BASIC THERMODYNAMIC PRINCIPLES

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BASIC THERMODYNAMIC PRINCIPLES
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CHEMICAL EQUILIBRIUM

• Consider the generalized chemical reaction
• aA bB ? cC dD
• When is this system at equilibrium?
• When none of its thermodynamic properties change
  with time.
• When the rate of the forward reaction exactly
  equals the rate of the reverse equilibrium.

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THERMODYNAMIC CRITERION OF EQUILIBRIUM

• ?rG c?fGC d?fGD - a ?fGA - b ?fGB - ...
• If ?rG 0, reaction is in chemical equilibrium.
• If ?rG lt 0, reaction will proceed in direction
  written.
• If ?rG gt 0, reaction will proceed in reverse
  direction.

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MOST GENERAL CASE
In the most general case a chemical reaction can
be written
In this case then
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SPECIFIC CASES

• For the reaction H2CO30 ? HCO3- H
• we obtain
• ?rG ?fGHCO3- ?fGH - ?fGH2CO30 0
• For the reaction Bi2S3(s) 6H ? 2Bi3 3H2S0
• we obtain
• ?rG 2?fGBi3 3?fGH2S0 - ?fGBi2S3(s) - 6?fGH
  0

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THE EQUILIBRIUM CONSTANT

• For the reaction
• aA bB ? cC dD
• we can define a constant called the equilibrium
  constant

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CHEMICAL ACTIVITY

• The chemical activity is related to the
  concentration
• ai ?ici
• where ai ? activity of species i ?i ? activity
  coefficient of species i ci concentration of
  species i. If the solution is dilute or ideal,
  then ?i 1 and ai ci.

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MOST GENERAL FORM OF EQUILIBRIUM CONSTANT
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SPECIFIC CASES

• For the reaction H2CO30 ? HCO3- H
• we obtain

For the reaction Bi2S3(s) 6H ? 2Bi3 3H2S0
we obtain
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RELATIONSHIP BETWEEN GIBBS FREE ENERGY OF
FORMATION AND ACTIVITY
RELATIONSHIP BETWEEN GIBBS FREE ENERGY OF
REACTION AND THE EQUILIBRIUM CONSTANT
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TEMPERATURE DEPENDENCE OF THE EQUILIBRIUM CONSTANT
Vant Hoff Equation
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EXAMPLE VANT HOFF PLOT