Equilibrium Chemical reaction in which reactants are forming as fast as products yet the net concentrations of each remains constant A + B  C + D N 2 + 3H 2  2 NH 3

Equilibrium Constant K aA + bB  cC + dD K = [C]c [D]d [A]a [B]b Products over reactants

Equilibrium Constant K K > 1000 mostly products K <.001mostly reactants K =.001 to 1000 equilibrium condition

Lechatlier’s Principle If stress is applied to a system at equilibrium, the system will adjust to relive the stress

Lechatlier’s Principle Possible stresses occur with Concentration, Volume and Temperature

Change in concentration PCl 3 + Cl 2  PCl 5 At equilibrium, the molar concentrations are constant Add PCl 5 the reaction will shift to form more PCl 3 and Cl 2 remove PCl 5 the reaction will shift to form less PCl 3 and Cl 2 Add PCl 3 or Cl 2 more PCl 5 will form Remove PCl 3 and Cl 2 more will form

Change in volume Reducing the volume or increasing the pressure causes the equilibrium to shift to the side of the equation with the fewest moles N 2 g + 3H 2 g  2NH 3 g 4moles  2 moles H 2 g + Br 2 g  2HBr g 2moles  2moles

Temperature effects Exothermic Reactants  products + Heat H2 + O2  H2O Calories Endothermic Heat + Reactants  products CO2 + 2H Calories  CH 3 OH

Catalyst effect A catalyst speeds up the rate at which equilibrium is achieved but does not change anything else – this occurs due to lowering the activation energy