Chemical Equilibrium chapter 13

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Chemical Equilibriumchapter 13

• Sune Nørhøj Jespersen

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Goals

• After this lecture you should be able to
• describe conditions for chemical equilibrium
• define equilibrium constant K
• explain how to calculate K

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Two state chemical reactions

• Examples
• folding of proteines A open state, B compact
  state
• phase transition Aphase I, Bphase II
• binding of ligands to substrates A free state,
  B bound state

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Two state chemical reactions
K
A
B
Number of A state etc.
Fixed temperature and pressure
Gibbs free energy
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Two state chemical reactions
Constraint
At chemical equilibrium, the chemical potentials
are equal.
The chemical potential can be calculated from the
partition function.
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Reaction coordinates
Toward equilibrium,
have opposite sign. System tends to escape phase
with higher ( is escaping tendency)
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Equilibrium constant
Ideal gas only
For the equilibrium constant
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More complex reactions
Constraint
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More complex reactions
For ideal gases
so
and
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Ground state energy
Vibrations can dissociate diatomic molecules
E
D dissociation energy
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Example
So mainly driven by rotational entropy
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Pressure based equilibrium
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Vant Hoff
depends not on pressure, only temperature
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Vant Hoff
Generally
Equivalently
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Vant Hoff
If and temperature independent
Vant Hoff
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Vant Hoff
Likewise we find
with
and