Chemical Equilibrium

• le chatelier's principle

  • if a reaction under dynamic equilibrium is subject to change, then the position of the equilibrium will shift to minimise the change
• effect of changing concentration on the equilibrium position

  • a chaange in concentration of reactants or prodicts will result in a shift in position of equilibrium
  • increased OH- eqm shifts to the right (forwards rxn rate increases) colourless
  • decreased OH- eqm shifts to the left, increases I2, brown
• effect of pressure on equilibrium

  • In gaseous reaction, increased pressure, eqm shifts to side with fewer gas moles
  • In gaseous reaction, decreased pressure, eqm shifts to side with more gas moles
• Dynamic Equilibrium

  no observational change - nothing appears to be happening

  -> however system is dynamic (in constant motion)

  a chemical system is in dynamic equilibrium when :

  • the concentrations of the reactants + products remain constant
  • the rate of the forward reaction is the same as the reverse reaction
• An equilibrium only happens as long as the system remains isolated

  • In an isolated system, no materials are added or taken away + no external conditions, such as temperature or pressure,are being altered
• Position of equilibrium

  not established until the reaction has been occurring for a period of time, immediate to days

  • once concentrations of reactants + products have become stable + forward and reverse rates are the same, equilibrium is said to have been established
• Factors affecting position of equilibrium

  A reversible reaction only remains in dynamic equilibrium when it is isolated in a closed system

  It can be altered :

  • concentration of reactants + products
  • pressure in reactants involving gases
  • temperature