22.3 - Factors affecting lattice enthalpy and hydration

Question 1

What are the two factors that affect lattice enthalpy?

Answer 1

1. Ionic radius
2. Ionic charge

Question 2

Describe the effect of ionic radius on lattice enthalpy (+ melting point)

Answer 2

• Ionic radius increases down the group
• The attraction between ions decreases as the charge on the ions are more spread out when ionic radii are larger, since the distance between the ion centres increases
• So the lattice energy is less negative/exothermic
• Therefore the melting point decreases

Question 3

Describe the effect of ionic charge on lattice enthalpy (+ melting point)

Answer 3

• Ionic charge increases across rows
• The attraction between ions increases as the greater the ionic charge, the higher the charge density
• So lattice energy becomes more negative/exothermic
• Therefore the melting point increases

Question 4

What are the two factors that affect hydration enthalpy?

Answer 4

1. Ionic radius
2. Ionic charge

Question 5

Describe the effect of ionic radius on hydration enthalpy

Answer 5

• Ionic radius increases down the group
• The attraction between ions and water molecules decreases as the charge on the ions are more spread out when ionic radii are larger, since the distance between the ion centres increases
• So the hydration energy is less negative/exothermic

Question 6

Describe the effect of ionic charge on hydration enthalpy

Answer 6

• Ionic charge increases across rows
• The attraction between ions and water molecules increases as the greater the ionic charge, the higher the charge density
• So hydration energy becomes more negative/exothermic