ENGR-1100 Introduction to Engineering Analysis

1
Lecture 24 Chemical equilibrium

• Equilibrium constant
• Dissociation of diatomic molecule
• Isotopic equilibrium
• Heterophase reactions

2
Gibbs free energy change
Chemical reaction
Gibbs free energy change
In equilibrium the Gibbs free energy change is
zero, therefore
3
Activity
Chemical potential
with
gives
4
Equilibrium constant
Defining standard free energy change for the
reaction
And equilibrium constant for the reaction
gives
5
Diatomic molecule
Equilibrium constant for the reaction
Chemical potential for monoatomic and diatomic gas
6
Diatomic molecule - equilibrium constant
7
Equilibrium pressure expression
Equilibrium constant for the reaction
Increasing temperature ? increasing
dissociation The major parameter controlling
dissociation is De/kT
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Isotopic equilibrium
Diatomic molecules isotopes A and B
Equilibrium constant
9
Isotopic equilibrium
Chemical potential
from
10
Heterophase reactions
Consider
aC 1 (activity of the pure solid phase)
Ka can be obtained from statistical mechanics
(e.q., Einstein model of C solid) or from
experiment via