Solutions and Chemical Equilibrium

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Solutions and Chemical Equilibrium
Preparation for College Chemistry Columbia
University Department of Chemistry
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Chapter Outline
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Types of Solutions
Phase
Solute
Solvent
Example
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Concentration of Solutions
Definition
Units
Symbol
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Mass Solute
When concentration is so low that the d dwater
ppm solute(aqueous solutions) mg solute /
Lsolution
ppb solute mass x 10 9
ppb solute (aqueous solutions) µg solute /
Lsolution
http//pubs.acs.org80/hotartcl/est/99/oct/oct-new
s5.html
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Molarity

M
solute
What volume of a 0.035 M AgNO3 solution can be
made from 5.0 g AgNO3 ?
5.0 g AgNO3
x
840 mL
x

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Dilution Equation
Only solvent is added
Preparing a dilute solution of specified
concentration
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Raoults Law
P1
Basis for four properties of DILUTE SOLUTIONS
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Colligative Properties
Depend on the concentration of solute species and
not on its nature

• Freezing point depression. Kf (C kgsolvent
  mol -1solute)

• Boiling point elevation Kb (C kgsolvent mol
  -1solute)

• Vapor-pressure lowering (atm)

• Osmotic Pressure (atm)

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Vapor-pressure of liquids
Pressure exerted by a vapor in equilibrium with
its liquid
For water
Atmospheric pressure
boiling point
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Vapor-pressure lowering
For a two component system solvent 1, solute
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Raoult Law
The vapor pressure lowering is
The change in vapor pressure of the solvent is
proportional to the mole fraction of the solute
(lt 0)
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Boiling Point Elevation (?Tb) Vapor Pressure
lowering (?P1)
1 atm
Solvent vapor pressure
Temperature
Tb
Tb
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?Tb and ?Tf
?Tb Tb - Tb Kbm
?Tf Tf - Tf -Kfm
?Tb b.p. elevation
Kb b.p. elevation constant
?Tf f.p. depression
Kf f.p. depression constant
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Kf and Kb (C kgsolvent mol -1solute)
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Osmosis and Osmotic Pressure, p
Jacobus vant Hoff in 1887
c M R universal gas constant T absolute
temperature
Solution
Pure water
Semipermeable membrane
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Chemical Equilibrium
N2O4
2NO2
2NO2
N2O4
N2O4
2NO2
REVERSIBLE REACTION
forward
PRODUCTS
REACTANTS
reverse
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Kinetics. Rates of Reaction
RATEforward RATEreverse
Reaction rate
Equilibrium
Time
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Chemical Equilibrium
Saturated solution
Weak electrolyte dissociation
Complex ion formation
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LeChateliers Principle
A system in equilibrium that is subjected to a
stress will react in ways that counteract the
stress
Four ways to stress a chemical system

• Concentration Change

• Volume Change

• Temperature Change

• Presence of a Catalyst

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Equilibrium Constants, Keq
Kc
Kp
LAW OF MASS ACTION. Guldberg and Waage. 1867
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Reaction Quotient, Q
Reaction quotient
Q K
Time
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Writing Equilibrium Constants

• Gases enter equilibrium expressions as
  partial
• pressures in atm

• Dissolved species enter as concentrations in
  M

• Pure solids and pure liquids are represented
  by the
• number 1 (unity)

• A solvent in a chemical reaction is
  represented by 1,
• provided the solution is diluted

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Ion Product Constant for Water, KW
Autoionization of Water

55.5 M
H2O