Summary
Lattice energy is the enthalpy change when one mole of an ionic compound forms from its gaseous ions. It indicates the strength of ionic bonds in a solid lattice. Enthalpy change of atomization — energy change when one mole of gaseous atoms is formed from its element in its standard state. Example: K(s) → K(g). Lattice energy, ΔHlatt — energy change when one mole of an ionic compound is formed from its gaseous ions. Example: Mg2+(g) + O2-(g) → MgO(s). Electron affinity — enthalpy change when one mole of gaseous atoms gains an electron to form negative ions. Example: Cl(g) + e- → Cl-(g). Born-Haber cycle — a thermochemical cycle used to calculate lattice energy. Example: Na(s) + 1/2 Cl₂(g) → NaCl(s).
Exam Tips
Key Definitions to Remember
- Enthalpy change of atomization
- Lattice energy
- Electron affinity
Common Confusions
- Confusing lattice energy with enthalpy change of atomization
- Misunderstanding the sign of electron affinity (exothermic vs endothermic)
Typical Exam Questions
- What is lattice energy? Energy change when an ionic compound forms from gaseous ions.
- How do you calculate lattice energy using a Born-Haber cycle? Use Hess's law to sum enthalpy changes.
- What factors affect lattice energy? Ionic charge and ionic radius.
What Examiners Usually Test
- Understanding of Born-Haber cycles
- Ability to calculate lattice energy
- Knowledge of factors affecting lattice energy