Physical Chemistry – Chemical Equilibrium

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When does a system come to equilibrium?
answer

when it reaches a minimum total Gibbs energy G
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Equilibrium constant for partial pressures
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K_p = PI(partial pressure products) / PI(partial pressure reactants)
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Equilibrium constant for concentrations
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K_c = PI(concentration products) / PI(concentration reactants)
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Equilibrium constant scenario: K_p/c >>> 1
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equilibrium goes nearly to completion
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Equilibrium constant scenario: K_p/c > 1
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equilibrium favours the products
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Equilibrium constant scenario: K_p/c < 1
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equilibrium favours the reactants
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Equilibrium constant scenario: K_p/c = 1
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similar amounts of reactant and product at equilibrium
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Equation relating Kp and Kc?
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K_p = K_c*(R*T)^deltan
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Activity of Ideal Gas:
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a = p / 1bar
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Activity of Ideal Solution:
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a = concentration / 1M
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Activity of Pure liquid or Solid:
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a = 1
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Equilibrium constant for activities
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K = PI(activity products) / PI(activity reactants)
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Relationship between equilibrium constant of forward and reverse reactions:
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K_reverse = 1/K_forward
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Stoichiometry changes on equilibrium constants (change of stoich. by factor of n):
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K’ = K^n
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Equation for Solubility Product
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K_sp = [A]^a*[B]^b
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Direction of a Reaction: Q_c < K_c
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products tend to form
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Direction of a Reaction: Q_c = K_c
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equilibrium
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Direction of a Reaction: Q_c > K_c
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reactants tend to form
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Relationship between Gibbs energy and thermodynamic equilibrium constant, deltaG=
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deltaG = -R*T*ln(K)
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Relationship between thermodynamic equilibrium constant andGibbs energy, K=
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K = e^-(deltaG/R*T)
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The van’t Hoff equation
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ln(K) = deltaS/R – deltaH/(R*T)
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The van’t Hoff equation – at two temperatures
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ln(K_2/K_1) = – deltaH/R*(1/T_2 – 1/T_1)
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Equation: Molality
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m = moles of solute / kg of solvent

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