Chem ch 14

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Chem ch 14
2010-05-01 22:36:13
Chemistry Chang

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  1. chemical equilibrium
    the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constant
  2. equilibrium constant
    • K = products over reactants raised to the power of their coefficients
    • it is a dimensionless quantity(unlike little k), don't worry about why
    • constant values unless temperature changes
    • If K<<1 - the denominator is much larger than the numerator, therefore the reactants are favored
    • If K >> 1 the equilibrium "lies to the right"
    • if you flip the reaction, invert K (4.0 --> 0.25)
  3. homogeneous equilibria
    • all reacting species are in the same phase
    • all are gasses
    • all are aqueous
  4. heterogeneous equilibria
    • reacting species exist in different phases
    • solids & gases
    • solids & liquids
    • don't include solids (s) and liquids (l) in the equilibrium constant only gases (g) or solutions (aq)
  5. relationship between Kc and Kp
    • PV =
    • Kp = Kc (RT)^ (to the power of the change in n)
  6. Dynamic Equilibrium
    in a reversable reaction reactants are always turning into products and products are always turning into reactants
  7. Le Chatelier's Principle
    • if an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset
    • *if adding a gas that doesn't appear in the balanced equation, it has no effect on equilibrium
  8. law of mass action
    for a reversible reaction at equilibrium and a constant temperature, a certain ratio of reactant and product concentrations has a constant value (K)
  9. multiple equilibria
    if a reaction can be expressed as the sum of 2 or more reactions, the equilibrium constant for the overall reaction is given by the product of the equilibrium constants of the individual reactions (Hess's law) Kc = Kc' x Kc"
  10. catalyst
    • lowers the activation energy for the forward and the reverse reaction to the same extent
    • doesn't alter the equilibrium constant, nor shifts the equilibrium
  11. How does temperature affect equilibrium?
    • temperature increase favors an endothermic reaction (+^H) - reactants + heat <=> products
    • temperature decrease favors an exothermic reaction (-^H) - reactants <=> products + heat
  12. reaction quotient Q
    • same form as K but is not at equilibrium
    • if Q < K the reaction must go forward (to the right) (form products) to reach equilibrium
    • if Q = K the reaction is at equilibrium
    • if Q > K the reaction must go backward (left, reactants) to reach equilibrium