Outline of Lecture 17: Chemical Equilibria
Text: Atkins Chapter 9 (all)
The general form of an equilibrium constant for the reaction:
aA
+
bB
=
cC
+
dD
is the following expression:
K
=
(activity of C)
c
(activity of D)
d
/(activity of A)
a
(activity of B)
b
where the activities are determined at equilibrium.
If not at equilibrium, then the ratio equals Q.
The activity of an ideal gas is its partial pressure.
The activity of a compound in a liquid or solution phase is essentially the same as its
concentration.
The activity of a solid is unity (the number 1).
The activity of a nearly pure liquid is also 1.
A high activity of a substance means that it is less stable toward reaction
These principles are based on the contribution to the entropy that each kind of phase
makes to a system.
A gas at high pressure has less entropy (per mole) because it is less
free.
A liquid (or solute) at high concentration has less entropy because there are fewer
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- Spring '09
- KATZ
- Thermodynamics, Energy, Entropy
-
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