Study Notes
Lattice energy and Born-Haber cycles are essential concepts in understanding the formation and stability of ionic compounds. Enthalpy change of atomization, ΔHat — the 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 — the enthalpy change when one mole of an ionic compound is formed from its gaseous ions. Example: Mg2+(g) + O2-(g) → MgO(s). First electron affinity, EA — the enthalpy change when one mole of gaseous atoms gains one electron to form gaseous ions with a single negative charge. Example: Cl(g) + e- → Cl-(g). Born-Haber cycle — a thermochemical cycle used to calculate lattice energy by considering various enthalpy changes. Example: Na(s) + 1/2 Cl2(g) → NaCl(s).
Exam Tips
Key Definitions to Remember
- Enthalpy change of atomization
- Lattice energy
- First electron affinity
- Born-Haber cycle
Common Confusions
- Confusing lattice energy with bond energy
- Misunderstanding the sign of electron affinity
Typical Exam Questions
- What is lattice energy? The enthalpy change when one mole of an ionic compound is formed from its gaseous ions.
- How do you construct a Born-Haber cycle? Identify the compound, write the balanced equation, break down steps, assign enthalpy changes, and apply Hess's law.
- Why do smaller ions have higher lattice energies? Smaller ions have stronger attractive forces due to shorter distances between ions.
What Examiners Usually Test
- Understanding of enthalpy changes in Born-Haber cycles
- Ability to calculate lattice energy using given data
- Explanation of trends in electron affinities