N2O4(g) energy ? 2 NO2(g) (colourless) (reddish-brown)

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N2O4(g) energy ? 2 NO2(g)(colourless)
(reddish-brown)
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Le Chateliers Principle

• When a chemical system at equilibrium is
  disturbed by a stress, the system adjusts
  (shifts) to oppose the change
• Stresses include
• Change in concentration
• Change in pressure (or volume)
• Change in temperature

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Change in Concentration
A(g) 3B(g) ? 2C(g) heat

• Increasing the concentration of the reactants OR
• Decreasing the concentration of the products
• Will favour the forward reaction, causing the
  equilibrium to shift to the RIGHT
• Decreasing the concentration of the reactants OR
• Increasing the concentration of the products
• Will favour the reverse reaction, causing the
  equilibrium to shift to the LEFT
• RECALL Addition or removal of solid or liquids
  does not change the concentration. Therefore does
  not cause a shift. I.e. only applies to gases and
  aqueous solutions.

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Change in Concentration
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N2(g) 3H2(g) ? 2NH3
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Change in Pressure
? volume ? pressure ? volume ? pressure
A(g) 3B(g) ? 2C(g) heat

• Increasing the volume of the container OR
• Decreasing the pressure
• Will cause a shift to the side with MORE gas
  molecules
• In our example, it will shift left (4
  molreactants gt 2 molproducts)
• Decreasing the volume of the container OR
• Increasing the pressure
• Will cause a shift to the side with LESS gas
  molecules
• In our example, it will shift right (4
  molreactants gt 2 molproducts)

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Change in Temperature

• In an exothermic reaction
• Increasing the temperature will cause a shift to
  the LEFT
• Decreasing the temperature will cause a shift to
  the RIGHT

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Change in Temperature

• In an endothermic reaction
• Increasing the temperature will cause a shift to
  the RIGHT
• Decreasing the temperature will cause a shift to
  the LEFT

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Change in Temperature
Recall Keq is temperature dependent. Therefore,
changes in temperature will also affect Keq Shift
right ? products, ? Keq Shift left ?
reactants, ?Keq
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Variables that do NOT Affect Equilibrium

• Catalysts
• Increases reaction rate by lowering activation
  energy (of BOTH the forward and the reverse
  reactions equally)
• Decreases the time required to reach equilibrium
  but does not affect the final position of
  equilibrium
• Inert Gases
• Increases the pressure, which will increase
  reaction rate
• Increases the probability of successful
  collisions for BOTH products and reactants
  equally
• Decreases the time required to reach equilibrium
  but does not affect the final position of
  equilibrium

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Practice!

• Read p. 450-456
• P. 457 1-6
• P. 459 1-6