# Physical Chemistry – Chemical Equilibrium

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