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 (ΔH soln ) depends on: »Energies holding solute ions in crystal lattice. »Attractive force holding solvent molecules together. »Interactions between solute ions and solvent molecules. ΔH soln = ΔH ion-ion + ΔH dipole-dipole + ΔH ion-dipole When solvent is water: » ΔH soln = ΔH ion-ion + Δh hydration » Video:

© 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) 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 Lattice energy depends on: ionic charge ionic radius

© 2012 by W. W. Norton & Company ΔH ion-ion  Lattice energy (U)—energy released when crystal lattice is formed.  ΔH ion-ion = energy required to remove ions from crystal lattice. ΔH ion-ion = −U And: ΔH soln = ΔH hydration − 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 © 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 © 2012 by W. W. Norton & Company

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: CaCl 2, PbBr 2, or TiO 2. 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 Cl 2 (g) → NaCl(s) ΔH f ° = −411.2 kJ  Steps: 1. sublimation of 1 mole Na(s) → Na(g) = ΔH sub = 109 kJ 2. breaking bonds of ½ mole of Cl 2 (g) = ½ ΔH BE 240kJ/n 3. ionization of 1 mole Na(g) atoms = IE kJ 4. ionization of 1 mole Cl(g) atoms = EA kJ 5. formation of 1 mole NaCl(s) from ions(g) = U?

© 2012 by W. W. Norton & Company Born-Haber Cycle for NaCl ΔH f ° = ΔH sub + ½ ΔH BE + IE 1 + EA 1 + U

Born-Haber Cycle   Video is embedded on the Chapter 11 Topic Page on WCSUErmann.wikispaces.com website © 2012 by W. W. Norton & Company

Calculating U  ΔH f ° = ΔH sub + ½ ΔH BE + IE 1 + EA 1 + U  Rearrange to solve for U  U = ΔH f ° - ΔH sub - ½ ΔH BE - IE 1 - EA 1 © 2012 by W. W. Norton & Company

Born-Haber Cycle: ΔH hydration  The Born-Haber Cycle can also be used to determine the Enthalpy of Hydration.  Once we have found U, we can find Δh hydration. © 2012 by W. W. Norton & Company

Born-Haber Cycle: ΔH hydration  ΔH solution,NaCl = ΔH hydration,NaCl(aq) – U NaCl  ΔH hydration,NaCl(aq) = ΔH hydration, Na + (g) + ΔH hydration,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.