Reaction Equilibrium in Nonideal Systems

1
Chapter 11
Nonideal Systems
Physical Chemistry

• Reaction Equilibrium in Nonideal Systems

2
The Equilibrium Constant
Nonideal Systems
Physical Chemistry
For the ideal-gas reaction
the equilibrium condition
3
The Equilibrium Constant
Nonideal Systems
Physical Chemistry
(11.4)
(11.5)
(11.6)
Standard equilibrium constant
Activity equilibrium constant
Equilibrium constant
4
Reaction Equilibrium in nonelectrolyte solutions
Nonideal Systems
Physical Chemistry
5
Reaction Equilibrium in nonelectrolyte solutions
Nonideal Systems
Physical Chemistry
6
Reaction Equilibrium in electrolyte solutions
Nonideal Systems
Physical Chemistry
Many ionic reactions in solution are acid-base
reactions.
Brønsted definition of acid/base
Acid a proton donor Base a proton acceptor
water amphoteric, either a proton donor or a
proton acceptor
The standard state of the solvent H2O is pure H2O.
7
Reaction Equilibrium in electrolyte solutions
Nonideal Systems
Physical Chemistry
In aqueous solutions
For dilute aqueous solutions
Omission of the solvents activity.
For the H2O ionization
8
Reaction Equilibrium in electrolyte solutions
Nonideal Systems
Physical Chemistry
For the ionization of the weak acid HX in aqueous
solution
In dilute solution
The pair of ions H3O/X-
9
Reaction Equilibrium in electrolyte solutions
Nonideal Systems
Physical Chemistry
For an aqueous solution of the weak acid HX with
stoichiometric molality m, the degree of
dissociation ?
Ka has a dimension of m
10
Reaction Equilibrium involving pure solids or
pure liquids
Nonideal Systems
Physical Chemistry
Many reactions involve one or more pure solids or
liquids.
equilibrium condition
at const. T
11
Reaction Equilibrium involving pure solids or
pure liquids
Nonideal Systems
Physical Chemistry
at const. T
Since solids and liquids are rather
incompressible Vm,i is independent of P
12
Reaction Equilibrium involving pure solids or
pure liquids
Nonideal Systems
Physical Chemistry
Consider the equilibrium
If P is not very high
Must include solids!
13
Reaction Equilibrium involving pure solids or
pure liquids
Nonideal Systems
Physical Chemistry
Consider the equilibrium between a solid salt
Solubility product (SP) equilibrium constant
Valid for any salt (only slightly soluble in
water)!
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Using the limiting law to analyze an equilibrium
Nonideal Systems
Physical Chemistry
Answer.
(a) The equilibrium constant for the dissolution
of AgCl is
The ionic strength of the solution is (11
electrolyte)
15
Using the limiting law to analyze an equilibrium
Nonideal Systems
Physical Chemistry
Answer.
(a) The equilibrium constant for the dissolution
of AgCl is
The ionic strength of the solution is (11
electrolyte)
16
Using the limiting law to analyze an equilibrium
Nonideal Systems
Physical Chemistry
Answer.
(b) The ionic strength of the solution is (12
electrolyte)
The solubility of potassium sulfate in water is
1.7?10-5 mol/kg.
17
Physical Chemistry
Nonideal Solutions
Homework
P337, Section 11.1
11.1
P337, Section 11.3
11.5, 11.6, 11.9, 11.14
P338-339, Section 11.4
11.27, 11.30, 11.31, 11.32
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Reaction Equilibrium in nonideal gas mixtures
Nonideal Systems
Physical Chemistry
The activity ai of component i of a nonideal gas
mixture is
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The Equilibrium Constant(T dependence)
Nonideal Systems
Physical Chemistry
20
The Equilibrium Constant (P dependence)
Nonideal Systems
Physical Chemistry
21
Summary of Standard States
Nonideal Systems
Physical Chemistry
Table 11.1
Substance Standard state
Gas (pure or in gas mixture)
Pure ideal gas at 1 bar and T
Pure liquid or pure solid
Pure substance at 1 bar and T
Solution component, I
Pure i at T and P of solution
Pure A at T and P of solution
Solvent A
Nonelectrolyte solute II
Fictitious state xi1?II,i
Electrolyte solute m-scale
Fictitious state ? ?1 ? ? m,i /mo
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Gibbs Energy Change for a Reaction
Nonideal Systems
Physical Chemistry
Biochemists use
23
Physical Chemistry
Nonideal Solutions
Homework
P339, Section 11.5
11.33, 11.35
P339, Section 11.6
11.36
P339, Section 11.7, 11.9
11.37, 11.38, 11.41, 11.44
P339-340, General
11.46, 11.47