5.2.1 Lattice Enthalpy

Question 1

Lattice enthalpy definition

Answer 1

Enthalpy change that accompanies formation of one mole of an ionic compound from its gaseous ions under standard conditions
Measure of the strength of ionic bonding in a giant ionic lattice

Question 2

Value of lattice enthalpy

Answer 2

Always exothermic, negative change

Question 3

Born-Haber cycle equation

Answer 3

Enthalpy change of formation (negative) = enthalpy change of atomisation + ionisation energy + electron affinity (negative) + lattice enthalpy (negative)

Question 4

Definition of standard enthalpy change of solution

Answer 4

Enthalpy change that takes place when one mole of a solute dissolves in a solvent
(Endothermic or exothermic)

Question 5

Definition of enthalpy change of hydration

Answer 5

Enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions
Always exothermic

Question 7

Equation linking lattice enthalpy, enthalpy change of hydration and solution

Answer 7

Enthalpy change of hydration = lattice enthalpy + enthalpy of solution

Question 8

How does ionic size affect lattice enthalpy

Answer 8

Increasing ionic radius:
- attraction between ions decreases
- lattice enthalpy is less negative
- melting point decreases

Question 9

How does ionic charge affect lattice enthalpy

Answer 9

Increased ionic charge:
- attraction between ions increases
- lattice enthalpy more negative
- melting point increases

Question 10

What does melting point indicate about lattice enthalpy

Answer 10

High melting point= very exothermic lattice enthalpy
But also dependent on packing of ions in an ionic lattice

Question 11

How does ionic size affect enthalpy of hydration

Answer 11

Increasing ionic radius:
- attraction between ions and water decreases
- hydration energy less negative

Question 12

How does ionic charge affect hydration enthalpy

Answer 12

Increasing ionic charge:
- attraction with water molecules increases
- hydration enthalpy more negative

Question 13

How can solubility of an ionic compound be predicted with hydration enthalpy

Answer 13

Lattice enthalpy needed to be overcome to dissolve ionic compound
So:
Sum of hydration enthalpies larger than lattice enthalpy: compound should dissolve
But also depends on temperature and entropy