Lattice Energy

Question 1

Define: lattice energy

Answer 1

The enthalpy change when one mole of an ionic solid is formed from its isolated gaseous ions

Question 2

Explain the effect of ionic charge and ionic radius on the magnitude of lattice energy

Answer 2

Greater ionic charge and smaller ionic radius means higher charge density. Higher charge density means the ion attracts the other ion more strongly so lattice energy is more exothermic (greater magnitude)

Question 3

Define: 1st electron affinity

Answer 3

The enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to form one mole of gaseous -1 ions under standard conditions

Question 4

Explain why the second electron affinity is endothermic

Answer 4

Energy is needed to overcome the repulsion between the electron and anion

Question 5

Define: enthalpy change of solution

Answer 5

The energy change when one mole of an ionic solid dissolves in excess water to form an infinitely dilute solution.

Exothermic: soluble; endothermic: insoluble

SOLution for SOLid

Question 6

Define: enthalpy of hydration

Answer 6

The energy change when one mole of gaseous ions dissolves in excess water to form an infinitely dilute solution

Always exothermic as ions form ion-dipole bonds with H2O

Question 7

Describe and explain the trend in solubility of Group 2 hydroxides down the group

Answer 7

Solubilities increase down the group (HYdroxides go HIgher)

Cation charge density decreases so ions separate more easily

Question 8

Describe and explain the trend in solubility of Group 2 sulfates down the group

Answer 8

Solubility decreases

H(hyd) of cation decreases due to decreases charge density

H(latt) of sulfate decreases but to a lesser extent as sulfate ion, which is larger and so contributes more to H(latt), remains unchanged.

H(sol) = H(hyd) - H(latt) becomes more negative down the group so less soluble