EquilibriumChemical reaction in which reactants are forming as fast as products yet the net
concentrations of each remains constant
A + B C + D
N2 + 3H2 2 NH3
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 < .001 mostly 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
PCl3 + Cl2 PCl5
At equilibrium, the molar concentrations are constant
Add PCl5 the reaction will shift to form more PCl3 and Cl2
remove PCl5 the reaction will shift to form less PCl3 and Cl2Add PCl3 or Cl2 more PCl5 will form
Remove PCl3 and Cl2 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
N2 g + 3H2 g 2NH3 g
4moles 2 moles
H2 g + Br2 g 2HBr g
2moles 2moles
Temperature effects
Exothermic
Reactants products + Heat
H2 + O2 H2O + 700 Calories
Endothermic
Heat + Reactants products
CO2 + 2H2 + 90.7 Calories CH3OH
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
E
AB
EaEa