Review Vocabulary
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Solvent
Solute
Solution
Sublimation
Diatomic Molecules
Breaking bonds: energy
change
• Creating bonds: energy
change
• Periodic Trends for Ionic Size
for Metals and Non-metals
• Nonvolatile solute
• Intramolecular
bonding
– Covalent
– Ionic
– Metallic
• Intermolecular Forces
of attraction
– London Dispersion
(Van der Waals)
– Dipole-dipole
– H-bonding
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Enthalpy of Solution – the overall heat change
when a solute is dissolved in a solvent
 Dissolution of Ionic Solids:
•
Enthalpy of solution (ΔHsoln) depends on:
» Energies holding solute ions in crystal lattice.
» Attractive force holding solvent molecules together.
» Interactions between solute ions and solvent molecules.
• ΔHsoln = ΔHion-ion + ΔHdipole-dipole + ΔHion-dipole
• When solvent is water:
» ΔHsoln = ΔHion-ion + Δhhydration
»
Video: http://youtu.be/CLHP4r0E7hg
© 2012 by W. W. Norton & Company
Lattice Energy
 Lattice energy (U):
• The energy released when one mole of the ionic
compound forms from its free ions in the gas phase.
M+(g) + X−(g) → MX(s)
k
(
Q
Q
)
1
2
U=
d
• Where k is proportionality constant, depends on
lattice structure – usually the same for compounds
with the same or nearly the same structure.
© 2012 by W. W. Norton & Company
Comparing Lattice Energies
k
(
Q
Q
)
1
2
U=
d
Lattice energy depends on:
• ionic charge
• ionic radius
© 2012 by W. W. Norton & Company
ΔHion-ion
 Lattice energy (U)—energy released
when crystal lattice is formed.
 ΔHion-ion = energy required to remove
ions from crystal lattice.
ΔHion-ion = −U
And: ΔHsoln = ΔHhydration − U
(Example Problem 1)
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Melting Point and Lattice
Energy
 Ions that are tightly held together require
more energy to break apart
 How much energy depends upon the
nucleus-to-nucleus distance between ions
 As distance between ions increases, the
lattice energy decreases
 Also, k must be the same for all
compounds under consideration
© 2012 by W. W. Norton & Company
Melting Point and Lattic Energy
 Example: Rank the following in order of
increasing lattice energy (assume all have
the same solid structure and k value)
 NaF
 KF
 RbF
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Melting Point and Multivalent
Ionic Compounds
The columbic (electrostatic) attraction
between doubly charged spieces, or
between them and singly charged ions,
are much stronger than those between
singly charged ions and cations.
Example 2: Predict which compound has
the highest melting point: CaCl2, PbBr2 , or
TiO2. All have the same k and the radius
of Ti+4 is 60.5 p.m.
© 2012 by W. W. Norton & Company
Born-Haber Cycle
and Lattice Energy
 Born-Haber Cycle:
• Algebraic sum of enthalpy changes associated with formation
of ionic solid from constituent elements.
• E.g., Na(s) + ½ Cl2(g) → NaCl(s) ΔHf° = −411.2 kJ
 Steps:
1. sublimation of 1 mole Na(s) → Na(g)
= ΔHsub =
109 kJ
2. breaking bonds of ½ mole of Cl2(g)
= ½ ΔHBE
240kJ/n
3. ionization of 1 mole Na(g) atoms
= IE1
495 kJ
4. ionization of 1 mole Cl(g) atoms
= EA1
-349 kJ
5. formation of 1 mole NaCl(s) from ions(g) = U
© 2012 by W. W. Norton & Company
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Born-Haber Cycle for NaCl
ΔHf° = ΔHsub + ½ ΔHBE + IE1 + EA1 + U
© 2012 by W. W. Norton & Company
Born-Haber Cycle
 http://youtu.be/BbTZoJ_K_l4
 Video is embedded on the Chapter 11
Topic Page on
WCSUErmann.wikispaces.com website
© 2012 by W. W. Norton & Company
Calculating U
 ΔHf° = ΔHsub + ½ ΔHBE + IE1 + EA1 + U
 Rearrange to solve for U
 U = ΔHf° - ΔHsub - ½ ΔHBE - IE1 - EA1
© 2012 by W. W. Norton & Company
Born-Haber Cycle: ΔHhydration
 The Born-Haber Cycle can also be used to
determine the Enthalpy of Hydration.
 Once we have found U, we can find
Δhhydration.
© 2012 by W. W. Norton & Company
Born-Haber Cycle: ΔHhydration
 ΔHsolution,NaCl = ΔHhydration,NaCl(aq) – UNaCl
 ΔHhydration,NaCl(aq) = ΔHhydration,Na+(g) + ΔHhydration,Cl−(g)
© 2012 by W. W. Norton & Company
Enthalpies of Hydration
© 2012 by W. W. Norton & Company
Vapor Pressure
 Vapor pressure:
• Pressure exerted by a gas in equilibrium
with its liquid.
• Rates of evaporation
and condensation are
equal.
© 2012 by W. W. Norton & Company