Born-Haber Cycles Flashcards
Explain a born haber cycle
Metal element and none metal element with endo arrow to gaseous ions by atomising and ionising, then from gaseous ions to compound by lattice energy and from the elements to compound by enthalpy change of formation of compound
Why are born haber cycles used
As all the energy changes in the cycle can be determined from experimental data except the lattice energy
How to calculate lattice energy from born-Haber cycle
Enthalpy of formation - (enthalpy of atomisation and ionisation of elements)
Are ionisation and atomisation energies exo or endo
Endo
Which are the exothermic processes of born-haber cycle
Lattice energy, standard enthalpy change of formation, first electron affinity
Born haber cycle for Na2O
2Na(s) + 1/2 O2(g)
Atomisation x2 Na 2Na(g) + 1/2 O2
2IonisationNa 2Na+(g) + 2e- + 1/2 O2(g)
Atomisation O 2Na+ + 2e- + O(g)
Sum of first and second EA for O
2Na+(g) + O2-(g)
Lattice energy of sodium oxide
Na2O(s)
Also from the atoms to Na2O(s) for standard enthalpy change of formation
What does the perfect ionic model assume
All ions are perfectly spherical
Charge is distributed evenly throughout the ion
The ions display no covalent character
What is polarisation
Electron cloud distortion of ions
Which anions most easily polarised
Large electron cloud and high charge, electrons less strongly attracted to nucleus
Which cations most easily polarise
Small ionic radius high charge, draw electron density towards them from anion
Which is less exo theoretical or born-Haber calculated value and why
Theoretical less exo as ignores any covalency so less energy released when just ionic bonds form rather than born-haber where some polarisation so covalent and ionic bonds formed and more energy released
Is fluorine polarisable and why
No or very little as electrons strongly attracted to nucleus and little shielding
