Born–Haber cycle: NaCl template

Enthalpy-level Born–Haber cycle for sodium chloride: sublimation +107, ½ bond enthalpy +122, ionisation +496, electron affinity −349, lattice −787 and ΔfH° −411 kJ mol⁻¹, with the sum shown.

What the template shows

• Hess's law around the formation of an ionic solid from its elements (kJ mol⁻¹, energy to scale)
• ½ Bond enthalpy of Cl₂
• First ionisation energy of Na
• Electron affinity of Cl
• Lattice enthalpy
• Going round the cycle, the enthalpy changes add up to ΔfH°(NaCl): the route through gaseous ions equals the direct one.
• The lattice enthalpy cannot be measured directly; it is the term that closes the cycle.
• Forming the lattice (−787) more than pays for making the ions (+496 − 349): that is why NaCl is stable even though Na⁺ + Cl⁻ in the gas are higher than the atoms.
• Sign convention: lattice enthalpy here is for forming the solid from gaseous ions (exothermic); for breaking it up it is +787 kJ mol⁻¹.
• Every part of this figure is editable · sources on the template card

Drawn with 26 shapes – every one editable in MolDraw.

Sources

• Housecroft & Sharpe, Inorganic Chemistry, 5th ed., Pearson 2018, ch. 6 Textbook
• Atkins, de Paula & Keeler, Atkins' Physical Chemistry, 11th ed., OUP 2018, ch. 2 Textbook
• NIST Chemistry WebBook: sodium chloride Database