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Born-Haber Cycles

Born-Haber Cycles. The Born-Haber cycle is an enthalpy level diagram breaking down the formation of an ionic compound using simpler steps. The Born-Haber cycle can be used to find an unknown enthalpy value by applying Hess’s law Example: Calculate Δ H ꝋ latt for Na + (g) + Cl - (g).

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Born-Haber Cycles

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  1. Born-Haber Cycles • The Born-Haber cycle is an enthalpy level diagram breaking down the formation of an ionic compound using simpler steps. • The Born-Haber cycle can be used to find an unknown enthalpy value by applying Hess’s law Example: Calculate ΔHꝋlattfor Na+(g) + Cl-(g)

  2. Na+(g) + e- + Cl(g) Bond Dissociation(Cl2) 1stElectron Affinity (Cl) enthalpy Indirect route Na+(g) + Cl-(g) Na+(g) + e- + ½Cl2(g) 1st Ionisation(Na) Na(g) + ½Cl2(g) ∆Hlatt ∆Hat (Na) Direct Route Na(s) + ½Cl2(g) ∆Hf NaCl(s)

  3. Draw a Born-Haber cycle for magnesium oxide and use it to calculate the 2nd electron affinity of O

  4. Mg2+(g) + 2e- + O(g) Mg2+(g) + O2-(g) enthalpy Bond Dissociation(O2) 1stElectron Affinity (O) 2dn Electron Affinity (O) Mg2+(g) + 2e- + ½O2(g) Mg2+(g) + O-(g) 2nd ionisation (Mg) Mg+(g) + e-+ ½O2(g) 1st ionisation (Mg) ∆Hlatt Mg(g) + ½O2(g) ∆Hat (Mg) Mg(s) + ½O2(g) ∆Hf MgO(s)

  5. Using the values given in the table below, construct a Born-Haber cycle and calculate the ΔHꝋlatt for CaF2

  6. Ca2+(g) + 2e- + 2F(g) enthalpy Bond Dissociation 1stElectron Affinity Ca2+(g) + 2e- + F2(g) Ca2+(g) + 2F-(g) 2nd ionisation Ca+(g) + e- + F2(g) 1st ionisation Ca(g) + F2(g) ∆Hlatt ∆Hat Ca(s) + F2(g) ∆Hf CaF2(s)

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