Lattice energy

Question 1

Predict and explain the variation in enthalpy change of hydration for the ions F-,Cl-,Br- and I- (2)

Answer 1

Becomes less exothermic down the group from F to I and due to increase in size, there is a decrease attraction to water or weak ion-dipole force to water.

Question 2

Define lattice energy (2)

Answer 2

Energy change when one mole of an ionic compound is formed from its gaseous ions.

Question 3

The solubility of group 2 hydroxides increases down the group. Explain this trend. (3)

Answer 3

ΔLatt and ΔHyd become less exothermic/less negative .
ΔHyd changes less by a smaller extent and Δlatt changes faster
ΔSol becomes exothermic/more negative

Question 4

FeCO3 decomposes at a lower temperature than NiCO3. Suggest a possible reason for this difference (2)

Answer 4

Fe 2+ has a smaller radius and has a greater charge density. It polarises CO3^2- more.