11.2 - Equilibrium Law

• homogenous equilibrium

  everything is in the same phase
• equilibrium law

  a quantitative law for predicting the amounts of reactants and products when a reversible reaction reaches dynamic equilibrium

  only constant for a particular temperature
• Kc for homogenous equilibrium

  include all substances in equilibrium constant because they are all in the same phase
• equilibrium constant equation

  for aA + bB <=> cC + dD

  Kc = ([C]^c[D]^d) / ([A]^a[B]^b)

  [...] = concentrations in mol dm^-3
• general method to find Kc by experiment

  mix measured quantities of reactants and/or products and allow for mixture to reach equilibrium

  analayse mixture to find equilibrium concentration of one of the chemicals

  use balanced equation and inital amounts to find equilibrium concentrations of reactants and products
• methods for measuring concentration at equilibrium without shifting equilibrium

  dilute equilibrium mixture

  remove catalyst

  reduce rate by cooling

  titrate against an alkali to find concentration of an acid
• heterogenous equilibria

  equilibrium system where reactants and products are in different phases
• Kc for heterogenous equilibrium

  doesn't include solids, pure liquids and water in dilute substances
• Kc < 1 x 10^-10


  reaction doesn't go
• Kc ~ 0.01

  equilibrium where reactants predominate
• Kc = 1

  equilibrium with roughly the same amounts of reactants and products
• Kc ~ 100

  equilibrium where products predominate
• Kc > 1 x 10^10

  reaction goes to completion