Bohrn haber cycle of NaCl

Bohrn haber cycle of NaCl

1. Lattice energy and Born-Haber cycle Dr. Mithil Fal Desai Shree Mallikarjun and Shri Chetan Manju Desai College Canacona Goa

2. Lattice energy ( Δ H L or U) M + (g) + X - (g)  MX (s) + Δ H L Energy released when one mole of solid ionic compound is formed from its gaseous ions.

3. NaCl (s) Na + (g) + Cl - (g) Energy Na (s) + ½ Cl 2 (g) Na (g) + ½ Cl 2 (g) Na + (g) + e- (g) + Cl (g) Na + (g) + e- (g) + ½ Cl 2 (g) Δ H d = 120.9 kJ mol -1 Δ H f = 381.2 kJ mol -1 Δ H L = - 757.3 kJ mol -1 EA = - 348.6 kJ mol -1 I.E = 495.4 kJ mol -1 Δ H s = 108.4 kJ mol -1 NOT to scale

4. BOOKS

5. Born- Lande equation. U (1-1/n)   = Avogadro’s constant A = Madelung constant Z +,- = Charges on cation & anion = vacuum permittivity = fundamental charge = equilibrium interionic distance n = Born exponent  

6. Example

7. Examples

8. Consequences of lattice enthalpies Thermal stabilities of ionic solid Lattice energy of MgCO 3 more than BaCO 3 . MCO 3(s )  MO (s) +CO 2(g) Standard enthalpy of decomposition is given by ΔH decomposition = ΔH decomposition of carbonate + ΔH L {MCO 3 (s) } - ΔH L { MO (s) }   Lattice energy down the group decreases due to increase in interionic radius Formation of MgO is favoured over BaO as MgO has higher lattice energy than BaO . Change inter-ionic distance after decomposition is more significant for MgCO 3 Therefore decomposition will be favoured if ΔH L MO (s) more

9. Thermal stabilities of ionic solid MCO 3(s)  MO (s) + CO 2(g ) Standard enthalpy of decomposition is given by ΔH decomposition = ΔH decomposition of carbonate + ΔH L {MCO 3 (s) } - ΔH L { MO (s ) }     MCO 3(s) MO (s) + CO 2(g ) M 2+ (g) + (CO 3) 2- (g) M 2+ (g) + (CO 2 ) (g) +O 2- (g) ΔH decomposition ΔH dec of carbonate ΔH L MCO 3 (s ) ΔH L MO (s ) A B Relative change in lattice parameter is more in B case

10. Consequences of lattice enthalpies Thermal stabilities of ionic solid RSC Adv., 2012, 2, 6542-654 and Journal of Thermal Analysis and Calorimetry , 95(3 ). 999-1005.

11. Ionic radius and Lattice energy http://www.docbrown.info/page07/delta2Hb.htm

12. Stability of oxidation state

13. Why IF 7 and no IBr 7 Reaction is strongly spontaneous for X = F than other halogens Despite F has lower E. A. f ormation of formation of X - is more exothermic for F than Cl As cation increases the charge lattice energy increases however with increase in anion size this effect will decrease. As Iodine is having more radius this effect will be maximum for I.   Δ H L ∝  

14. S olubility http ://www.google.com/patents/WO2012109187A1?cl=en ΔH hyd ∝ { (1/r + ) + (1/r - ) } ΔH L ∝ {1/(r + + r - )}

15. Ohhhhh !!!!!!! Chemistry is….. 15