Lattice Enthalpy and Born-Haber Cycles · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Billing the Lattice

Science · Chemistry · ages 17-18
Name ______________________   Date ____________

  1. Which Born-Haber steps are endothermic and which are exothermic?

    • Atomisation and ionisation are positive while electron affinity and lattice formation are usually negative
    • All four steps are positive
    • All four steps are negative

  2. Put the Born-Haber steps in order.

    • Lattice formation, electron affinity, ionisation, atomisation
    • Atomisation, ionisation, electron affinity, lattice formation
    • Ionisation, lattice formation, atomisation, electron affinity

  3. How do ion size and charge affect lattice enthalpy?

    • Larger ions with smaller charges give the most exothermic values
    • Size and charge make no difference
    • Smaller ions with larger charges give the most exothermic values

  4. You know every Born-Haber step except lattice formation. How do you find it?

    • Measure it directly in a calorimeter
    • Subtract the known steps from the formation enthalpy
    • Copy the value from a perfect ionic model

  5. The steps must add to the formation enthalpy of -436. Atomisation gives 229, ionisation gives 496, electron affinity gives -349. What is the lattice enthalpy?

    Answer: ______________

  6. The cycle value disagrees with a perfect ionic model value. What does the gap suggest?

    • The calorimeter was miscalibrated
    • Some covalent character with shared electron density
    • The ions have zero charge

  7. The cycle value and the perfect ionic model agree closely, so strong covalent character is likely. This claim is true.

    Circle one:   True   False

  8. Magnesium forms 2+ ions while sodium forms 1+, and Mg2+ is smaller than Na+. Why is the lattice enthalpy of magnesium chloride so much larger?

    • Greater charge and smaller size pull the ions together harder
    • Magnesium has more electron shells than sodium
    • Chloride changes its charge in magnesium chloride
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Billing the Lattice W1-mt_pUku4iUjYa-s1

  1. Atomisation and ionisation are positive while electron affinity and lattice formation are usually negative · Breaking into atoms and removing electrons takes energy in, while gaining electrons and forming the lattice release it.
  2. Atomisation, ionisation, electron affinity, lattice formation · Make the gaseous atoms, ionise the metal, add electrons to the non metal, then form the lattice.
  3. Smaller ions with larger charges give the most exothermic values · Small highly charged ions attract each other hardest, so the lattice releases the most energy.
  4. Subtract the known steps from the formation enthalpy · The steps must sum to the formation enthalpy, so the missing one is the difference.
  5. -812 · -436 minus the known steps (229 + 496 - 349) gives -812.
  6. Some covalent character with shared electron density · A gap means the bonding is not purely ionic, so electrons are partly shared.
  7. False · Agreement supports a nearly ionic picture. A gap would be needed to claim sharing.
  8. Greater charge and smaller size pull the ions together harder · Higher charge plus smaller radius means far stronger attraction and a more exothermic lattice.
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