-Chemical Equilibrium -Equilibrium Constant

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-Chemical Equilibrium -Equilibrium Constant

• Honors Chemistry
• Mrs. Coyle

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Equilibrium Position
http//www.chm.davidson.edu/ronutt/che115/K/Sol_1.
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Equilibrium Expression (Mass Action
Expression)Equilibrium Constant, Keq

• The concentrations are at the equilibrium
  position.
• The Keq is constant for a given temperature
  regardless of the initial concentrations.

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• Keq gt 1, products favored in equilibrium
• Keq lt 1, reactants favored in equilibrium
• Keq is not expressed with units.

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Rules for Keq of Heterogeneous Equilibrium
(more than one phase)

• Only gases and solutes concentrations appear in
  the equilibrium expressions.
• Pure liquids and solids do not affect the Keq,
  because they do not change.

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Practice

• 2 SO2(g) O2(g) ? 2 SO3(g) Keq
• AgCl(s) ? Ag (aq) Cl-(aq) Keq

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Ex. 1 Calculate the Keq , given equilibrium
concentrations

• N2O4 (g) ? 2 NO2(g)
• At equilibrium at 10C, N2O4 0.0045 M and
  NO2 0.030M.Calculate the Keq.
• Answer
• Keq 0.20

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Ex. 2 Calculate the Equilibrium Concentrations
from Keq and Initial Concentrations

• For the reaction A ? B the initial
  concentration of
• A 0.850 M , B0 and Keq 24. Find the A and
  B
• when equilibrium is reached.
• ICE Chart A B
• Initial 0.850 0
  
• Change -x x
• Equilibrium 0.850-x 0 x

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Ex.2 Contd

• Keq B
• A
• Answer
• X0.816 M,
• Equilibrium concentrations
• A 0.034M, B0.816M

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Reaction Quotient, Q

• A mass action expression at a position away from
  equilibrium.
• Q Cc Dd / Aa Bb
• If Q Keq , the position is at equilibrium
• If Q lt Keq , the reaction proceeds to the right
  to equilibrium.
• If Q gt Keq , the reaction proceeds to the left
  to equilibrium.

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Ex. 3 The Haber Process of Ammonia Production

• At 500oC, Keq 0.080, for the production of
  ammonia gas from nitrogen gas and hydrogen gas.
  Given that NH30.0596M, N20.600M, and
  H20.430M, find Q and predict how the reaction
  will proceed.
• Answer Q0.0745,reaction proceeds to the right