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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 .
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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? • 2H2(g) + O2(g) 2H2O(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
2H2(g) + O2(g) 2H2O(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 Process • N2 (g) + 3H2(g) 2NH3 (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