Chemical Equilibrium A reversible reaction can go in either the forward or reverse directions A + B C D + Equilibrium is dynamic as both the forward and reverse reactions continue At equilibrium the forward and reverse rates are equal

Le Chateliers Principle If a stress is applied to a system at equilibrium, the system adjusts to relieve the stress CoCl42- H2O Co(H2O)62+ + 4Cl- + H= - H= + Exothermic (Heating) Endothermic ( Cooling)

CrO42- Cr2O72- Le Chatelier’s Principle If a stress is applied to a system at equilibrium, the system adjusts to relieve the stress CrO42- Cr2O72- + H2O 2H+ +

Fe(CNS)2- FeCl3 Le Chateliers Principle If a stress is applied to a system at equilibrium, the system adjusts to relieve the stress Fe(CNS)2- FeCl3 + CNS- + 3Cl-

Le Chatelier’s Principle CoCl42- H2O Co(H2O)62+ + 4Cl- + H= + H= - Exothermic (Heating) Endothermic ( Cooling) What happens if the red solution is heated ? Heating is a stress Le Chatelier states the opposing reaction occurs The cooling reaction occurs ie the reverse reaction Turning red into blue

Haber process 2 NH3 N2 3 H2 NH3 N2 H2 Manufacture of ammonia NH3 for the fertilizer industry 2 NH3 N2 3 H2 H= - 92.4 + 2 NH3 Kc = 3 N2 H2 x

Haber process Manufacture of ammonia NH3 for the fertilizer industry 2 NH3 N2 3 H2 H= - 92.4 + Le Chatelier’s principle predicts the yield of NH3 is maximised by Low temperature High pressure Actual temp used is 500oC (as lower temp reduces the rate ) Pressure used is 200 ATM

Contact process Manufacture of Sulfuric acid H2SO4 2 SO3 2SO2 O2 + Le Chatelier’s principle predicts the yield of SO3 is maximised by Low temperature High pressure Actual temp used is 450 oC (as low temp reduces the rate ) Pressure used is 1 ATM