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Le Ch â telier’s Principle and the Common Ion Effect

Le Ch â telier’s Principle and the Common Ion Effect. Stress. Something that causes a change in a system at equilibrium . Stress disrupt equilibriums. After the stress is applied, the equilibrium has to readjust . This phenomenon was studied by the chemist Henri Le Ch â telier.

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Le Ch â telier’s Principle and the Common Ion Effect

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  1. Le Châtelier’s Principle and the Common Ion Effect

  2. Stress • Something that causes a change in a system at equilibrium. • Stress disrupt equilibriums. After the stress is applied, the equilibrium has to readjust. • This phenomenon was studied by the chemist Henri Le Châtelier.

  3. Le Châtelier’s Principle • The principle that states that a system in equilibrium will oppose a change in a way that helps eliminate the change. • In other words, either products or reactants will form to reach a new equilibrium.

  4. Types of Stress • Changes in the concentration of reactants or products • Changes in temperature • Changes in pressure

  5. Changes in the concentration of reactants or products • The addition of more reactants will shift the equilibrium to make more products. • The addition of more products will shift the equilibrium to make more reactants.

  6. Changes in temperature • For exothermic reactions, increasing the temperature of an equilibrium mixture usually leads to a shift to form more reactants. • For endothermic reactions, increasing the temperature of an equilibrium mixture usually leads to a shift to form more products.

  7. Why? • Energy can either be a product or reactant • In exothermic reactions A + B C + D + energy • In endothermic reactions A + B + energy C + D

  8. Change in Pressure • Mainly have an effect if there are gases present in the reaction. • Increase in pressure will favor side of equation that has the smaller volume (or fewer gas particles). • Which side would be favored: • 2NOCl (g) 2NO(g) + Cl2(g) • H2O (g) + CO(g) H2(g) + CO2(g)

  9. The Common Ion Effect • The phenomenon in which the addition of an ion common to two solutes brings about precipitation or reduces ionization. • Why? • The common ions act as more product in these cases. • CuCl (s) Cu+1(aq) + Cl-1(aq) • What happens if we add NaCl?

  10. Demos [Cu(H2O)4]+2 + 4Cl-1 [CuCl4]-2 + 4 H2O blue green NH3 + H2O  NH4+1 + OH-1 Add some phenolphthalein (Indicator), which turns pink when OH-1 is present

  11. Homework • Page 522: 18-20 • Le Châtelier's Principle Worksheet

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