16-3: Le Chatelier’s Principle

Le Chatelier’s Principle  If a change is made to a system at equilibrium, the rxn will shift in the direction that will allow it re-establish equilibrium

Concentration  Adding more of something increases the concentration and will cause the rxn to shift to the other side  Taking something out causes a decrease in conc. and the rxn will shift to that side

Why is it useful?  Le Chatelier’s Principle can be used to maximize the amount of product that a reaction produces.

How would you use a change in concentration to maximize the products?  2H 2 (g) + O 2 (g)  2H 2 O(g)  If, at equilibrium, there are more reactants than products, take away water as it is produced

Pressure  For gaseous equilibrium systems  If pressure is increased, the rxn will shift in the direction that produces fewer gaseous moles

2H 2 (g) + O 2 (g)  2H 2 O(g)  3 moles of gaseous reactants, 2 moles of gaseous products  Increase the pressure. This will push it to the side with fewer gaseous mols.

Temperature  Value of the equilibrium constant depends upon the temperature

Temperature  Is the rxn exothermic or endothermic? Exothermic – gives off heat. If given heat, absorbs it in the reverse rxn. Endothermic – requires heat. If heat is taken away, it gets more from the reverse reaction. Think of heat as a reactant or product.

Temperature  Exothermic: A + B  C + heat  To increase rate, cool it.  Endothermic: A + heat  B + C  To increase rate, heat it.

Temperature  Reaction rate is important, though.  If you cool a rxn too much, the particles do not collide and little to no reaction will occur.

Haber Process  Developed by German chemist, Fritz Haber, during WWI to help Germany produce ammonia for use in explosives

Haber and Einstein

Haber Process  N 2 (g) + 3H 2 (g)  2NH 3 (g) + heat  Removed ammonia as it was produced  Increased pressure  4 mols gaseous reactants, 2 moles gaseous products.

Haber Process  1914: Haber made head of chemical warfare service, works on gases for chemical warfare  1918: Haber wins the Nobel Prize in Chemistry  1933: Haber (who is Jewish) leaves Germany, as Hitler gains more power

Haber Process  Today, the Haber process is still used to make ammonia for fertilizers and cleaning products