: Q_c > K_c

reactants tend to form
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Relationship between Gibbs energy and thermodynamic equilibrium constant, deltaG=

deltaG = -R*T*ln(K)
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Relationship between thermodynamic equilibrium constant andGibbs energy, K=

K = e^-(deltaG/R*T)
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The van’t Hoff equation

ln(K) = deltaS/R – deltaH/(R*T)
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The van’t Hoff equation – at two temperatures