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IB Chemistry HL 1.2.5 Hl Born Haber Cycle Questions

Use real HL exam cycles to identify energy steps, calculate lattice enthalpy and justify ionic-charge and radius comparisons.

Syllabus
First assessment 2025
Course
Chemistry HL
Level
HL

Exam points

  • Construct or interpret a Born–Haber cycle by naming species and energy steps, including atomization, ionization, electron affinity and lattice enthalpy with correct signs.
  • Calculate a lattice enthalpy or formation enthalpy from the signed sum of the other Born–Haber steps, showing the Hess-cycle equation and units.
  • Explain or compare lattice-enthalpy magnitude using ionic charge and ionic radius, relating smaller ions or higher charges to stronger electrostatic attraction.

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Study 1.2.5 (HL)—Born-Haber cycle conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Chemistry HL 1.2.5 Hl Born Haber Cycle Questions question 1

[Maximum number: 6]

Magnesium, a reactive metal found in many common minerals, is also an essential nutrient for both plants and animals.

Question (a)

(a)

Although magnesium is usually found as Mg2+\mathrm{Mg}^{2+} in its compounds, it is possible to use the Born-Haber cycle to investigate the possibility of Mg+\mathrm{Mg}^{+}being able to form stable compounds.

Use the ionization energy data from part (b), along with the other data provided below, to determine the enthalpy change of formation of MgCl(s). Assume that, because Mg+\mathrm{Mg}^{+} would be similar in size to Na+,MgCl\mathrm{Na}^{+}, \mathrm{MgCl} would have a similar lattice enthalpy to NaCl .

 Enthalpy of atomization of Mg +146 kJ mol−1 Bond enthalpy in Cl2+243 kJ mol−1 Electron affinity of Cl−349 kJ mol−1 Lattice enthalpy of NaCl+790 kJ mol−1\begin{array}{ll} \text { Enthalpy of atomization of Mg } & +146 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ \text { Bond enthalpy in } \mathrm{Cl}_{2} & +243 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ \text { Electron affinity of } \mathrm{Cl} & -349 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ \text { Lattice enthalpy of } \mathrm{NaCl} & +790 \mathrm{~kJ} \mathrm{~mol}^{-1} \end{array}
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Question (b)

(b)

Consider the lattice enthalpies of MgF2,MgCl2\mathrm{MgF}_{2}, \mathrm{MgCl}_{2} and CaCl2\mathrm{CaCl}_{2}. List these from the most endothermic to the least endothermic and explain your order.
Most endothermic
Least endothermic

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