Equilibrium Systems and Stress Chemical Equilibrium Chemical

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Equilibrium Systems and Stress
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Chemical Equilibrium

• Chemical Equilibrium
• When the rates of the forward and reverse
  reactions are equal in a chemical reaction
• The concentration (amount) of reactants and
  products of the reaction remains the same
• Ex
• 2CO(g) O2(g) ? 2O2(g)

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Chemical Equilibrium
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Le Chatleliers Principle

• Stress something that causes a change in a
  system at equilibrium
• However, the system will adjust to this new
  stress and come back into equilibrium again
• This is LE CHATLELIERS PRINCIPLE

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Le Chateliers Principle

• This is LE CHATELIERS PRINCIPLE
• When a system at equilibrium is disturbed, the
  system adjusts in a way to reduce the change

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Le Chateliers Principle

• Chemical equilibria responds to three kinds of
  stress
• Changes in the concentration of reactants or
  products
• Changes in temperature
• Changes in pressure

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Le Chateliers Principle

• 1. Changes in concentration of reactants and
  products
• This is a model of the system at equilibrium.

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Changes in concentration of reactants and products

• If more reactants are added to the system, the
  equilibrium changes. The system will respond by
  making more product.

Stress is being added to the system here
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Changes in concentration of reactants and products

• 1 CO(g) 2H2(g) ?
  CH3OH(g)
• System at equilibrium
• System with added reactant CO
• To reach equilibrium again, the system will make
  more products
• The reaction will shift to the right (the
  forward reaction)

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Changes in concentration of reactants and products

• 1 CO(g) 2H2(g) ? CH3OH(g)
• System at equilibrium
• System with added product (CH3OH)
• To reach equilibrium, the system will make more
  reactants
• The reaction will shift to the left (reverse
  reaction)

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Effects of Temperature

• Temperature effects equilibrium the same way as
  concentration changes
• For exothermic forward reactions
• Increasing the temperature of an equilibrium
  system usually leads to a shift in favor of the
  reactants
• For endothermic forward reactions
• Increasing the temperature usually leads to a
  shift in favor of the products

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Effects of Temperature

• N2(g) O2(g) ? 2NO(g)
• System at Equilibrium
• System with added heat on the product side
• To reach equilibrium, the system will make more
  reactants
• The reaction favors the formation of reactants
  (reverse rxn)

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Effects of Pressure

• For solutions, pressure has almost no effect on
  the equilibrium
• Gases are greatly effected by changes in pressure
• An increase in pressure causes the system to
  shift its equilibrium position to REDUCE THE
  PRESSURE
• To reduce pressure, the system needs to reduce
  the number of gas particles

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Effect of Pressure

• Rule At constant temperature, increasing the
  pressure on a gas causes the system to shift in
  the direction that reduces the number of moles of
  gas

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Effects of Pressure

• Example
• N2O4(g) ? 2NO2(g)
• How many moles of gas are on the reactant
  side?_____
• How many moles of gas are on the product
  side?_____
• Which side has the greater amount of
  moles?________
• If adding pressure to this system causes the
  system to respond by reducing the number of moles
  of gas, which way will the reaction go?

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Real Life Applications

• The Bends
• Nitrogen and other gases are dissolved in our
  blood
• nitrogen(g) ? nitrogen(dissolved)
• As the diver comes up from the high pressures of
  the ocean, the equilibrium shifts to the left
• If they come up too fast, nitrogen bubbles form
  in the blood and other body fluids cause severe
  abdominal pain and maybe death