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Le Châtelier’s Principle: Effect of Common Ions

Explore how stress impacts equilibrium states as per Le Châtelier's Principle, including changes in concentration, temperature, and pressure, and the Common Ion Effect in reactions. Learn through demos and homework tasks for enhanced understanding.

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Le Châtelier’s Principle: Effect of Common Ions

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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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