OCR Advanced GCE in Chemistry/Lattice enthalpy/Answers

Answers
1. Na+ has larger radius than Mg2+

Br- has larger radius than cl-

Na+ has lower charge than Mg2+

Therefore Stronger attraction between MgCl2 ions

2. rearrange:

enthalpy change of formation = atomisation enthalpies + electron affinity + lattice enthalpy

3. The size of the ions The charge of the ions

4. The first electron affinity is the enthalpy change when one electron is added to each gaseous atom in one mole, to form one mole of 1- ions

5. Increasing temperature down group, this is because down the group, ionic radius increase, so charge density decrease, so thermal stability increases down the group.

Distorted ion breaks down more easily