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HL5-9

Discussing the difference between theoretically and experimentally derived lattice energies 15.2.4. HL5-9.ppt. So far we’ve learned that although lattice enthalpy cannot be directly measured, it can be determined in two ways:. Theoretically using equations like this one

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HL5-9

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  1. Discussing the difference between theoretically and experimentally derived lattice energies 15.2.4 HL5-9.ppt

  2. So far we’ve learned that although lattice enthalpy cannot be directly measured, it can be determined in two ways: • Theoretically using equations like this one • ΔHlat˚=(Knm)/(RMn+ + RXm-) • Experimentally using Born Haber Cycles • Hlat = Hf – (Hatom(for both Na and Cl)+ Hi+ He) • Once again, the epic struggle between man’s mind and the universe that it lives in...

  3. Q – What does Empirical Mean? All values are for ΔHlat˚ in kJmol- % Diff = (Emp-Theo)/Emp

  4. A – Experimentally based! All values are for ΔHlat˚ in kJmol- % Diff = (Emp-Theo)/Emp

  5. Q – Does the Born-Haber Model agree with the ionic model? All values are for ΔHlat˚ in kJmol- % Diff = (Emp-Theo)/Emp

  6. A – Generally the agreement is good All values are for ΔHlat˚ in kJmol- % Diff = (Emp-Theo)/Emp

  7. Q – Deduce the relationship between the ionic/covalent nature of a bond and the agreement between the models. All values are for ΔHlat˚ in kJmol- % Diff = (Emp-Theo)/Emp

  8. A – The more ionic in nature a bond is, the more agreement there is. Compounds that are more covalent in nature have higher empirical values. All values are for ΔHlat˚ in kJmol- % Diff = (Emp-Theo)/Emp

  9. Summing up • Usually there is good agreement between empirical and theoretical values • If there isn’t good agreement: • It implies that the description of the compound as ionic is inappropriate • There could be a significant degree of covalent character in the bonding (EN difference less than 1.7) • Presence of covalent character leads to an increase in ΔHolat

  10. Homework • Get your A in gear and finish your IA soon. Or else… • A = Attitude • IA = Internal Assessment

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