Chemical Equilibrium

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Chemical Equilibrium

• Lesson 4
• The Reaction Quotient More Equilibrium
  Calculations

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K vs. Q

• The reaction quotient, Q, is like K when the
  system is not at equilibrium.
• It is again the product of the concentration of
  the products divided by the concentration of the
  reactants, with molar coefficients as powers.
• Q Aa Bb
• Cc Dd
• for aA bB cC dD

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K vs. Q

• If the system is at equilibrium and you calculate
  Q, it will be the same value as K.
• If Q is less than K, that means that the system
  is not yet at equilibrium, so will need to shift
  to the right, towards the products.
• If Q is greater than K, that means the system is
  beyond the equilibrium, and so will need to shift
  to the left towards the reactants.

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Example 1

• For the synthesis of ammonia gas at 500C in a
  closed vessel from nitrogen and hydrogen gases,
  the equilibrium constant, K, is 6.01x10-2. For
  each of the following initial conditions,
  determine if the given concentrations represent
  an equilibrium. If not, predict the direction in
  which the reaction will proceed to reach
  equilibrium.
• NH3 1.00x10-3 mol/L
• N2 1.00x10-5 mol/L
• H2 2.00x10-3 mol/L
• NH3 2.00x10-4 mol/L
• N2 1.50x10-5 mol/L
• H2 3.54x10-1 mol/L
• c) NH3 1.00x10-4 mol/L
• N2 5.00 mol/L
• H2 1.00x10-2 mol/L

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Example 2

• Phosphorus pentachloride decomposes into
  phosphorus trichloride and chlorine. A 2.00 L
  sealed container at 30C initially contains 0.298
  mol of phosphorus trichloride gas, 8.70x10-3 mol
  of phosphorus pentachloride gas, and no chlorine
  gas. At equilibrium, the flask contains
  2.00x10-3 mol of chlorine gas. Calculate the
  equilibrium concentrations of all entities and
  the value of K.

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Example 3

• Carbon monoxide reacts with steam to produce
  carbon dioxide and hydrogen. At 700 K, the
  equilibrium constant is 5.10. Calculate all
  equilibrium concentrations if 1.250 mol of each
  entity in initially placed in a 500.0 mL sealed
  flask.

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Example 4

• Carbon dioxide decomposes into carbon monoxide
  and oxygen gas. At 2000C, K 6.40x10-7.
  Calculate the concentrations of all entities at
  equilibrium if 0.250 mol of CO2 is placed in a
  1.000 L closed container and heated.

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Example 5

• If 0.500 mol of dinitrogen tetroxide is placed in
  a 1.00 L closed container at 150C, what will be
  the concentrations of dinitrogen tetroxide gas
  and nitrogen gas at equilibrium?
• N2O4 (g) 2 NO2 (g). K 4.50 under these
  conditions.