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Le Chatelier’s Principle

Le Chatelier’s Principle. If an equilibrium is disturbed by:- 1) Adding or removing reactants or products; 2) Changing the pressure; 3) Changing the temperature; the equilibrium will shift to oppose the change. 1) Adding or Removing Reactants or Products.

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Le Chatelier’s Principle

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  1. Le Chatelier’s Principle • If an equilibrium is disturbed by:- 1) Adding or removing reactants or products; 2) Changing the pressure; 3) Changing the temperature; the equilibrium will shift to oppose the change.

  2. 1)Adding or Removing Reactants or Products chromate / dichromate equilibrium CrO42_(aq) + 2H+(aq) Cr2O72_(aq) + H2O(l) Yelloworange • Adding Acid disturbs the equilibrium, adding a reactant (H+ ions). • The equilibrium position will shift to the right to oppose the change. • This shift removes the excess H+ ions and converts chromate ions to dichromate ions (the solution changes from yellow to orange) • Adding Alkali disturbs the equilibrium, removing a reactant ( H+ ions) • The equilibrium position will shift to the left to oppose the change. • This shift produces more H+ ions and converts dichromate ions to chromate ions (the solution changes from orange to yellow).

  3. 2) Changing the Pressure • An increase in pressure will shift the equilibrium in the direction that produces the least moles of gas. • e.g. 2NO2 (g) N2O4 (g) Brown Colourless 2 moles 1 mole This equilibrium would shift to the right if the pressure was increased (turning colourless). This would oppose the increase in pressure, because there are less moles of gas on the right hand side of the equation.

  4. 3) Changing the Temperature • Increasing the temperature will shift the equilibrium in the direction that absorbs energy (endothermic). exothermic • e.g. 2NO2 (g) N2O4 (g) Brown Colourless endothermic This equilibrium would shift to the left if the temperature was increased (turning brown). This would oppose the increase in temperature, because the reverse reaction absorbs energy (endothermic).

  5. Catalysts • Catalysts don’t shift an equilibrium one way or the other. • They just increase the rate of attainment of equilibrium (they speed up the forward and reverse reactions).

  6. CO2 and the Oceans • CO2(g) + aq CO2(aq) • CO2(aq) + H2O(l) HCO3_(aq)+ H+(aq)

  7. Le Chatelier’s Principle • If an equilibrium is disturbed by:- 1) Adding or removing reactants or products; 2) Changing the pressure; 3) Changing the temperature; the equilibrium will shift to oppose the change.

  8. Br2 The Oscillating Reaction 3CH2(CO2H)2(aq) + 4BrO3-(aq) 4Br-(aq) + 9CO2(g) + 6H20(l) Mn2+ catalyst

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