review vocabulary solvent solute solution sublimation diatomic molecules breaking bonds: energy...

Review Vocabulary

• 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

© 2012 by W. W. Norton & Company


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

http://youtu.be/CLHP4r0E7hg


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)

– Where k is proportionality constant, depends on lattice structure – usually the same for compounds with the same or nearly the same structure.

dQQkU )( = 21


Comparing Lattice Energies

Lattice energy depends on:• ionic charge• ionic radius

dQQkU )( = 21


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)

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


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


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.



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 ?


Born-Haber Cycle for NaCl

ΔHf° = ΔHsub + ½ ΔHBE + IE1 + EA1 + U

Born-Haber Cycle

http://youtu.be/BbTZoJ_K_l4 Video is embedded on the Chapter 11

Topic Page on WCSUErmann.wikispaces.com website


http://youtu.be/BbTZoJ_K_l4

Calculating U

ΔHf° = ΔHsub + ½ ΔHBE + IE1 + EA1 + U

Rearrange to solve for U U = ΔHf

° - ΔHsub - ½ ΔHBE

- IE1 - EA1


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.



Born-Haber Cycle: ΔHhydration

ΔHsolution,NaCl = ΔHhydration,NaCl(aq) – UNaCl

ΔHhydration,NaCl(aq) = ΔHhydration,Na+(g) + ΔHhydration,Cl−(g)


Enthalpies of Hydration


Vapor Pressure

Vapor pressure:• Pressure exerted by a gas in equilibrium

with its liquid.• Rates of evaporation

and condensation are equal.

review vocabulary solvent solute solution sublimation diatomic molecules breaking bonds: energy...

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