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