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Lattice Energy, D U lattice

Lattice Energy, D U lattice. The change when one mole of a solid crystal formed from its ions, atoms, molecules in their gaseous state ,its always negative Relates to the endothermic process MX(s)  M + (g) + X - (g)

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Lattice Energy, D U lattice

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  1. Lattice Energy, DUlattice • The change when one mole of a solid crystal formed from its ions, atoms, molecules in their gaseous state ,its always negative Relates to the endothermic process MX(s) M+(g) + X-(g) • NaCl(s) Na+(g) + Cl-(g) DHlattice= 769 kJ/mol Endothermic reactions

  2. Factors affecting the lattice enthalpy • 1-The greater the charge of the ions, the stronger the electrostatic attraction

  3. Factors affecting the lattice enthalpy 2-smaller the ionic radius, shorter the distance, stronger the electrostatic attraction

  4. Example 1 N3– O2– F– increasing lattice formation enthalpy K+ Na+ Li+ • high charge • small size.

  5. Example 2 Ion DHhyd (kJmol–1) Ion DHhyd (kJmol–1) Ion DHhyd (kJmol–1) Ion DHhyd (kJmol–1) • The size of the ion. The smaller the ion, the larger the enthalpy of hydration. Li+ –519 F– –506 increasing size Na+ –406 Cl– –364 K+ –322 Br– –335 • The charge on the ion. The larger the charge on the ion, the larger the enthalpy of hydration. Fe2+ –1950 Fe3+ –4430

  6. Lattice energy: estimates from an electrostatic model Born landel equation N= Avogadros constant =6.022 *10 M= Madlonuge constant

  7. The lattice energy is estimated in joules per mole of compound

  8. n = Born exponent

  9. Lattice energy: the Born-Haber cycle • To determine the lattice enthalpy and the degree of ionic character of a salt (Hess’ law) • .

  10. Worked example :the Born-Haber cycle Given that the standard enthalpy of formation at 298 K of CaF2 is -1228 kJ mol-1, determine the lattice energy for CaF2 using appropriate data from the Appendices.

  11. 1-standard enthalpy of formation is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements, in their standard states.(usually 1atm , 298.15 K). 2-standard enthalpy of sublimation (atomization), is the heat required to change 1mole of a substance from solid state to gaseous state at usually standard temperature and pressure (STP) 3-standard dissociation energyis the change of enthalpy  to break 1mole of a bond to give separate atoms

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